This document provides an overview of key concepts in epidemiology including basic tools of measurement, rates, ratios and proportions. It discusses disease transmission dynamics including reservoirs, modes of transmission, and susceptible hosts. It also covers principles of disease prevention at different levels from primordial to tertiary. Additional topics include disease cycles, levels of prevention, disease control methods, and concepts like disinfection and sterilization.

1. UNIT-5
PRINCIPLES OF EPIDEMIOLOGY AND METHODS
By-Mandeep kaur

2. BASIC TOOLS OF MEASUREMENT IN EPIDEMIOLOGY
• MORTALITY
• MORBIDITY
• DISABILITY
• NATALITY
• ATTRIBUTES OF DISEASES- PRESENT OR ABSENT
• MEDICAL NEEDS
• HEALTH CARE FACILITIES
• UTILISATION OF HEALTH SERVICES
• ENVIRONMENTAL FACTORS SUSPECTED OF CAUSING DISEASE
• PSYCHOSOCIAL ASPECT OF HEALTH

3. RATE
• A rate measures the occurence of some particular event in a population during
a given time period.
• For example-Death rate, Birth rate, Specific rate.
• ELEMENTS OF RATE-
• Numerator
• Denominator
• Time specification
• Multiplier
EXAMPLE-Mortality
rate, Morbidity rate.
Crude Death Rate=No. of deaths in one yearx1000
Mid year Population

4. RATIO
• Ratio express a relation in size between two random quantities.
• Ratio is the result of dividing one quantity by another.
A:B OR A/B
ELEMENTS-Numerator, Denominator
For example- Ratio of available health services to utilization of health services
• Ratio of W.B.C to R.B.C
• Sex ratio
• Child women ratio

5. PROPORTION
• It is also a ratio indicates the relation in magnitude of a part of the whole. It is
expressed as a percentage.
• ELEMENTS-Numerator, Denominator and Percentage as multiplier.
• For example-Proportion of scabies among children in a given / certain time is
expressed as--
The number of children with scabies at a certain time
x 100
The total number of children in village at the same time

6. USES OF EPIDEMIOLOGY
• Epidemiology has wider application covering the areas such as disease, health and health
services. According to Thrushfield, there are 5 use of epidemiology. He is identifying the
6th use of epidemiology which is- To provide information to improve clinical decisions on
individual patient case management.
These 5 uses are as-
1. D etermination of the origin of a disease whose cause is known
2. Investigation and control of a disease whose cause is either unknown or poorly
understood.
3. Acquisition of information on the ecology and natural history of a disease.
4.Planning and monitoring of disease control programmes.
5. Assessment of the economic effects of a disease and analysis of the costs and economics
benefits of alternative control programmes.

7. • Morris has identified 7 uses of epidemiology are as follows-
1. To study the rise and fall of disease in the population
2. community diagnosis
3. Planning and evaluation
4. Evaluation of Individual's risk and chances
5. Syndrome indentification
6. Completing the natural history of disease
7. Searching for cause and risk factors.

8. DISEASE CYCLE
• The infectious agents enter the susceptible host after finding a
portal of entry such as respiratory tract, alimentary tract, skin
etc.
• Inside the human host on getting appropriate environment, it
multiply and distrub the health equilibrium and the disease
become overt.
• The host defense against the infection. If the host defense is
sufficient to suppress the disease , then recovery starts and if
insufficient then the patient develop the signs / symptoms of
disease and require treatment.

9. There are 6 stages of disease cycle which occur in human
host as described as below-
1. Incubation period
2. Prodromal period
3. Fastigium
4.Defervescence
5. Convalescence
6.Defection

10. INCUBATION PERIOD
It is defined as the time interval between the entryby an infectious
agent and appearance of the first sign and symptom of the disease.

11. PRODROMAL PERIOD
This period is of short duration, which ranges from one to four
days.The pathogenic agent multiply in human host and the vague
system appear .

12. FASTIGIUM
The symptoms are clear cut and are related to particular disease.
Disease can be identified by clinical diagnosis.

13. DEFERVESCENCE
The body's defence begin to respond and there is decline of
infection. The clients condition starts improving and feels better.

14. CONVALESCENCE
The improvement in the condition of patient occurs fast and the
recovery is established.

15. DEFECTION
The patient's condition is improved and comes to his pre illness
stage i.e is free from illness as the recovery has occured.

19. LEVELS OF PREVENTION
The goals of medicine are to promote health, to preserve health, to
restore health when it is impaired and to minimize suffering and
distress. The natural history of disease provides the basis for
community health intervention.A four level model for prevention or
intervention, based on the stages of disease which includes-
1.Primordial Prevention
2.Primary Prevention
3.Secondary Prevention
4.Tertiary Prevention

20. PRIMORDIAL PREVENTION
It is concerned with prevention of development of risk
factors in population groups in which they have not yet
appeared.
For Example-helping children to develop healthy lifestyle so
they do not develop adult health problems like obesity and
hypertension.

21. PRIMARY PREVENTION
It is true prevention.Primary prevention can be defined as
action taken prior to the onset of disease, which removes the
possibility that a disease will ever occur.
It includes-Health Promotion
Specific Promotion

22. HEALTH PROMOTION
By merely promoting the health of the
individual and community we can
prevent a number of diseases such as
typhoid fever, TB, cholera and
nutritional diseases.Health education is
the process of enabling people to
increase control over and to improve
health.

23. SPECIFIC PROMOTION
It comprises those measures which are
directed to intercept causative agents of a
particular disease or group of diseases
before these agents affect people.
EXAMPLE- Immunization against
poliomyelitis.
Vitamin A supplements to prevent
nightblindness.

24. SECONDARY PREVENTION
Secondary prevention means the action taken to halt the
progress of a disease at its incipient stage and also prevention
of complications.Secondary prevention focuses on the
individuals who are experiencing health problems and illness
and who are at risk for developing complications or
worsening conditions.
The goal is to cure disease at its earlier stage.The specific
interventions used are-
1.Early diagnosis and treatment
2.Referral

25. EARLY DIAGNOSIS AND TREATMENT
The disease complications can be
prevented and health can be restored by
diagnosing the disease at its early stages
and by providing the adequate treatment
according to the health problem.

26. Tertiary Prevention
According to human development report , tertiary
prevention is defined as all the measures available to reduce
or limit impairments and disabilities , minimise suffering
caused by exsiting departures from good health and to
promote the patient's adjustment to irremedial conditions.
Tertiary prevention includes-
1.Disability limitation
2.Rehabilitation

27. DISABILITY LIMITATION
The sequences of events in disability
are-
Disease----Impairment----Diability----
Handicap.
Disability interventions are aplied in
the late pathogenesis phase to
mnimize suffering and to promote
the patient's adjustment to
untreatable conditions.The objective
of it is to prevent the transition of
the disease process .

28. REHABILITATION
Acc to WHO rehabilitation is" The
combined and coordinated use of
medical, social, educational and
vocational measures for training and
retraining the individual to the highest
possible level of functional ability"
OBJECTIVES-To adopt all measures to
reduce the impact of disability and
handicapped.

29. • Rehabilitation can be achieved by physiotherapy, occupational therapy , speech therapy
, educational and vocational guidance etc.
• The various aspects of it are-
1. MEDICAL REHABILITATION-restoring and retraining the functional ability of an
individual. For eg-Teaching various exercises in physiotherapy department as in case of
polio.
2.VOCATIONAL REHABILITATION-means makina an individual capable to earn his
livelihood .For eg- training the blind and mentally retarded individuals to make candles or
weave the chair.
3.SOCIAL REHABILITATION-means restoring family and social relationship.this is achieved
when an individual starts participating actively in community life.
4.PSYCHOLOGICAL REHABILITATION-means restoring the dignity and confidence of
disabled and cripped individual.Guidance and counselling techniques can be used to
rehabilitate.

30. DYNAMICS OF DISEASE TRANSMISSION
It involves the chain of infection.
1.SOURCE OF RESERVOIR-Any person, animal, plant, soil or
substance in which an infectious agent normally lives and multiplies.
The reservoir typically harbors the infectious agent without injury to
itself and serves as a source from which other individuals can be
infected. The infectious agent primarily depends on the reservoir for
its survival. It is from the reservoir that the infectious substance is
transmitted to a human or another susceptible host.

32. DISEASE TRANSMISSION DIRECT AND INDIRECT
The disease is transmitted from the reservoir to susceptible host
either directly and indirectly by a single or several routes.The mode
of transmission of infectious agent is classified as-
1. Direct Transmission-When the disease is transmitted directly from
the source of infection to susceptible host.
2. Indirect Transmission -When the disease agent is transmitted
indirectly to susceptible host.

33. MODE OF TRANSMISSION
DIRECT TRANSMISSION
1.Direct contact
2.Droplet Infection
3.Contact with soil
4.Inoculation into skin
or mucosa
5.Transplacental(vertic
al)
INDIRECT TRANSMISSION
1.Vehicle borne-Water, food,
milk.
2.Vector borne-mechanical,
biological
3.Air borne-Dust,Droplet
nuclei
4.Fomite borne-soild linen
5.Unclean hands and fingers

34. DIRECT TRANSMISSION
1. DIRECT CONTACT-Infection may be transmitted by direct contact
from skin to skin, mucosa to mucosa, mucosa to skin of the same or
another person.e.g- skin to skin contact or by touching, kissing or
sexual intercourse. STD, AIDS, leprosy etc are transmitted by direct
contact.
2.DROPLET INFECTION-This is direct projection of a spray of droplets
of saliva during coughing, sneezing, speaking and talking into
surrounding atmosphere.eg-common cold, whoophing cough, TB,
many infection of nervous system.

35. 3. CONTACT WITH SOIL-This refers to accquiring a disease agent by direct
exposure of susceptible tissue to disease agent in soil, compost or
decaying vegetable matter .e,g hookworm larvae, tetanus etc.
4.INOCULATION INTO SKIN-The disease agent may be inoculated directly
into the skin or mucosa e.g- hepatitis B VIRUS through contaminated
needles and syringes and rabies virus through dog bite.
5.TRANSPLACENTAL TRANSMISSION-Disease agents can be transmitted
transplacentally.TORCH AGENT come in this category. T-Toxoplasma gondii,
R-Rubella virus, C-Cytomegalovirus, H-herpes virus.

36. INDIRECT TRANSMISSION
1.VEHICLE BORNE-Transmission of the infectious agents through the
agency of water, food(raw vegetables, food, milk),ice, blood, serum
plasma or biological products such as tissues and organs.Disease
transmitted through water and food include-diarrhoea, typhoid ,
cholera, food poisoning. Contaminated blood can cause hepatitis B,
malaria, syphilis.

37. 2. VECTOR BORNE-Vectors are intermediate living objects which may
spread the infection from one host to another.
Acc to involvement of vector and propagation of parasites, is of two types
as discussed below-
1.Mechanical transmission
2.Biological transmission
3.AIR BORNE-The airborne infections occur by droplet nuclei and by dust.
1. Droplet nuclei-They are tiny particles and remain in air for long period
of time. These are easily drown from air into the lungs and retain there
causing a disease. Example- TB, Influenza, chicken pox.

38. .(b)DUST-is the larger droplet particles which is released into air
during talking, coughing or sneezing etc. and settle down by their
sheer weight on floor, carpets, clothes, bedding, linen and become
part of the dust.Disease carried by infected dust include
streptococcal infection, pneumonia, TB, Q- fever.This is common
type of transmission in hospitals.
4. FOMITE BORNE-Fomites are inanimate particles or substance
other than water or food contaminated by the infectious
discharges from a patient and capavble of transferring the
infectious agent to a healthy person.Disease transmitted by
fomities include diptheria, typhoid fever, eye and skin infections.

39. 5. UNCLEAN HANDS AND FINGERS-Hands are the most common
medium by which pathogenic agents are transferred to food from
the skin, nose etc.as well as from other foods.Examples include
diptheria, typhoid fever, eye and skin infections.

40. SUSCEPTIBLE HOST
A susceptible host is a member of a species population who is at risk
of becoming infected with a certain disease due to a variety of
reasons. Susceptible hosts differ from the general population
because they are far more likely to get infectious diseases than the
general population.Examples of risk factors include poor personal
hygiene, poor control of infection throughout the environment and
the age of the host. These factors all contribute to the host's ability
to become easily infected with a disease when exposed.

41. CONTROL OF INFECTIOUS DISEASE
Each disease has certain weak points susceptible to attack.The basic
approach in controlling disease is to identify these weak points and
break the weakest links in the chain of transmission.This require
knowledge of disease that is its magnitude, distribution in time,
place and person,source of infection and dynamics of transmission.
The control of disease implies mainly the prevention of
disease.Disease control is a continuous process, it involves following
measures-

42. 1. CONTROLLING THE RESERVOIR
(a)EARLY DIAGNOSIS-It is needed to treat patients, trace the source
of infection, to study distribution of disease and apply control
measure.
(b)NOTIFICATIONS-Local health authority should be notified, so that
it can implement control measures.
(c)EPIDEMIOLOGICAL INVESTIGATIONS-It is done to identify source
of infection such as climate socio-cultural and behavioural related to
spread of infection.

43. (d) ISOLATION-It is defined as -Separation for the period of
communicability of infected person or animals from others in such
places under such conditions , as to prevent or limit the direct or in
direct transmission of the infectious agent from those infected to
those who are susceptible or who may spread the agent to others.
(e)TREATMENT-using effective drugs cuts short duration of disease
and interrupts its transmission.
(f)QUARANTINE-means freedom of movement of such well persons
or domestic animals as exposed to communicable disease for a
period of time not longer than the longest incubation period of
disease.

44. 2.INTERRUPTION OF DISEASE
It consists of preventing infective agent from entering the body of a
susceptible host by purifying water, many water borne disease can
be prevented e.g like typhoid, cholera can be prevented.
If transmission is through vectors, vector control measure will help
to prevent transmission of disease such as by destroying mosquito
breeding places , malaria, filaria and dengue can be prevented.

45. 3. IMMUNIZATION OF THE SUSCEPTIBLE HOST
Immunization strengthens the susceptible host , thereby, chain of
transmission of communicable disease is broken.Immunization
produces immunity by which body develops or receives antibodies
to fight against specific disease.
The government of India has recommended National Immunization
schedule to protect infants, children and pregnant women from
various communicable disease.

46. 4.CHEMOPROPHYLAXIS
It means protection from or prevention of disease using
chemotherapeutics.
EXAMPLE-Prevention of clinical symptoms of cholera by tetracycline
or furazolidine for household contacts.

47. 5.NON SPECIFIC MEASURES
Such measures as im provement of general sanitation, nutritional
status and education have an important role in controlling and
preventing disease.
The objectives of disease control are-
a)Reducing the incidence of disease
b)Decreasing the duration of illness
c)Decreasing the possible complications.
d)Decreasing the mortality and morbidity.

48. DISINFECTION
1.DISINFECTANT-is an agent which kilss infectious agents outside the body
by direct exposures to the chemicals.
2.DISINFECTION-Killing of infectious disease out of the human bodyby use
of chemicals
3.ANTISEPTIC-An antiseptic is an agent which destroys the growth of
infectious agents, which can be applied on living body e.g-dettol or alcohol.
4.Deodorant-is an agent which suppresses bad odour.e.g-lime or bleaching
powder.

49. DISINFECTION
5.DISINFECTATIONS-ANy physical or chemical process which destroys
bacteria, disease spreading germs or vector and vehicles of disease such as
insects, parasites, rodents and animals.
6.STERILIZATION-Destruction of microrganism and their spores.
7.Detergent-Asurface cleansing agent which act by lowering surface tension
e.g-soap, which removes bacteria with dirt.

50. TYPES OF DISINFECTION
1.CONCURRENT
DISINFECTION-Infectious
organism is destroyed
as soon as discharged
from infectious person.
3.PROPHYLACTIC
DISINFECTION-Use of
disinfective measures to
prevent spread of infection
such as boiling of water ,
hand washing etc
2.TERMINAL INFECTION-
Use of disinfective
measures after removal
of body of diseased
person

51. TYPES OF DISINFECTION
NATURAL DISINFECTANTS-1.Sunlight
2.Air
PHYSICAL DISINFECTANTS-1.By heat
2.Moist Heat 3. Radiation
CHEMICAL DISINFECTANTS-1.Liquids
2.Solids 3.Gases

52. TYPES OF DISINFECTION
1.NATURAL AGENTS-
(a)SUNLIGHT-Direct exposure to sunlight is an effective measure for killing
infective organisms.Therefore bedding furniture etc are exposed to strong
sunlight for longer period for disinfection.
(b) AIR- act by drying or evaporating the moisture which helps to breed the
bacteria causing infection.
2.PHYSICAL AGENTS-
(a)BURNING-Inexpensive articles, useless articles such as rags, used
dressings material can be disposed of by burning.Needles too can be
sterlized by burning for 3 seconds.

53. DISINFECTION
2.BOILING-in
water for at least
20 mts. helps to
disinfect the
articles like
needles, rubber
gloves etc.
4.STEAM UNDER
PRESSURE-attains
deep penetration hence
disinfection destroys
bacteria and their
spores.It is used in
hospitals and laboratory
practices.
3.PASTEURIZATION
-It is used for
sterlization of
endoscorphic
instruments, which are
heated upto 80dg.C
for 20 mts.

54. STREAM UNDER PRESSURE
(a)AUTOCLAVE-
(b)PRESSURE COOKER
3.CHEMICAL AGENTS-The articlesw which cannot be sterlized by autoclaving
can be sterlized by chemicals.
Classified as follows-

55. 1.
•PHENOL AND RELATED COMPOUNDS
•Phenol, Cresol, Cresol emulsions,Dettol
2.
•DETERGENTS
•Soap, Cetrimide,Savlon
3.
•HALOGENS
•Chlorines.Iodine,Iodopers

56. 4. Oxidising
agents
5.Miscellaneous-
Alcohol,Methylted
spirit,Formalin.

57. CHEMICAL DISINFECTION AGENT
pp
1.PHENOL AND RELATED
COMPOUNDS
1.PHENOL-is a cheap and
effective disinfectant.It is
used in hospitals or for
domestic purposes is a
crude
phenol(phenol+cresol).It is
effective against vegetative
gram+ and -bacteria.
2.CRESOL-It is an
excellent coal tar
disinfectant. 5to10% cresol
is used to disinfect faces,
urinals, spectrum etc.It is
also used with other
compoundswhich are
known as lysol, izal and
cyllin called cresol
emulsions.
3.DETTOL-It is used for
sterilizing instruments and
plastic tins.It is a highly
effective antiseptic against
gram + bacteria.

58. CHEMICAL DISINFECTION AGENT
OTHER LIQUID CHEMICAL AGENTS-
1.DETERGENTS-Soap, Savlon-Clinical thermometer can be disinfected in 1.6
savlon solution,
Cetrimide-can be used in cleaning wounds
2.HALOGENS-Chlorines,Iodine,Iodopers
3.OXIDISING AGENTS
4.MISCELLANEOUS-Alcohol, Methylated Spirit,Formalin

59. CHEMICAL DISINFECTION AGENTS(SOLID)
1
1.LIME-This is sprinkled in public places
where open area filled with urine or faeces.
2.BLEACHING POWDER-Used as
purification agents of water, deodorant for
removing foul smell and odour.
3.POTASSIUM PERMAGANATE-It
is used for mouth wash and as disinfectant in
cleaning of fruits and vegetables.

60. CHEMICAL DISINFECTION AGENTS(GASES)
1
1.FORMALDEHYDE-Gas is used for
disinfecting the room. when the room is
filled with gas it is closed for 12 hours for
full disinfection.Disinfection of books, bed,
blankets can be done this way.
2.ETHYLENE OXIDE-has been used
in sterilizing plastic eqipments, cardiac
catheters etc.