WASH & EPIDEMIOLOGY

INDIAN INSTITUTE OF PUBLIC HEALTH GANDHINAGAR
(A University formed under IIPHG Act, 2015 of Government
of Gujarat)
Certificate course in Community Health (CCCH)
Module-1
Front

Module – I course outline
2/18/2020 2Mrs. Arpita Vaidya

UNIT 3: Environment including Water,
Sanitation And Hygiene (WASH)
• Course overview
• The overall aim of the course is to provide the
students with a scientific understanding of the
concepts related to environment and WASH;
possible approaches to assess, communicate
and control major environmental hazards.

Learning Objectives
• Upon completion of this course, participants will
be able to:
1. Understand basic concepts in environmental
health
2. Understand basic concepts in WASH,
3. Water different sources, parameters of water
quality and Water Disinfection
4. Understand the basic concepts of Sanitation
5. Solid Waste and its management

Essential Readings:
• 1. Dade W Moeller. Environmental health. Harvard University
Press, 2004
• 2. Maxcy- Rosenau-Last. Public health and preventive medicine,
15 edition, 2007.
• 3. Park K. Park’s Text book of Preventive and Social Medicine.
Banarsi Das Bhanot and Sons Publishers, Jabalpur, 23rd Ed.
• 4. Central Industrial Hygiene Association, India. Indian journal of
occupational hygiene and safety (quarterly publication)
• 5. WHO (1972). Health hazards of the human environment,
WHO, Geneva
• 6. Govt of India, ICMR (1975). Manual of standards for Drinking
water. ICMR Report No.44, 1975.

Environment
• Environment is usually defined as the external
factor/factors present around humans and
does have an influence on the health of the
human. Environment that has an impact on
human health can be divided into four
components:
• 1. Physical environment
• 2. Biological environment
• 3. Social environment
• 4. Cultural environment

Components of Environment
1. Physical
environment
• This consists of non-
living things and
certain physical
forces/ energy present
around man. These are
water, air, soil, housing,
radiation, light, noise,
dirt, wastes, etc.
2/18/2020 Mrs. Arpita Vaidya 7

2. Biological
environment
• This consists of living
things around man.
These are plants,
animals, rodents,
insects and microbes
like bacteriae, viruses,
rickettsiae, parasites,
fungi, etc.

• Social environment
• This consists of
occupation, literacy,
income, religion,
standard of living,
lifestyle, availability of
health services, etc.

• Cultural environment
• This consists of
knowledge, attitude,
beliefs practices,
traditions, culture,
customs, habits, etc.
Cultural environment of
man is affected by other
factors such as
urbanization, migration,
mechanization etc.

WASH
• Water, sanitation and hygiene (WASH) are
fundamental to health. Despite progress on
child mortality(Death(Morbidity - illness)),
infectious diseases still pose the largest
threat to the health of young children.

WATER

WATER
• Water has got an influence on the health/life of an individually.
• It is related directly because water is essential for digestion,
regulation of body temperature, removal of the wastes from
the body through tears, perspiration, urine and feces and for
lubricating the joints.
• It also acts as a buffer by neutralizing the acids produced in
the body. Moreover, it is a necessary fuel /vehicle for all
metabolic processes in the body.
• Deficiency of water in the body causes dehydration, acidosis,
shock, urinary tract infections, indigestion and constipation.
• Water has an influence on the health of the human beings
indirectly also. It acts as a vehicle for transmission of many
communicable diseases like typhoid, diarrheal diseases, viral
hepatitis A, etc.

WATER
• Water also constitutes the breeding place for
the mosquitoes, which transmit many diseases
to human beings, like malaria, filariasis,
Japanese encephalitis, dengue fever, etc.
• Man also needs water for domestic purposes
such as cooking, washing clothes, cleaning
utensils, gardening and above all for drinking.
• He also needs it for commercial, industrial and
recreational purposes.

WATER
• Safe drinking water, sanitation, and hygiene are the three
most important conditions for keeping communities healthy.
•
• They contribute to the prevention and control of disease, injury,
and disability.
• Thus to reduce the global impact of disease, we need to
understand how certain underlying causes lead to disease.
• Many such underlying causes are often closely linked to water,
sanitation, and hygiene conditions.

WATER
• The establishment of SDG 6 (Sustainable
Development Goal), Ensure availability and
sustainable management of water and sanitation for
all, reflects the increased attention on water and
sanitation issues in the global political agenda.
• The 2030 Agenda lists rising inequalities, natural
resource depletion, environmental degradation and
climate change among the greatest challenges of our
time.
• It recognizes that social development and economic
prosperity depend on the sustainable management
of freshwater resources and ecosystems and it
highlights the integrated nature of SDGs.

WATER
• Adequate water, sanitation and hygiene are essential
components of providing basic health services. The
provision of WASH in health care facilities also
serves to prevent infections and spread of disease,
protect staff and patients, and uphold the dignity of
vulnerable populations including pregnant women
and the disabled.
• Many health care facilities in low resource settings
have no WASH services, severely compromising the
ability to provide safe and people-centered care and
presenting serious health risks to both health care
providers and those seeking treatment.

• Fecal–oral diseases can proliferate rapidly,
sometimes to epidemic proportions, when
people in crowded conditions lack clean
water for hygiene and sanitation.
• Among the agents involved are at least 20
viral, bacterial, and protozoan pathogens
that cause diseases such as cholera,
bacillary dysentery, and the relatively
recently discovered hepatitis E.

• Aid groups are combating these pathogens
with WASH, an integrated approach to disease
prevention that ensures not only that people in
emergency situations have water and
sanitation infrastructure, but also that they
practice behaviors that prevent disease.
• Diarrhea which is one of the life threatening
Public Health Problem may not seem deadly to
those who are residing in developed localities
who have access to improved sanitation.

• Nevertheless, it kills three-quarters of a million children
every year, more than malaria, AIDS, and measles
combined. But access to water isn’t enough; health-
protective behaviors are critically important. Worldwide,
only 19% of people on average are estimated to wash their
hands with soap after defecating.
• Although workers can install latrines and teach the value of
hand washing and latrine use, only the refugees themselves
can choose to change their behaviors. And that means
changing social norms. Open defecation is common
practice in developing nations. Hand washing is often done
without soap, and cultural traditions such as eating with
the hands and sharing plates can spread infectious
diseases.

The ‘F diagram,’” fecal–oral disease
transmission pathways (see figure).

Major Sources of Water
• There are various different sources of water
• 1. Rivers and streams:
• 2. Lakes:
• 3. The sea:
• 4. Rainwater:
• 5. Wells:
• 6. Reservoirs

• 1. Rivers and streams: Rivers and streams are a source of
fresh (i.e. not salty) water. River water is generally safest
to drink close to the source – the spring. However, it is also
true that river water can absorb minerals if it flows a
certain way through mineral rich rock and so to get the
benefit of these minerals it can be a good idea to let your
river water flow awhile through mineral deposits to get
the full benefit of it. The source of the river is called the
head, and the end of the river – the point at which it flows
into the sea – is known as the mouth.
• 2. Lakes: Lakes are still bodies of (usually fresh) water.
They are replenished by the rain and often by rivers and
streams, too. Some lakes are natural lakes, forming in
valleys in hilly or mountainous regions. Others are man-
made.

• 3. The sea: The sea’s water is salty. Seas are the
largest water source on earth. Though drinking salty
water in large quantities is usually harmful to
humans, it is possible to drink sea water if it is first
treated in a desalination plant. Desalination means
getting rid of the salt in sea water.
• 4. Rainwater: Rainwater are usually safe to drink,
though in the cities rainwater can be contaminated
by the pollutants found in vehicle and factory fumes
rendering it highly acidic. Nevertheless, rainwater is
an abundant source of water for watering plants and
crops.

• 5. Wells: Water from wells tends to be very
fresh and clean, and they have been a source
of water for many centuries.
• 6. Reservoirs: Reservoirs are like artificial
lakes created by humans to collect either
rain water or river water. The water in a
reservoir is typically treated in a water
treatment plant until it is safe to drink.

• Water for drinking purposes must be safe and
wholesome. A safe and wholesome water is a one
which is:
• • Free from pathogens
• • Free from harmful chemical substances
• • Pleasant to taste (i.e. free from odor and color)
• • Usable for domestic purposes.
• Water is said to be ‘contaminated’ when it contains
pathogens or harmful chemical substances and it is
said to be ‘polluted’, when it contains substances or
impurities affecting the physical quality of water
such as color, odor, taste and turbidity.

Purification of water

• Purification of water
• (A) Purification of water on a large scale:
method of t/t depends upon the nature of
raw water & desired standards of water
quality. Components:
• a) Storage
• b) Filtration removes 98-99% of bacteria.
• c) Disinfection

• a. Storage: Water is impounded in natural or
artificial reservoirs. This natural
purification offers many advantages viz:
 Physical:.
Chemical:
Biological:

 Physical: About 90% of suspended impurities settle
down in 24 hrs by gravity. Water becomes clearer &
allows better penetration of light & reduces the work of
filters.
 Chemical: Aerobic bacteria oxidize the organic matter
with the aid of dissolved oxygen which reduces free
ammonia & raises the nitrate level.
 Biological: tremendous drop occurs in bacterial count (
>90% in first 5-7 days for river water). Optimum
recommended period for storage of river water is 10-14
days. Longer period of storage results in growth of algae
imparting bad colour & taste to water.

b. Filtration:
1. Slow sand filter / Biological filter
2. Rapid sand filter / Mechanical filter
• Slow Sand or Biological filters: It has
following Elements:
• Supernatant raw water
• Bed of graded sand
• Under drainage system
• System of filter control valves

Slow sand filter

Slow sand filter
• The supernatant provides the driving force or constant
head for the water to overcome the resistance of filter
bed and provides waiting period of some hours for the
raw water to undergo sedimentation, oxidation and
particle agglomeration.
• A layer of graded gravel of about 30 - 50 cm thickness is
placed over the perforated pipes.
• Above the gravel is the sand bed having a thickness of
about 1-1.2 m. The sand grains have an effective
diameter between 0.2-0.3 mm.
• The under drainage system which is about 16 cm in
depth, consists of porous or perforated pipes which
serves the dual purpose of providing an outlet for
filtered water as well as supporting the filter media
above.

• A system of control valves facilitates the regulation of
filter rate and adjustment of water level in the filter.
• Shortly after the start of filtration, slow sand filter acts
primarily biologically by forming a slimy ‘zoogleal’ layer
also known as ‘Vital Layer’ or ‘Schumutzdecke (dirt
layer)’ on the sand bed.
• This layer is slimy and gelatinous and consist of thread
like algae and biological organisms like plankton,
diatoms and other minute plants and protozoa.
• They feed on the organic matter and convert it into
simple harmless substances.
• The vital layer which is also the heart of the filter
removes organic matter, holds back bacteria & oxidises
ammonical nitrogen into nitrates & helps in yielding,
bacteria free water. Till the vital layer of the filter bed is
fully formed (called ripening of bed), the filtrate is run to
waste.

• The Filtration rate lies between 0.1- 0.4 m3
/hour/ per square meter removes organic
matter, holds back bacteria & oxidizes
ammoniacal nitrogen in to nitrate and removes
99.99% of bacteria but occupies a larger space.
• The major advantages are simple to construct
& operate, cheap to construct and the Physical,
chemical & bacteriological quality of water is
very high.

• Slow sand filtration is a type of centralised or
semi-centralised water purification system.
• A well-designed and properly maintained slow
sand filter (SSF) effectively removes
turbidity(waste) and pathogenic organisms
through various biological, physical and
chemical processes in a single treatment step.
• Only under the prevalence of a significantly
high degree of turbidity or algae-
contamination, pre-treatment measures (e.g.
sedimentation) become necessary.
• Slow sand filtration systems are characterised
by a high reliability and rather low lifecycle
costs.

Advantages
• Very effective removal of bacteria,
viruses, protozoa, turbidity and
heavy metals in contaminated fresh
water
• Simplicity of design and high self-
help compatibility: construction,
operation and maintenance only
require basic skills and knowledge
and minimal effort
• If constructed with gravity flow
only, no (electrical) pumps required
• Local materials can be used for
construction
• High reliability and ability to
withstand fluctuations in water
quality
• No necessity for the application of
chemicals
• Easy to install in rural, semi-urban
and remote areas, Simplicity of
design and operation
• Long lifespan (estimated >10 years)
Disadvantages
• Minimal quality and constant flow of
fresh water required: turbidity (<10-20
NTU) and low algae contamination.
Otherwise, pre-treatment may be
necessary
• Cold temperatures lower the efficiency
of the process due to a decrease in
biological activity
• Loss of productivity during the
relatively long filter skimming and
ripening periods
• Very regular maintenance essential;
some basic equipment or ready-made
test kits required to monitor some
physical and chemical parameters
• Possible need for changes in attitude
(belief that water that flows through a
green and slimy filter is safe to drink
without the application of chemicals),
Chemical compounds (e.g. fluorine) are
not removed
• May require electricity
• Requirement of a large land area, large
quantities of filter media and manual
labour for cleaning, Low filtration rate

b. Filtration:
• Rapid sand filter / Mechanical filter
• Comprises of Water+ alum mixing chamber(Alum – aluminium Sulftate to
treat watse water)
• flocculation chamber (Collection)
• sedimentation tank
• filter
• chlorine added
• clear water storage
• consumption.
• Rate of filtration is 5-15 m3 / m2/ hour (slow sand filter- 0.1- 0.4 m3
/hour/)
• Effective size of sand particle is 0.4-0.7mm
• Back washing is used for cleaning of filter.
• Treatment by chemical coagulation & sedimentation
• Before the water comes to the filter it is subjected to a process of coagulation
with alum.
• The filter bed is essentially similar to slow sand filter with two differences:

• The sand is coarser
• o The biological membrane in slow filter is replaced by a
layer of alum floc
• The rate of filtration in a rapid filter is 4000- 7500
liters per square meter as against 100 – 400 liters in a
slow sand filter .
• Removes 98-99% bacteria
• Occupies very little space
• Advantages: can deal with raw water directly, filter
beds occupy less space, filtration is rapid, washing of
filters is easy, more flexibility in operation

Chlorination of water
• Chlorination is the process of adding chlorine to
drinking water to disinfect it and kill germs.
Different processes can be used to achieve safe
levels of chlorine in drinking water. Chlorine is
available as compressed elemental gas, sodium
hypochlorite solution (NaOCl) or solid calcium
hypochlorite (Ca(OCl)2 While the chemicals could
be harmful in high doses, when they are added to
water, they all mix in and spread out, resulting in
low levels that kill germs but are still safe to
drink

Water Quality
• 1. Safe and wholesome water: defined as
water that is
• a. Free from pathogenic agents
• b. Free from harmful chemical substances
• c. Pleasant to taste
• d. Usable for domestic purposes
• % Population with access to safe water in
India: 85%

• 2. Biological water quality standards set out by WHO
• The WHO has set out the following criteria for water
quality:
• a. No sample should have E. coli in 100 ml.
• b. No sample should have more than 3 coliforms
(Bacteria) per 100 ml. ≤ 3
• c. Not more than 5% samples throughout the year
should have coliforms in 100 ml. (roundworms and
tapeworms)
• d. No two consecutive samples should have coliform
organisms in 100 ml.

• 3. Chemical water quality standards
• The WHO has set out three chemical quality standards:
• a. Toxic substances – The upper permissible levels of lead,
selenium, arsenic, cyanide, cadmium, and mercury are 0.01, 0.01,
0.01, 0.07, 0.003, and 0.001 mg / litre in domestic drinking water
• b. Substances that may affect health
• i. Fluorine should be present in a concentration of 0.5 – 0.8 mg/l
• ii. Nitrates should not exceed 45 mg/l
• iii. Polynuclear aromatic hydrocarbons should not exceed 0.2
micrograms per litre
• a. Substances that may affect water acceptability
• Upper permissible limits have been set out for a number of
substances like iron, calcium, chloride, sulphate, etc.

• Total hardness should not exceed 3 meq/ liter
• Turbidity <5 nephelometric turbidity units
• Chloride: 200mg / L
• Ammonia: Indicator of bacterial , sewage pollution,
compromises the disinfection ability by forming nitrites
• pH: Acidic water <7 pH causes elevated PH levels &>8 causes
chlorination to be ineffective
• hydrogen sulphide : prominent in ground water
• Iron: Ferric ion causes objectionable reddish brown colour
• Manganese: stains sanitary wares; forms coating on pipes

Test to determine Chlorine content of
water
• Orthotolidine test: estimates free and
combined chlorine together
• Orthotolidine- Arsenite test: estimates
free and combined chlorine separately.

c. Water disinfection
• The need for disinfection to prevent water
borne diseases and its inclusion as one of the
water treatment processes is considered
necessary.
• Disinfection of water means making it fit for
drinking by destroying all pathogenic
organisms that may be present in it:
• 1. Physical methods such as thermal
treatment and ultrasonic waves.
• 2. Chemicals including oxidising chemicals
such as chlorine and its compounds and ozone.
• 3. Radiation

• Chlorination: It is the most commonly used method. In
water treatment or purification practice, the term
disinfection is synonymous with chlorination.
• Disinfection of water is therefore, usually carried out by
the use of chlorine who fulfils all the criteria’s of good
disinfectant.
• When chlorine is added to water it forms hydrochloric
acid and hypochlorous acid. Hypochlorous acid further
dissociates into hydrogen ions (H+) and hypochlorite
ions
• (OCl-).
• Cl2+H2O=HCl + HOCl.
• HOCl = H++ OCl-

• The reaction is reversible. The disinfection
action of chlorine is mainly by hypochlorous
acid and partly by hypochlorite ion. Chlorine
acts best when pH of water is around 7
because of predominance of hypochlorous
acid.
• However, viruses , sporing organisms,
protozoal cysts, helminth ova, molluscs,
cyclops and cercariae are not affected by the
usual dosage.

• Chlorine demand: Chlorine and chlorine compounds by
virtue of their oxidizing power can be consumed by a
variety of inorganic and organic materials present in water
before any disinfection is achieved.
• It is therefore, essential to provide sufficient time and dose
of chlorine to satisfy the various chemical reactions and
leave some amount of unreacted chlorine as residual either
in the form of free or combined chlorine adequate for
killing the pathogenic organisms.
• The recommended concentration of free chlorine is 0. 5
mg/L for one hour. The difference between the amount of
chlorine added to water and the amount of residual
chlorine after a specified contact period (usually 60
minutes), at a given temperature and pH of water is
defined as ‘chlorine demand’.2/18/2020 59Mrs. Arpita Vaidya

• Breakpoint chlorination: The point at which the
free residual chlorine appears after the entire
combined chlorine residual has been completely
destroyed is referred to as breakpoint and the
corresponding dosage is the breakpoint dosage.
• The point at which chlorine demand of water is met
is called ‘breakpoint chlorination’.
• If chlorine is added further, it only increases free
chlorine. Usually the methods of chlorine
application is by the addition of a weak solution
prepared from bleaching powder, HTH etc. for
disinfecting small to medium quantities of water.
• It is simple, does not require electricity and
relatively safe but instability of bleaching powder, its
hygroscopic nature and low percentage of available
chlorine makes it difficult to reach desired levels of
free chlorine.

• Water Sterilizing Powder (WSP):
Bleaching powder is considerably improved
in its keeping quality by the addition to
quicklime in the proportion of 80 : 20 when
it is known as water sterilising powder. Its
available chlorine should not be less than 25
percent. WSP is usually used for disinfection
of water under field service conditions.

• Household purification of water
• i. Boiling: roll boiling for 5-10 minutes.
• ii. Bleaching powder: 33% of available chlorine.
• Stabilized bleach: bleaching powder+ excess lime
• iii. Chlorine solution: 4 kg bleaching powder+ 20 litres
water 5% chlorine solution.
• iv. Chlorine tablets: 0.5 g for 20 litres of water.
• v. Filtration: Chamberland filter, Berkfeld filter & Katadyn filter.
• vi. Disinfection of wells: Double pot method – to ensure constant
dosage of chlorine to well water in emergency situations; can be
left for 2-3wks containing 4500L of water with daily draw of 360
– 450L

Chamberland filter

• Hardness of water
• i. Bicarbonates of Ca & Mg: Temporary hardness
• ii. Sulphates of Ca & Mg: Permanent hardness
• iii. Fe, Mn, Al can all cause hardness
• Classification
• 1. Soft water - <1meq / L (<50 mg / L)
• 2. Moderately hard water – 1-3 meq / L (50 - 150mg
/ L)
• 3. Hard water – 3-6 meq / L (150 - 300 mg / L)
• 4. Very Hard water - >6 meq / L (>300 mg / L)

Methods used for removing hardness
of water are:
• i. Temporary hardness
• Boiling
• Addition of lime
• Addition of NaHCO3 (Sodium hydrogen
carbonate)
• ii. Permanent hardness
• Addition of Na2CO3 (Sodium carbonate)
• Base exchange

Sanitation:
• Sanitation is ‘the science of safeguarding the
health.’ The term environmental sanitation is
defined by WHO as, ‘the control of all those
factors in man’s physical environment, which
exert a deleterious effect on physical
development, health and survival’.

• Sanitation: conditions relating to public
health, especially the provision of clean
drinking water and adequate sewage disposal.

• Majority of communicable diseases in India are
due to poor environmental sanitation, i.e.
contamination of water, pollution of air, soil,
unhygienic disposal of sewage, refuse and
waste, infestation of insects, rodents, etc.
• Poor environmental sanitation supplemented
by social factors like
– poverty,
– illiteracy,
– ignorance,
– poor standard of living,
– over-crowding, etc.
– are mainly responsible for the increased morbidity
and mortality. Hence sanitation is crucial for the
prevention and control of infectious diseases.

Sanitation:
• Environmental sanitation envisages(Predict)
promotion of health of the community by providing
clean environment and breaking the cycle of disease.
• It depends on various factors that include
– hygiene status of the people,
– types of resources available,
– innovative and appropriate technologies according to
the requirement of the community,
– socioeconomic development of the country,
– cultural factors related to environmental sanitation,
– political commitment,
– capacity building of the concerned sectors,
– social factors including behavioral pattern of the
community,
– legislative measures adopted, and others.2/18/2020 71Mrs. Arpita Vaidya

• India is still lagging far behind many
countries in the field of environmental
sanitation. The need of the hour is to
identify the existing system of
environmental sanitation with respect to its
structure and functioning and to prioritize
the control strategies according to the local
needs.

What are the challenges for
maintaining optimal WASH?
• 1. Prevention of contamination of water in
distribution systems
• 2. Growing water scarcity and the potential for
water reuse and conservation,
• 3. Implementing innovative low-cost sanitation
system
• 4. Providing sustainable water supplies and
sanitation for urban and semi-urban areas
• 5. Sustainability of water and sanitation
services.

1. Prevention of contamination of
water in distribution systems

2. Growing water scarcity and the
potential for water reuse and
conservation,

3. Implementing innovative low-cost
sanitation system

Conventional Pit Latrine- low cost

The World Toilet Organization (WTO)

4. Providing sustainable water
supplies and sanitation for urban
and semi-urban areas

5. Sustainability of water and
sanitation services.

Solid Waste & Solid Waste
Management
• Solid wastes include rubbish or materials that are
not economically useful, present in solid, liquid or
gaseous form, which originate from a wide range of
human operations, such as industry, commerce,
transport, agriculture, medicine and domestic
activities.
• The output depends on various factors like the
degree of urbanization, dietary habits, lifestyles and
living standards.
• In most of the countries the per capita daily solid
waste produced is between 0.25 to 2.5 Kg. With the
rise in urbanization, land areas available for filling
are getting lesser and lesser.

But there is a huge impact if this
solid waste is not disposed of
properly like:
• Leads to Contamination of ground water and
Surface water
• Waste decomposes and favours fly breeding,
attracts rodents and pests
• Aesthetically unpleasant and generates foul
odour
• Generation of inflammable gas such methane
and greenhouse gases inside the waste dump

Waste decomposes and favours fly
breeding, attracts rodents and pests

Aesthetically unpleasant and
generates foul odour

Generation of inflammable gas such
methane and greenhouse gases
inside the waste dump

Classification of Solid wastes:
• (a) Refuse could be generated from street
sweepings, markets, stable litter comprising of
animal droppings and left-over feeds, industrial
refuse ranging from inert to toxic and explosive
compounds and commercial refuse from retail
stores, hotels, warehouses and offices.

• (b) Rubbish a general term applied to solid
wastes originating in houses,
establishments & institutions, excluding
garbage and ash. It includes paper, clothing,
bits of wood, metal, glass, dust and dirt.

Classification of Solid wastes:
• (c) Ash is the residue from burning of wood,
coal, charcoal, coke and other combustible
materials used for cooking and heating
purposes in domestic, commercial and
industrial establishments. Ashes consist of a
fine powdery residue, cinders often mixed
with small pieces of metal and glass.

• (d) Garbage is a term used to describe
animal and vegetable wastes resulting from
the handling, storage, sale, preparation,
cooking and serving of food. It contains
organic matter, which decomposes to emit
foul odour and hence requires urgent
disposal.

• Classification of Solid Waste
• Solid waste can be classified into different types depending on
their source:
• Household waste or municipal waste: includes food,
paper, cardboard, plastic, textiles, leather, glass, metal,
ashes, electronics waste etc.
• Industrial waste: includes toxic chemicals, oil, debris from
construction site, packaging waste, ashes etc.
• Biomedical waste or hospital waste: medicine bottles,
expired medicines, syringes, medical instruments such as
scissors, blades etc
• Agriculture waste: includes pesticides, crops, water
coming from the fields also consists of small amount of toxic
chemicals.
• Nuclear waste: includes radioactive substances coming
from reactors, fuel (uranium, thorium, plutonium etc). Its
highly dangerous and requires proper disposal.
• Hazardous waste: includes toxic corrosive, ignitable and
reactive materials etc.

• Types of waste according to properties
• Bio-degradable can be degraded (paper,
wood, fruits and others)
• Non-biodegradable cannot be degraded
(plastics, bottles, old machines, cans,
containers and others)

• Solid Waste Management should be
compatible with following principles
• Improve public health – decrease in diseases
• Enhance environmental well-being – to
ensure more hygienic and pollution-free
• Better living conditions
• Use of effective use of technologies for
adaptation to cost-effective and
• Environmentally clean technology

• Functional Elements of the Waste Management System:
There are six functional components of the waste
management system as outlined below:
• 1. Waste generation refers to activities involved in
identifying materials which are no longer usable and are
either gathered for systematic disposal or thrown away.
• 2. Onsite handling, storage, and processing are the
activities at the point of waste generation which
facilitate easier collection. For example, waste bins are
placed at the sites which generate sufficient waste.
• 3. Waste collection, a crucial phase of waste
management, includes activities such as placing waste
collection bins, collecting waste from those bins and
accumulating trash in the location where the collection
vehicles are emptied. Although the collection phase
involves transportation, this is typically not the main
stage of waste transportation.

• 4. Waste transfer and transport are the activities
involved in moving waste from the local waste
collection locations to the regional waste disposal
site in large waste transport vehicles.
• 5. Waste processing and recovery refer to the
facilities, equipment, and techniques employed both
to recover reusable or recyclable materials from the
waste stream and to improve the effectiveness of
other functional elements of waste management.
• 6. Disposal is the final stage of waste management. It
involves the activities aimed at the systematic
disposal of waste materials in locations such as
landfills or waste-to-energy facilities.

No use of plastics

No use of plastics
• Plastics and their role in waste disposal: Plastics are organic
polymeric materials that can be transformed into desired shapes
by different industrial processes. These may contain natural
elements such as natural rubber, cellulose or synthetic elements
such as polythene or nylon.
• Plastics have excellent thermal and electrical insulation
properties and good resistance to acids, alkalis and solvents.
• Plastics are widely used in commercial and industrial sectors
such as packaging industry, building, motor manufacturing and
consumer goods industry.
• However, these plastics are not easily destroyed during waste
management processes and are poorly biodegradable. Moreover,
the chlorinated plastics emit toxic gases when thermally treated.
Plastics are known to clog or choke water lines, sewers or storm
water drainage systems.

• UNIT 4: Basics of Epidemiology and Disease
Surveillance

Unit overview:
• This unit provides an introduction to key
concepts, methods and topics in
epidemiology, as well as some of the statistical
methods required to be able to appreciate
and appraise epidemiological research. The
course focuses on applied aspects of
epidemiology in an interactive environment
conducive to adult learning and integrating
epidemiologic principles with the other
streams in public health.

Learning Objectives
• Upon completion of this course, participants will be able to:
• 1. Define and describe the common terminologies used in
epidemiology.
• 2. Comprehend the basic concepts and approaches of
epidemiology.
• 3. Apply the analytical skills to solve a given epidemiological
problem or situation.
• 4. Conceptualize the relationship between epidemiology
and other disciplines of public health.
• 5. Design epidemiological studies, based on the strengths
and weaknesses of different epidemiological methods, to
answer questions of public health practice.
• 6. Orientation to Disease Surveillance

Suggested Readings:
• Text Book of Epidemiology by Leon Gordies
• Text Book of Epidemiology & Biostatistics by
Bonita and Beeglehole

Definition:
• Epidemiology is defined as “The study of the
frequency, distribution and determinants of
diseases and health - related states and
events in human populations” and the
application of this knowledge in prevention,
control and mitigation (Improvement) of
these problems.

• the branch of medicine which deals with the
incidence, distribution, and possible control of
diseases and other factors relating to health.

Epidemiology and Disease
Surveillance
• It is derived from a Greek word:
• Epi = upon,
• Demos = populations,
• Logos = scientific study.
– The major purpose of epidemiology is to obtain,
interpret and use health information to
promote health and reduce disease in a
community.

• Epidemiology or Epidemiologist uses the same
tools and techniques as clinical medicine or
clinician, with few following major differences :
• ● In clinical practice the focus is on an
individual, the patient; however, in
epidemiology, the focus is on a group of human
beings (patients or healthy people) which we
refer to as “population”.
• ● In clinical practice we focus more on
diseased person based on diagnosis, but in
epidemiology the findings are analyzed after
converting them into meaning observations by
“summarizing the findings and using them for
further prevention of disease.

Epidemiology or Epidemiologist uses the same tools and
techniques as clinical medicine or clinician, with few
following major differences :
• In clinical practice the
focus is on an individual,
the patient
• In clinical practice we
focus more on diseased
person based on diagnosis
• however, in epidemiology,
the focus is on a group of
human beings (patients or
healthy people) which we
refer to as “population”.
• but in epidemiology the
findings are analyzed after
converting them into
meaning observations by
“summarizing the findings
and using them for further
prevention of disease.

Uses of Epidemiology:
1. It helps to study the natural history of a
disease, i.e. in relation to agent, host and
environmental factors and further evolution
of the disease to its termination as death or
recovery, in the absence of prevention or
treatment. This is a necessary framework for
application of preventive measures.

Malaria epidemiological triad

2. It helps to measure the disease frequency in
terms of the magnitude of the problem (i.e.
morbidity and mortality rates).
3. It helps to make ‘Community diagnosis’ by
studying the distribution of the disease with
reference to time, place and person.
Therefore, epidemiology has been considered
as ‘Diagnostic tool’, in community medicine.
4. Descriptive epidemiology helps to formulate
an ‘etiological hypothesis’.

• 5. It helps to identify the determinants of the
disease and the risk factors.
• 6. It helps to study historically the rise and
fall of the disease in the population, i.e. As
old diseases are conquered (e.g. Polio
/Smallpox) new diseases have been identified
such as (Swine flu, HIV , EBOLA etc.).
• 7. It helps to estimate the individual’s risk of
a particular disease by using the indices like
Absolute risk, Attributable risk, Relative risk,
Odd’s ratio, etc.
• 8. It helps to identify syndromes, e.g. AIDS etc

• 9. It helps to formulate the ‘plan of action’ for
providing the health services including preventive
and control measures.
• 10. It helps to ‘evaluate’ the health services to
find out whether the measures undertaken are
effective in controlling the disease or not. Further it
also helps to find out the cost-effectiveness of
different methods.
• 11. It helps to make researches in epidemiology.
• 12. It contributes to the standardization of bio
statistical techniques.

Epidemiology studies:

Epidemiology studies:
• Broadly Epidemiological studies are of two types—
observational and experimental.
1. Observational Studies
• Here, the studies are based on the field observations, They are of
two types namely descriptive and analytical studies.
• a) DESCRIPTIVE STUDIES
• These are concerned with observation of the distribution of a
disease in a community, with reference to time, place and
person, and identifying the associated characteristics of the
disease to formulate an etiological hypothesis.
• b) ANALYTICAL STUDIES
• This is also an observational study of epidemiology which deals
with testing the etiological hypothesis, formulated by
descriptive epidemiological study (i.e. to confirm the
determinants of the disease.)

a) DESCRIPTIVE STUDIES
• These are concerned with observation of the distribution of a disease in a community,
with reference to time, place and person, and identifying the associated characteristics
of the disease to formulate an etiological hypothesis.
• Steps:
• a) Defining the population under study: This means specifying the type of population
under study, i.e. if it is the entire population of the area, or a representative sample or a
group of population like urban / in slums / only females / only adults / only children,
industrial workers, pregnant mothers, etc. The population is also be defined in terms of
area (place) and time. For example, if we want to study the problem of leptospiroisis:
then we define it as in South Gujarat , during a given year, the population under study is
all and the time is the particular year. Hence, the study population (defined population)
becomes the population at risk, i.e. it becomes the denominator and helps in calculating
the rates, i.e. in measuring the disease frequency.
• b) Defining the disease under study: That means the disease which is taken up for study
has to be defined in such a way that the epidemiologist should be able to identify BOTH
those with disease from those without the disease, and should also be able to measure it
with validity. For example, leptospirosis patient is defined as a patient with PCR positive
for sero var of Lepotospirosis.

c) Describing the distribution of the disease with
reference to time, place and person.
• TIME DISTRIBUTION: This means describing the
time of occurrence/onset of the disease with
reference to year, month, week, day, hour of onset,
season, atmospheric temperature, climate etc. This
study often gives a clue about the etiology of the
disease or the predisposing factors, so that
preventive measures can be adopted.
• There are three kinds of time trends or fluctuations:

• 1. Short-term fluctuations: This means sudden occurrence of a
disease in a given area, and lasting for a short period, e.g. an
epidemic disease.
• 2. Periodic fluctuations.: This means occurrence of a disease in a
community during a definite period, either in a particular
season or periodically in a cyclic form. Accordingly, there are
two types: Seasonal trend (in a specific season eg. Leptospirosis
is seen in rainy season) and cyclic trend (tendency of a disease
to occur cyclically once in several days, weeks, months or years.
Examples: Epidemic of measles once in 2 to 3 years)
• 3. Long-term fluctuations: This means changes in the occurrence
of the disease over a long period of time, several years or
decades. For example, Non Communicable diseases upward
trend in India in last 20 years.

• PLACE: This means the pattern of occurrence of a
disease in different places. This helps to compare the
disease occurrence from one District to another District
or from one state to another state, from rural to urban
areas and local areas. It can also compare the occurrence
from one country to another country.
• PERSON DISTRIBUTION: This means describing the
distribution of a disease in the community with
reference to the host characters of the persons affected,
such as age, sex, occupation, literacy level, marital status,
social class, behavior, and such other factors.

• Types of Descriptive study:
• Descriptive studies deal with the distribution of disease/health
condition. There are a number of different descriptive methods:
• 1. Case reports: Single observation by a clinician which
prompts further investigations with a more rigorous study
design. Eg. Use of OCP as observed by one clinician that leads to
Benign Ca was case reporting which later led to case control
study with proven casual relationship between the same.
• 2. Case series: A case series aggregates individual cases in one
report. Sometimes several such cases within a short period may
lead to an alarm for an impending epidemic e.g. A cluster of
homosexual mans in North America with similar sign sand
symptoms had alarmed the world of a disease which today is
known as AIDS.

3. Cross sectional & Longitudinal

• 4. Ecological Co relational studies:
• This is studies done to look the association between
exposures and outcomes in population rather than
the individuals. As much data has already been
collected, these studies are suitable only for initial
search of hypothesis. The biggest drawback of such
studies is that their inability to link exposures to
outcome in individuals (this phenomenon is called
ecological fallacy and is defined as ascribing to
the members of the group characteristics that
they in fact do not possess as individuals) and to
control the confounders.

• Uses of Descriptive Epidemiology
• • It helps to know the extent/magnitude of the
disease in the community, in terms of
• morbidity and mortality rates.
• • It helps to know the distribution of the disease
with reference to time, place and person.
• • It helps to identify the risk group.
• • It helps to formulate an etiological hypothesis.
• • It helps to plan, organize and implement curative
and preventive services.
• • It helps in doing research.

• b) ANALYTICAL STUDIES
• This is also an observational study of
epidemiology which deals with testing the
etiological hypothesis, formulated by
descriptive epidemiological study (i.e. to
confirm the determinants of the disease.)
There are two types of analytical studies:
• 1. Case-control study.
• 2. Cohort study.

• These studies can show:
• • Whether any association exists between the
suspected factor and the disease of the
hypothesis.
• • If so, what is the strength of the association
between the suspected factor and the disease
under study.

• 1. Case control study:
• It is a study between the two groups, one group of
persons having a particular disease under study
called ‘Cases’ and another group of persons called
‘Controls’ who are all comparable with cases in
respect of age, sex, literacy level, occupation, marital
status, socioeconomic status but free from the
disease under study. The control group is taken for
the purposes of comparison of observations. Study
is now made by obtaining information from each
member of both the groups, about the exposure to
the suspected factor made in the hypothesis.

• Bias case control study:
• Bias is any systematic error that occurs during any stage
of the study, thereby resulting in mistaken estimate of
exposure and/ or outcome. A case control study is more
prone to bias as compared to a cohort study. Although
included as a bias confounding is not a systematic error
in measurement, it is a true phenomenon existing in
nature.
• • Memory or recall bias: Since it is a retrospective study,
the recall of events can be better among the cases than
controls, more so, sometimes in cases also the history of
exposure can be in very past and hence less likely to be
remembered.
• • Selection bias: This occurs when the selected sample does
not represent the universe or whole population from
which it is drawn.

• • Confounding bias: Since the confounding factor itself
independently can result in the disease, care must be
taken while selecting the controls that they must be free
from the confounding factors also. This can be avoided
by robust matching.
• • Berksonian bias: This occurs specially in the hospital
based studies because the patients with different
diseases will have different rates of admission to
hospitals. This bias is named after Joseph Berkson, who
was the first person to recognize this problem.
• • Interviewer’s bias: This occurs when the interviewer
knows who is in the study group and who is in the
control group. So the interviewer asks questions
thoroughly to the cases then controls, regarding the
history of exposure to the suspected cause.

• Advantages of case control studies
• i. Relatively quick and easy to undertake.
• ii. Relatively cheap to undertake.
• iii. Only method useful in rare diseases.
• iv. Not enmeshed in problems of follow-up as the
data is collected at one point in time.
• v. Can be used to study the effect of many
exposure variables on a single disease outcome.

• Disadvantage of case control studies
• i. Prone to selection and recall bias.
• ii. Can’t measure relative risk or provide incidence
estimates. (Only odd’s ratio can be calculated from the
type of study, which is a rough estimate of relative risk.
But when the disease in question is a rare one odd’s
ratio is almost equal to relative risk)
• iii. Sometimes the occurrence of the exposure in terms
of time, i.e. whether it occurred before the disease
may be difficult to estimate.
• iv. Can’t be used for rare exposures.

• 2. Cohort Study:
• The literal meaning of the term ‘cohort’ refers to a group that shares
similar characteristics.
• a. Cohort studies are FORWARD LOOKING; look for the development of
disease in a group of individuals (the cohort) free of the same at the
beginning.
• b. The group is followed up over a period of time. During this period some
persons will develop the disease under study while others will remain free
of the disease (FOLLOW-UP STUDY).
• c. The characteristics (and exposure to disease causing factors) are
compared between those who suffer from disease and those free from
the disease.
• d. Thus, in cohort study, identified groups of populations who are free of
the disease being studied and who are similar in all respects, except the
specific exposure variable or characteristic whose effect is being related to
the disease being studied. These groups are then followed up for the
period of time that it takes for the disease to develop.
• e. A cohort study can either be prospective or retrospective but unless
otherwise specified it is assumed to be prospective in design, but a case
control study is always retrospective.

• When to select a cohort design?
• The cohort design should therefore be
undertaken when:
• • Disease a reasonably common one,
• • Short follow-up is required and the cohort
can be followed for a considerable time.
• • Enough evidence is present regarding the
association between exposure and outcome
• • The attrition (drop-out) is not high.

• Advantages of cohort study:
• i. Can calculate the incidence rate and hence relative risk can be
computed.
• ii. Temporality of association can be established.
• iii. Can be used to study multiple outcomes of one type of exposure.
• iv. It helps to estimate the relative risk and attributable risk.
• v. It allows the assessment of dose-response relationship.
• vi. It helps to accept or to refute the hypothesis with a high degree of
validity.
• Disadvantagesof cohort studies:
• I. Cohort studies are expensive, time consuming and difficult.
• II. Unsuitable for investigating uncommon diseases.
• III. Certain administrative problems are inevitable such as lack of
experienced staff, lack of funds, etc.
• IV. Attrition (reduction) in the size of the cohort or control group can
occur due to death or migration or dropouts etc.
• V. It involves ethics (People cannot be deliberately kept under the
influence of the potentially harmful factor).

• EXPERIMENTAL STUDIES
• They are generally classified into two types:
randomized controlled trial and field trials or
community trials. Randomized controlled trials are
usually undertaken to prove the efficacy of any
therapeutic agent or efficacy of any preventive
interventions or efficacy of any procedure which is
tested on any individual subject. However, in a field
trial or a community trial, a large group of person as
a whole are used to determine the efficacy of any
drug or procedure or any intervention.

• Association in analytical studies:
• a. Risk and its measurement: - Risk is measured to help to: -
• i. Prevent the disease. (Risk = incidence measure of disease).
• ii. Predict incidence and prevalence of disease
• iii. To help diagnose the disease
• iv. To help to establish the cause of the disease of unknown etiology.
• b. Measurement of RISK: -Absolute risk
• i. Relative risk
• ii. Attributable risk
• iii. Odds ratio
• iv. Population attributable risk
• Absolute risk is incidence of disease in the population. Eg. incidence of
Lung cancer.

Disease Difference between Case
control and Cohort study

Other concepts in Epidemiology
• Health
• Health is defined (by WHO) as ”A state of complete
physical, mental and social well-being of an individual
and not merely an absence of disease or infirmity
(infirmity = weakness, feebleness, opposite of
firmness).”
• WHO’s definition of health is criticized for-
• 1. Cannot be defined as a state
• 2. Non-measureable
• 3. its generality, particularly what is meant by
wellbeing;
• 4. health dynamics and spiritual human health are not
captured

Social Determinants of Health :
• The social determinants of health are mostly responsible for
health inequities - the unfair and avoidable differences in health
status seen within and between countries.
• Employment conditions :
• Social exclusion :.
• Public health programmes and social determinants :
• Women and gender equity :
• Early child development :
• Globalization :
• Health systems :
• Measurement and evidence :
• Urbanization :

Disease
• Disease is "any deviation from or
interruption of the normal structure or
function of any part, organ, or system (or
combination thereof) of the body that is
manifested by a characteristic set of
symptoms and signs. "Hence the term
disease can be termed as :

• An interruption, cessation, or disorder of body
functions, systems, or organs;
• Morbid entity characterized usually by at
least two of these criteria:
– recognized etiologic agent(s),
– identifiable group of signs and symptoms, or
consistent anatomical alterations.
• Literally disease, the opposite of ease, when
something is wrong with a bodily function."

Tools of epidemiological
measurement

Tools of epidemiological
measurement
• a) Rate : In epidemiology, rate is a measure
of the frequency with which an event
occurs in a defined population over a
specified period of time.
• b) Ratio : A ratio is the relative magnitude
of two quantities or a comparison of any
two values. It is calculated by dividing one
variable by the other. The numerator and
denominator need not be related.

Method for calculating a ratio
Number or rate of events, items, persons, etc. in
one group
Number or rate of events, items, persons, etc. in
another group

• Proportion : A proportion is the Number with
disease (numerator) at a point in time Number
in population (denominator)
• Method for calculating a proportion
• Number of persons or events with a particular
characteristic x 10n
• Total number of persons or events, of which
the numerator is a subset

Indicators of health
• Since health is not defined in measurable
terms and since health is multidimensional
and is never static,
– health is measured multi dimensionally,
– and we use appropriate Health Indicators to
measure the status of the health of the
community.

• Uses of health indicators:
• To measure the health status of a country
• To compare the health status of one
country with that of another country
• To assess the health care needs
• To plan and implement health care
services
• To evaluate the health care services.

Classification of indicators:
• These indicators are classified as follows:
• Mortality indicators
• Morbidity indicators
• Disability rates
• Nutritional status indicators
• Health care delivery indicators
• Utilization rates
• Indicators of social and mental health
• Socioeconomic indicators
• Health policy indicators
• Environmental indicators
• Indicators of quality of life

Mortality indicators
• Crude death rate (CDR): It is defined as number of deaths per 1000 population,
per year, in a given area. It indicates the rate at which people are dying. Higher the
crude death rate, poorer is the health status of a country. A decrease in CDR
indicates overall improvement in the health of the population.
• Infant mortality rate (IMR): It is defined as the number of deaths of infants per
1000 live births, during a given year in a given population/country. It is a very
comprehensive indicator, a sensitive indicator and the most important indicator of
health because it reflects not only the quality of maternal and child health services
but also the availability and utilization of the services.
• Maternal mortality rate (MMR): This also indicates the quality of services
provided to mothers of reproductive age group, i.e. antenatal, natal and postnatal
services.
• Child mortality rate: It is the number of deaths of children between 1 to 4 years,
during a given year per 1000 mid-year population of that age group. This excludes
infant mortality.
• Under 5 proportional mortality rate: It is the proportion or percentage of total
deaths occurring among the children below 5 years of age. This includes both infant
mortality and child mortality rates. High rate indicates poor health status.
• Proportional mortality rate: The proportional mortality rate of communicable
diseases means the percentage of total deaths due to communicable diseases is an
useful indicator because it indicates the magnitude of preventable mortality.

Morbidity indicators
• These reveal the burden of diseases in a
community. Thus, these are used to
supplement the mortality rates.
• Incidence rate: It is the number new cases of
a particular disease occurring per 1000
population in a year.
• Prevalence rate: It is the total number of
both old and new cases existing in the
population during a given period or time. It is
expressed in percentage, i.e. percentage of the
population suffering from a particular disease.

Disability rates
• It is the percentage of the population, unable to perform
the routine expected, daily activities due to injury or illness.
Disability rate quantifies the seriousness of the disease.
• The disability rates are divided into two groups:
• 1. Event type indicators:
• Number of days of restricted activity
• Bed disability days
• Work loss days (or school loss days) (sickness absenteeism).
• 2. Person type indicators:
• Limitation of mobility (confined to bed or to house)
• Limitation of daily activity.

• Sullivan’s index: This is computed by subtracting the duration
of bed disability (during life) from the expectation of life at birth.
This is one of the recent indicators.
• Health adjusted life expectancy (HALE): It is the number of
years a newborn is expected to live in full health, based on
current morbidity and mortality. This term HALE was previously
known as DALE (Disability adjusted life expectancy).
• Disability adjusted life year (DALY): It is the number of
years lost in the healthy life of an individual due to disability.
One DALY is ‘one lost year of healthy life’. It is a measure of the
burden of disease in a defined population and the effectiveness
of the interventions. Even though it is a valid indicator of health,
its use is limited because of the non-availability of essential data.

Nutritional status indicators
• These are:
• Obese & Over nourishment
• Incidence of low birth weight
• Weight and height standards of children up
to 5 years.

Healthcare delivery indicators
• Focuses on the available health care delivery
indicators against total population
• Doctor: Population 1:2,500
• Nurse: Population 1:5,000
• Health worker: Population 1:3,000
• Pharmacist: Population 1:10,000
• Lab technician: Population 1:10,000
• Sub-centers: Population 1:3,000

Utilization rates
• It is the proportion (percentage) of the people
actually utilizing the health care services, in a
given population during a given year. For eg.
Proportion of infants ‘Fully immunized’ /
Proportion of expectant mothers, who have received
‘Adequate antenatal care’ etc
• These indicators not only indicate the availing of
health care services but also indicates whether the
need was felt or not, whether there was rapport
between the provider and the consumer and also the
accessibility and the acceptability of the services.

• Indicators of social and mental health
• These include the rates of crimes, assault,
murder theft, suicides, homicides, accidents,
juvenile delinquency, prostitution, gambling,
drug-abuse, lock-out of industries etc.
• Socioeconomic indicators
• • Per capita income; Gross national product
(GNP)
• • Percentage of people below poverty line
• • Level of unemployment
• • Per capita calorie availability

• Health policy indicators
• These are the proportion of the budget (GDP)
(gross domestic product)spent on health
services and health related services such as
water supply, sanitation, nutrition, housing,
community development, etc.
• Environmental indicators
• These reflect the quality of physical and
biological environment. These include the
indicators relating to pollution of air, water,
noise, radiation, solid waste, etc. eg. % houses
receiving safe water supply / status etc

• Quality of Life indicators
• PQLI : It is the Physical Quality of Life Index and is based
on three indicators- infant mortality, life expectancy at
age one and literacy. It does not take per capita GNP into
consideration and ranges from 0-100 with 0 given to
worst performance and 100 to best.
• HDI (Human Development index) : It is the index
combining three indicators-
– life expectancy at birth,
– knowledge (mean year of schooling and expected year of
schooling) and
– income (GNI per capita or purchasing power parity). It
ranges between 0-1.

Relationship between prevalence and
incidence

Natural history of disease

Epidemiological triad

• According to this model, disease occurs when the equilibrium
between agent, host and environment is disturbed. Thus, this
model explains that some persons do not suffer from the disease
even though they harbor the pathogens because an equilibrium
is established between the causative agent and the host.
• a) Agent factors :
– a) Physical agents:
– b) Chemical agents:
– c) Mechanical agents:
– d) Nutritional agents:
• b) Host Factors: These are the factors in the individual which
determine the outcome of the interaction among three factors.
These includes Age , Gender , Occupation, Literacy level , Marital
status and Income:
• c) Environmental Factors:
– Physical environment: Air, water, soil, food, etc.
– Biological environment: Plants, animals, insects, rodents, microbes,
etc.
– Psychosocial environment:

Epidemic
• a. The occurrence of a disease clearly in
excess of normal expectancy is called an
epidemic.
• b. In an area where a disease has not been
seen for many years, even the occurrence of
a single case may be sufficient to call it an
epidemic.
• c. To call a disease as an epidemic it must be
more than 2SD of previous year.

Types of epidemic:
• a. Common source epidemic: -
• i. Single exposure: -
– All cases within one incubation period
– Epidemic curve rises and falls rapidly
– No secondary waves
– Clustering of cases within narrow interval of time eg. Bhopal Gas tragedy
• ii. Continuous or Multiple Exposure: - Exposure is multiple eg. CSW and Legionnaires d/s in
Philadelphia
• b. Propagated epidemic
– i. Results from person to person transmission eg. Polio epidemic
– ii. Gradual rise and fall in epidemic curve over a period of time.
– iii. Spread of d/s depends upon the herd immunity, opportunities for contact and SAR
• c. Slow (modern) epidemic: -
• i. Secular trend
• If the pattern or trend of disease frequency changes only over many years then it is called a secular
trend. A secular trend implies a consistent tendency to change in a particular direction or a definite
movement in one direction. Eg: Coronary heart disease, lung cancer & diabetes which have shown a
consistent upward trend in the developed countries over the past 50 years.
• ii. Cyclic trend
• If the occurrence of disease changes over a short duration of time like a year, it is called a cyclic
trend.
• Some diseases change in frequency over seasons and such changes are referred to as seasonal
changes – Measles and chickenpox are examples of such diseases.

Endemic diseases
• The constant, continuous or usual presence of a
disease in a defined geographic area or delimited
territory is called an endemic disease.
• i. Hyper endemic refers to a persistent intense
transmission in an area ( Hyperendemicrefers to
persistent, high levels of disease occurrence.
Occasionally, the amount of disease in a community
rises above the expected level.)
• while Holoendemic means a disease staring early in
life and affecting most of the Population.
• An endemic disease may become an epidemic if the
number of cases usually seen suddenly increase in
proportion like Malaria, tuberculosis, leprosy,
filariasis, etc.2/18/2020 Mrs. Arpita Vaidya 179

• Endemic: A characteristic of a particular
population, environment, or region.
• Examples of endemic diseases include
chicken pox that occurs at a predictable rate
among young school children in the United
States and malaria in some areas of Africa.

Cases
• a. Primary case
• The first case of a disease which occurs in a
community/area is called the primary case. In
disease like acute conjunctivitis a number of
primary cases may occur almost at the same
point in time in such case the primary cases are
referred to as “Co–primaries”
• b. Index case
• The first case, which comes to the attention of
the health authorities in an area, is referred to as
the index case. Such a case may or may not be
the primary case.

Secondary attack rate:
• The secondary attack rate refers to the number of cases
occurring among contacts of a primary case within the
known incubation period of the disease.
• The denominator refers to the number of susceptible
contacts who are in close touch with the primary case.
However, if a person among the contacts has previously
suffered from the specific disease and developed
immunity is not known, then all the contact should be
considered in the denominator.
• No. of individuals developing disease within one
incubation period
• SAR = -----------------------------------------------------------------
--------- X 100 Total no. of susceptible in close contact

Herd immunity
• i. The immune status of a group of people/community
is called herd immunity as it is the immune status of
the ‘herd’ of people. (by the immunization)
• ii. For many communicable diseases, an outbreak of
disease is only possible if the level of immunity is
sufficiently low and there are a large number of
susceptible in the population.
• iii. In diseases like poliomyelitis, diphtheria, measles
etc., herd immunity plays an important role.
• iv. However, in a disease like tetanus or rabies where
every individual is at risk unless specifically protected,
herd immunity plays no role.

• Nosocomial infection
• i. An infection occurring in a patient in a hospital or
other health-care facility and in whom it was not
present or incubating at the time of admission or
arrival at a healthcare facility is called a nosocomial
infection. It refers to diseases transmitted from a
hospital.
• ii. Usually such infections are more difficult to manage,
as they are generally resistant to most of the common
antibiotics.
• iii. Nosocomial infections also include those infections,
which were contacted in the hospital but manifested
after discharge, and also infections suffered by staff
members if they contacted the infection from the
hospitalized patients.

Period of communicability
• i. Period of communicability or
communicable period refers to the time
during which an infectious agent may be
transferred directly or indirectly from an
infected person to a susceptible person.
• ii. This period is usually equal to the
maximum known incubation period for
that disease.

Contact transmission
• When disease is spread by direct contact with
an infected person, it is called contact
transmission. This may be by kissing, touching,
biting or sexual intercourse. Ringworm,
scabies, yaws, etc.

Zoonoses
• An infectious disease transmissible under natural
conditions from vertebrate animals to man is
called a zoonoses.
• i. Anthropozoonoses: Disease transmitted from
ANIMALS TO MAN. Eg. Rabies, Plague, Anthrax
• ii. Zooanthroponoses: Disease transmitted from
MAN TO ANIMALS. Eg. Human TB in cattle
• iii. Amphigenesis: Disease transmitted from MAN
TO ANIMALS and also ANIMALS TO MAN. Eg.
Schistosomiasis, Trypanosoma cruzi

• 10. Exotic: Disease imported into a country
• 11. Epizootic: Epidemic of disease in an
animal population, e.g. anthrax, brucellosis,
rabies, influenza etc
• Enzootic: Endemic occurring in animals, e.g.
anthrax, rabies, brucellosis, bovine
tuberculosis endemic tick typhus etc.

12. Quarantine: is the restriction of activities of healthy
persons (HEALTHY CONTACTS) or animals who have been
exposed to a communicable disease or are traveling from a
disease-endemic-zone to a non-diseased-area for a period
of time equivalent to the LONGEST KNOWN INCUBATION
PERIOD of that specific communicable disease.
Eg. For TB Incubation period week, month or year
• 13. Isolation: Separation, for the period of
communicability of infected persons (CASES) or animals
from others in and in such places and under such
conditions, as to prevent or limit the direct or indirect
transmission of the infectious agent from those infected to
those who are susceptible, or who may spread the agents
to others.

• 14. Disease control:
• 1. In disease control, the disease "agent" is
permitted to persist in the community at a level
where it ceases to be a public health problem. The
term "disease control" describes (ongoing)
operations aimed at reducing:
• i. the incidence of disease
• ii. the duration of disease, and consequently the risk
of transmission
• iii. the effects of infection, including both the
physical and psychosocial complications; and
• iv. the financial burden to the community.

• 15. Disease elimination:
• Between control and eradication, an intermediate goal has been
described, called "regional elimination". The term "elimination" is
used to describe interruption of transmission of disease, as for
example, elimination of measles, polio and diphtheria from large
geographic regions or areas. Regional elimination is now seen as an
important precursor of eradication.
• 16. Disease eradication:
• Eradication literally means to "tear out by roots". Eradication of
disease implies termination of all transmission of infection by
extermination of the infectious agent. As the name implies,
eradication is an absolute process, and not a relative goal. It is "all
or none phenomenon". The word eradication is reserved to
cessation of infection and disease from the whole world.

• 17. Prevention and levels of prevention :
• Prevention is the action aimed at eradicating, eliminating or minimizing the
impact of disease and disability, or if none of these are feasible, retarding the
progress of the disease and disability.
• a) Primordial prevention: Primordial prevention, a relatively new concept, is
receiving special attention in the prevention of chronic diseases. For example,
many adult health problems (e.g. obesity, hypertension) have their early
origins in childhood, because this is the time when lifestyles are formed (for
example, smoking, eating patterns, physical exercise).

• Primary prevention: Primary prevention can be
defined as the action taken prior to the onset of disease,
which removes the possibility that the disease will ever
occur. It signifies intervention in the pre-pathogenesis
phase of a disease or health problem. Primary
prevention may be accomplished by measures of “Health
promotion” and “specific protection”. It includes the
concept of "positive health", a concept that encourages
achievement and maintenance of "an acceptable level of
health that will enable every individual to lead a socially
and economically productive life". Primary prevention
may be accomplished by measures designed to promote
general health and well-being, and quality of life of
people or by specific protective measures.

Approaches for Primary Prevention: The WHO has recommended the
following approaches for the primary prevention of chronic diseases where
the risk factors are established
• a. Population (mass) strategy – “Population
strategy" is directed at the whole population
irrespective of individual risk levels. For example,
studies have shown that even a small reduction in
the average blood pressure or serum cholesterol of a
population would produce a large reduction in the
incidence of cardiovascular disease. The population
approach is directed towards socio-economic,
behavioral and lifestyle changes
• b. High -risk strategy: The high -risk strategy aims
to bring preventive care to individuals at special
risk. This requires detection of individuals at high
risk by the optimum use of clinical methods.

• Secondary prevention: It is defined as “action which halts the
progress of a disease at its incipient stage and prevents
complications.”
• The specific interventions are: early diagnosis (e.g. screening
tests, breast self-examination, pap smear test, radiographic
examinations, case finding programme, etc.) and adequate
treatment.
• Tertiary prevention: It is used when the disease process has
advanced beyond its early stages. It is defined as “all the
measures available to reduce or limit impairments and
disabilities, and to promote the patients’ adjustment to
irremediable conditions.” Intervention that should be
accomplished in the stage of tertiary prevention are disability
limitation, and rehabilitation.

• Incubation Period: The time between
entry of an agent into succeptible host and
appearance of visible signs and symptoms.

Iceberg phenomenon :
• The pattern of disease encountered in a hospital is quite
different from that in a community. In the
community/society a far larger proportion of disease (e.g.,
diabetes, hypertension) is hidden from view of the general
public or physician. In this context the analogy of an iceberg
is widely used to describe the disease pattern in the
community. The concept of the "iceberg phenomenon of
disease “gives an idea of the progress of a disease from its
sub-clinical stages to overt or apparent disease state. The
submerged portion of the iceberg represents the hidden
mass of the disease (e.g., subclinical cases, carriers,
undiagnosed cases). The floating tip represents what the
physician sees in his practice/chamber/hospital etc. The
remaining Large Hidden part of the iceberg is what
constitutes the mass of unrecognized disease in the
community.

Hills criteria of causality
• 1. Strength: A small association does not mean that
there is not a causal effect. Greater is the strength
more is the association.
• 2. Consistency: Consistent findings observed by
different persons in different places with different
samples strengthens the likelihood of an effect.
• 3. Specificity: Causation is likely if a very specific
population at a specific site and disease with no
other likely explanation. The more specific an
association between a factor and an effect is, the
bigger the probability of a causal relationship.
• 4. Temporality: The effect has to occur after the
cause (and if there is an expected delay between the
cause and expected effect, then the effect must occur
after that delay).

Hills criteria of causality
• 5. Biological gradient: Greater exposure should generally lead
to greater incidence of the effect. However, in some cases, the
mere presence of the factor can trigger the effect. In other cases,
an inverse proportion is observed: greater exposure leads to
lower incidence.
• 6. Plausibility: A plausible mechanism between cause and effect
is helpful (but Hill noted that knowledge of the mechanism is
limited by current knowledge).
• 7. Coherence: Coherence between epidemiological and
laboratory findings increases the likelihood of an effect.
However, Hill noted that "... lack of such [laboratory] evidence
cannot nullify the epidemiological effect on associations"
• 8. Experiment: "Occasionally it is possible to appeal to
experimental evidence"
• 9. Analogy: The effect of similar factors may be considered

Disease surveillance:
• Disease surveillance is an information-based activity involving the
collection, analysis and interpretation of large volumes of data
originating from a variety of sources. The information collated is then
used in a number of ways to:
• Evaluate the effectiveness of control and preventative health
measures
• Monitor changes in infectious agents e.g. trends in development of
antimicrobial resistance
• Support health planning and the allocation of appropriate resources
within the healthcare system.
• Identify high risk populations or areas to target interventions
• Provide a valuable archive of disease activity for future reference.
• To be effective, the collection of surveillance data must be standardized
on a national basis and be made available at local, regional and national
level. IDSP is one such effort in forecasting and responding to disease
outbreaks and incidents of local, regional and national significance.

Thank you

WASH & EPIDEMIOLOGY

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