Epidemiology is the study of disease patterns in populations and the factors that influence these patterns. The document discusses several key aspects of epidemiology including: 1. Epidemiology studies both healthy and sick people to determine what distinguishes those who get a disease from those who don't. 2. Descriptive epidemiology describes disease patterns in terms of person, place, and time, while analytic epidemiology investigates relationships between exposures and disease occurrence. 3. Epidemiologists play important roles such as determining disease causes and distributions, aiding in public health planning, and recommending prevention and control measures.

2. Introduction : The essential role of epidemiology is to improve the
health of populations. the epidemiologists tend to use the 5 W's:
diagnosis or health event (what), person (who), place (where), time
(when), and causes, risk factors, and modes of transmission (why/how).
What is Epidemiology?The word epidemiology comes from the
Greek words epi, meaning on or among, demos, meaning people, and
logos, meaning the study of.
Introduction to
Epidemiology

3. 
Epidemiology is the study of frequency, distribution, determinants and
dynamics of diseases or health conditions in a defined population and the
application of this study to control of health problems
Epidemiology: the study of factors influencing the occurrence, transmission,
distribution, prevention and control of disease in a defined population
Definitions of
Epidemiology

4. 
Epidemiology Clinical medicine
Unit of study is defined population Unit of study is a case
The concern is in the disease pattern
in the population
The concern is in the disease in
the patient
The investigator goes out to the
community
The patient comes to the doctor
Using tables and graphs to diagnose Using clinical picture and
laboratories
Seeks etiology to recommend control
and prevention
Seeks a diagnosis to give
treatment to patients
Epidemiology and Clinical
medicine:

5. 
1-Epidemiologists study sick and healthy.people
2-To determine the crucial difference between
those who get the disease and those.who are spared
3-Epidemiologists study exposed or non-
exposed people.
4-To determine the crucial effect of the exposure
Epidemiologists Role

6.  •To determine, describe, and report on the natural of disease, injury, and
death
•To aid in the planning and development of health services and programs
•To study the cause (or etiology) of disease(s), or conditions, disorders,
disabilities, etc.
•To determine the primary agent responsible or ascertain causative factors
•To determine the characteristics of the agent or causative factors
•To determine the mode of transmission
•To determine contributing factors
To identify and determine geographic patterns
Uses of epidemiology

7. 
Two major types:
Types of Epidemiology
•Descriptive epidemiology
•Analytic
epidemiology

8.  Define frequency and distribution of disease in
population and observing the basic feature of its
distribution in terms of place, person and time ( ppt)
The Epidemiologic Triangle for descriptive studies:
•Descriptive
epidemiology
Person
Place
Time

9. •Person •Geographic Place •Time
•Age, Gender, Ethnic Group
•Genetic Predisposition
•Concurrent Disease
•Diet, Physical Activity,
Smoking
•Risk Behavior,, Occupation
•presence of agents or
vectors
•climate -geology
•population density
•economic development
•nutritional practices
•medical practices
•calendar time
•time since an event
•physiologic cycles
•age (time since
birth)
•seasonality
•temporal trends
.

10. 
Analysis of determinant of health problem and
Investigating a hypnosis about the relationship of disease
to specific cause.
The Epidemiologic Triangle for analytic
epidemiology: three characteristics that are examined to
study the cause(s) for disease;
•Host * Agent
Environment
•Analytic epidemiology
Host •Agen
t
•Environment

11. •Host •Agents •Environment
•Personal traits
•Behaviors
•Genetic
predisposition
•Immunologic factors
•Biological Physical
•Chemical
•Influence the chance
for disease or its
severity
•External conditions
•Physical/biological/soci
al
•Contribute to the
disease process
cont,.

12.  *Host, agent and environmental factors are not in balance
due to
•new agent
•*change in existing agent (infectivity, pathogenicity,
virulence)
•*change in number of susceptible in the population
•*environmental changes that affect transmission of the
agent of growth of the agent
Epidemics occur when

13. 
1. *often concentrate on PPT
 *demographic distribution
 *geographic distribution
 *seasonal patterns and temporal trends
 *frequency of disease patterns
1. *are built around the analysis of the relationship between
• exposures
• *disease occurrence
1. *are built around the analysis of differences between
 cases
 *healthy controls
•Epidemioogic Activities

14. 
 Introduction
A key feature of epidemiology is the measurement
of disease outcomes in relation to a population at
risk. The population at risk is the group of people,
healthy or sick, who would be counted as casas if
they had the disease being studied.
Measurements in
Epidemiology

15. 
.
Basic Measurements in
Epidemiology
•Measurements of
mortality.
•Measurements of
morbidity.
Measurements of disability
Measurements of medical needs

16. 
•Rate: is the measure of the change of quantity per unit of time.
•E.g. If there are 2000 new-born infant in Ismailia in 2013 and
during this year 80 died the proportion of deaths = 80/2000=
0.04 = 40 per 1000
When express this proportion per time it becomes a rate, e.g. the death rate
in this group = 40 per year
Tools of Measurements
•Ratio: The simplest relation in numbers, degree or quantity
existing between two similar things
•e.g. there are 20 male students and 30 female students in
classroom ( the ratio of males to females in classroom is 2:3 or
2/3 or (20 ♀ : 30 ♂)
•Proportion or percent: it’s the explanations of the relationship
between two numbers where one of them ( the numerator) and the
other( denominator) e.g students in classroom = 50 students ; the
proportion of males = 20/50= 0.4 or 0.40%

17. 
•Mortality is the incidence of death
•Mortality statistics is a part of a system of vital records (fact
collected and presented in numerical from and derived from record
of vital events birth, death and migration)
•Measures of Mortality
Mortalityratesandratios:
•Annual death rate
•Crude death rate.
•Specific death rates.
•Disease specific death rate - Age specific death rate
•Sex specific death rate - Income specific death rate
Proportional mortality rate.

18. 
•General mortality rate ; a population group exposed to
risk of death and a time period
1-Annual death rate:
2- Crude death
ratethe number of deaths occurring in that population during that period of time.
Does NOT account for differences of age, sex, etc. in any aspect of death.

19. 
= the number of deaths due to specified cause per
100,000 midyear
3- Cause Specific death rate
•Measurements of Morbidity
•Incidence
•Prevalence
•Attack
rate

20. 
•Theincidenceofadiseaseistherateatwhichnewcasesoccurina
populationatriskofdevelopingthatdiseaseduringaspecifiedperiod
•Incidence rate:
Prevalence rate
: is the number of total cases of diseased (or affected) persons in a population
at a specific time divided by the number of population at that time

21. 

1. Verify the diagnosis of the disease by:
•Laboratory investigation of the disease.
•Clinical criteria of the disease.
•Epidemiological criteria of certain outbreaks may be added.
2. Confirm the existence of an epidemic
•Collect data about diagnosed cases.
•Look for unrecognized or unreported cases.
•Determine the population at risk that may develop the disease.
•Compare the incidence of the disease in population.
Investigation of Epidemic
Steps of conducting the investigation:

22. 
. Describe the characteristics of the disease as:
Person: determine the characteristics as regards age, sex, occupation,
life style, social and cultural levels.
Time ; it is used to construct an epidemiological curve that is a graph
to illustrate the distribution of cases by date of onset in
hours, days, weeks or months.
Place: Plot for epidemic map (geographic coordinate chart).
4. Develop hypothesis:
that can explain the occurrence of that epidemic and the
distribution of observed cases.
5. Test the hypothesis:
Demonstrate difference in attack rates in exposed and non
exposed individuals to source of infections.
6. Formulate a conclusion:
based upon obtained evidence and results of the hypothesis
testing.
7. Implement: appropriate control measures and management of
cases.
Cont,.

23. 
Definition:
Screening
It is a strategy used in a population to identify the possible presence of an
undiagnosed disease in individuals without signs or symptoms by application
of tests, examinations or other procedures which can be applied rapidly
Typesofscreening
•Mass screening: means screening of the whole population (e.g.,
checking all infants for hearing problems)
•Selective screening (e.g. by age and sex: mammograms for women
aged over 40)
•Prescriptive screening: for early detection of disease in apparently
healthy individuals which can be better controlled if it is detected
early

24. (A) Criteria of the disease:
•Should be important one.
•Should be common enough to warrant a search for its risk
factors and latent stages.
•The morbidity and mortality of the untreated conditions
must be substantial.
•An effective treatment must exist and should be more
beneficial when applied to the pre symptomatic stage.
Criteria of screening
program

25. 
(B) Criteria of the test:
•Should be accepted by the population and suitable for
application.
•Should be easy, inexpensive, quickly done and free from
hazards.
•Sufficiently sensitive to detect disease during the
asymptomatic stage.
C) Criteria of the screened populations:
•Agreement should be obtained from people who will be
screened.
•Patients will benefit from further investigations and
treatment
High prevalence of the disease to justify screening.
Cont,.
Example of: Women and men aged 16 – 44
Screening
•Hypertension
•CA cervix
•Tuberculosis
Sexual transmitted disease (STD)

26. 
For persons who need to carry out
surveillance activities but have little prior
experience or training
Also helpful for people who would like to
better understand the process and reasoning
behind surveillance methods and
interpretation
Surveillance

27. 
#Concept of surveillance
epidemiologic surveillance is “ongoing systematic
collection, analysis, and interpretation of health data
essential to the planning, implementation, and
evaluation of public health practice, closely
integrated with the timely dissemination of these
data to those who need to know.”
Surveillance

28. 
 Collecting data is merely one step
 Critical goal is to control and/or prevent diseases
 * Any data collected must be organized and
carefully examined
 * Any results need to be communicated to public
health and medical communities
Why Is Surveillance
Important?

29. 
Vital to communicate results
 -During potential outbreak so public health and
medical communities can help with disease
prevention and control efforts
 -During non-outbreak times to provide information
about baseline levels of disease
 -Baseline provides information to public health
officials monitoring health at community level,
serves as reference in future outbreaks
Cont,

30. 
 Monitoring disease trends
 Describing natural history of diseases
 Identifying epidemics or new syndromes
 Monitoring changes in infectious agents
 Identifying areas for research
 Evaluating hypotheses
 Planning public health policy
 Evaluating public health policy/interventions
Surveillance information
has many uses

31. 
 Evaluating impact of national vaccination campaigns
 Identifying AIDS when unknown syndrome
 Estimating impact of AIDS on US health care system
in 1990s (using mathematical models based on
surveillance data)
 Identifying outbreaks of rubella and congenital
rubella among Amish and Mennonite communities
in 6 states in 1990 and 1991 (3)
 Monitoring obesity, physical activity, other
indicators for chronic diseases
Examples of uses of
surveillance data:

32. 
Classified as passive or active
 Passive surveillance: local and state health
departments rely on health care providers or
laboratories to report cases of disease
 -Primary advantage is efficiency: simple and requires
relatively few resources
 -Disadvantage is possibility of incomplete data due
to underreporting
 -Majority of public health surveillance systems are
passive
Surveillance Systems

33. 
 Active surveillance: health department contacts
health care providers or laboratories requesting
information about conditions or diseases to
identify possible cases
 -Requires more resources than passive surveillance
 -Useful when important to identify all cases
 -Example: between 2002 and 2005, active surveillance
used to detect adverse events associated with
smallpox vaccine. (2)
Cont,

34. 
Surveillance data allow description and
comparison of patterns of disease by person,
place, and time
Several ways to describe and compare
patterns, from straightforward presentations
to statistically complex analyses
Will concentrate on simple techniques
How to Conduct
Surveillance

35. 
 When available, demographic characteristics such as
gender, age, race/ethnicity, occupation, education
level, socio-economic status, sexual orientation,
immunization status can reveal disease trends
 Example: looking at Streptococcus pneumoniae, a
common cause of community-acquired pneumonia
and bacterial meningitis, examining distribution of
cases by race provides important information about
burden of disease in different populations
How to Conduct
Surveillance

36. 
 Table 1 shows data
collected on
Streptococcus
pneumoniae from
CDC Emerging
Infections Program
Network, a
surveillance program
that collects data from
multiple counties in 10
US states (4)
How to Conduct Surveillance:
Person – Numbers and Rates

37. 
Definitions:-
•Infection: is an invasive of the body by pathogens or microorganisms (or parasite) capable of
producing disease, or may not lead to disease.
•Infectious diseases are caused by pathogenic microorganisms, such as bacteria, viruses,
parasites or fungi; the diseases can be spread, directly or indirectly, from one person to
another.
•Communicable disease is an illness due to a specific infectious (biological) agent or its toxic
products capable of being directly or indirectly transmitted from man to man, from animal to
man, from animal to animal, or from the environment (through air, water, food, etc..) to man.
•Endemic/Enzootic: The constant presence of a disease or infectious agent within a given
geographic area.
•Epidemic/Epizootic: The occurrence in an area of a disease or illness in excess of what may be
expected on the basis of past experience for a given population.
•Pandemic/Panzootic: A worldwide epidemic affecting an exceptionally high proportion of the
global population.
Infectious Diseases
(Epidemiology)

38.  Difference between infectious disease and
others
.
•Zoonotic diseases are infectious diseases of animals that can cause
disease when to transmitted humans.
•Disease – a pathological condition of body parts or tissues characterized
by an identifiable group of signs and symptoms.
Infectious disease Other diseases
•Two or more populations •Deals with one population
•A case is a risk factor (infection in one person can
transmitted to other)
•Risk case
•The cause often known •Identifies causes
The Epidemiological Triad of a Disease

39. •Host factors (Susceptibility):
•Heredity factor, Age, Sex, Occupation and Socioeconomic
conditions: income, occupation, residence
•Agent factors:
Agent may be (Biological , Physical, Chemical , Mechanical,
Nutritional, Genetic and Risk factors )
•Environment factor
•Internal environment eg. Diabetes
External environmental eg. Air, water, dust, metals& gases, :
animal, insects, microorganism, cultures, habits, tradition
.
This refers to a triad of ecological factors affecting the occurrence of
disease which may be related to: Agent, host & environment.
The interaction between agent, host and environmental factors that help to
maintain the presence of disease in the community.

40. 
An insect or any living carrier that transports an
infectious agent from an infected individual or its
wastes to a susceptible individual or its food or
immediate surroundings
Vector of infection

41. Definition of Infectious or epidemiological cycle :It is the process
through which an infectious agent is transmitted from source of infection to
new susceptible host.
Infectious process or cycle
(epidemiological cycle)
Infectious cycle:
1. Reservoir (source) of infection.
2. Modes of transmission.
3. Susceptible host.

42. 
Most infectious agents that cause disease are microscopic
in size (Bacteria, Viruses, Protozoa Fungi, Helminths
(Animals)
How Infectious Agents Cause Disease
•Production of poisons, such as toxins and enzymes, that
destroy cells and tissues.
•Direct invasion and destruction of host cells.
•Activating responses from the host’s immune system
leading to disease signs and symptoms.
Infectious Disease Agents

43. 
This refers to the source of infection in which the infectious agent
lives and multiplies
Source or Reservoir may be cases or carriers:
•Human reservoir (man): case or carrier
•Animal reservoir: (zoonosis).
•Non-living environment: soil, plant…… etc
Cases: Patients who show manifestations of the disease and are
infectious.
Carriers: Persons who carry the organism in their bodies but show no
signs or symptoms. The organisms are excreted with their discharges
and disseminate infection to others. .
(I): Source or Reservoir of
Infection ((

44. 
•1-Move freely in the community.
2. Clinically healthy (no signs or symptoms) and not known.
3. Large number exceeding the number of cases.
4. Sometimes infectivity period of carriers is very long
Importance of carrier
2)Modes of transmission (
Droplet (Air–borne) infection
Food–borne infection
Contact infection
Arthropod-borne infection
Fluids and blood modes of transmission

45. 
•Direct droplet: from the source to susceptible by direct contact e.g.
during coughing, sneezing, shouting, loud speaking, kissing
•Indirect method: through :
•Air borne droplet nuclei or dust.
•Contaminated articles & fomites.
•Milk: through invasion of the upper respiratory tract mucosa by the
organism in milk e.g. in case of diphtheria.
Example of droplet infections
•Bacterial: T.B., meningitis, diphtheria, pertussis, pneumonia.
•Viral: measles, mumps, rubella, chicken pox, influenza

Types of droplet
infections:

46. 
.
Predisposing factors of droplet
infection
•Overcrowding
•Bad ventilation
•Bad health
habits

47. 
•Direct (fecal-oral) transmission: through contaminated hands and fingers
by human or animal excreta (hand to mouth).
•Indirect (ingestion of contaminated food) through
•Vehicle transmission: contaminated water, ice, raw vegetables and fruits,
milk, meat, eggs, fish
•Vector transmission: mechanical transmission of organisms by house flies
and cockroaches.
•Use of human fertilizer lead to contamination of food (vegetables).
•Contaminated dust.
Examples of food borne infections
•Bacterial: cholera, typhoid, food poisoning, brucellosis.
•Viral: poliomyelitis, viral hepatitis
Parasitic: Ascariasis, amoebiasis, hydatid disease.
•Types of food borne
infections:

48. 
•Poor environmental sanitation e.g. food sanitation, water
sanitation, spread of insects.
•Lack of supervision of food places and food handlers.
•Bad health habits and lack of personal hygiene.
Predisposing factors
•Contact infection
•Organisms or parasites invade intact skin or mucous
membrane e.g. in Bilharziasis, syphilis, staph & strept.
Infection.
•Organisms invade injured skin or mucous membrane e.g. in
wound infection, tetanus, gas gangrene, rabies.

49. 
Arthropods or insects transmit infection by
•Mechanical transmission: the insect has no role in
multiplication or development of the organism.
•Biological transmission: the insect plays important
role in multiplication and development of the
organism to become infective.
•Arthropods borne
infection (vector – borne
diseases)

50. 
•Injection (parenteral) infection
•Blood transmitted infection through blood transfusion or
contaminated syringes or needles e.g. hepatitis B & C, AIDS,
syphilis, CMV.
•Pyogenic infections: By contaminated syringes & needles e.g.
staph injection.
•Vertical transmission: Form mother to fetus or infant: e.g.
hepatitis B & C, AIDS, syphilis.
•Through lactation ;( breast feedings) e.g. HBV, HCV, AIDS,
•Fluids and Blood modes
of transmission

51. 
An infectious agent seeks a susceptible host aiming
“successful parasitism‫التطفل‬”
The exposed host may be susceptible or not according to
his immunity.
Four stages are required for successful parasitism:
•*Portal of entry
•*Site of election inside the body
•*Portal of exit
*Survival in external environment
(3) Susceptible host (

52. 
Incubation period – time between infection and the
appearance of signs and symptoms
Prodromal phase – mild, nonspecific symptoms that
signal onset of some diseases.
Clinical phase – a person experiences typical signs
and symptoms of disease
Decline phase - subsidence of symptoms.
Recovery phase – symptoms have disappeared,
tissues heal, and the body regains strength.
Phases of Infectious
Disease

53. 
By duration
•Acute – develops and runs its course quickly.
•Chronic – develops more slowly and is usually less severe, but may persist for a
long, indefinite period of time.
•Latent – characterized by periods of no symptoms between outbreaks of illness.

Example of an Infectious Disease -Influenza (Flu)
•Acute contagious disease caused by the influenza virus.
•Respiratory tract infection, but symptoms felt throughout entire body.
•Epidemics occur seasonally with low fatality; more deadly pandemics occur several
times each century.
•Highly changeable virus that can infect multiple species, including humans, pigs,
and birds.
•Concern exists that current avian flu will lead to a new pandemic.
Classification of
Infectious Disease

54. 
•Vaccines
•Antimicrobial drugs
•Good personal hygiene and sanitation
•Protection against mosquitoes
•Quarantine
Measures to reduce the
Spread of Infectious
Diseases

55. 
Emerging diseases are those that have recently appeared within a population, or
whose incidence or geographic range is increasing rapidly.
Diseases can emerge or re-emerge due to:
•Appearance of a previously unknown agent.
•Evolution of a new infectious agent.
•Spread of an infectious agent to a new host.
•Spread of an infectious agent to new locations.
•Acquisition of resistance to anti-microbial drugs.
•Deliberate introduction into a population.
Emerging Infectious
Diseases

56. 
Definitions:
Actions aimed at prevent the occurrence of disease,
eliminating or minimizing the impact of disease and
disability, or if none of these are feasible, retarding
the progress of the disease and disability
Levels of prevention

57. 
•Primordial prevention: Consists of actions and measures that inhibit the
emergence of risk factors in the form of environmental, economic, social, and
behavioral conditions and cultural patterns of living etc.

•Primary prevention: measures for healthy individual to prevent the
occurrence of disease: A. General preventive Measures
B. Specific measures
•Secondary prevention (Control): measures taken after the occurrence of
disease to prevent its spread and complications.
A. Early diagnosis (e.g. screening tests, and case finding)
B- Adequate treatment
•Tertiary prevention: the measures available to reduce or limit impairments
and disabilities, and to promote the patients’ adjustment to irremediable
conditions.”
A- Disability limitation
B- Rehabilitation of handicapped (physical, social, vocational).
Cont,.

58. 
•Successful prevention depends on:
•A knowledge of causation,
•Dynamics of transmission,
•Identification of risk factors and risk groups,
•Availability of prophylactic or early detection and
treatment measures,
•An organization for applying these measures to
appropriate persons or groups, and
Determinants of
Prevention
•Continuous evaluation of and development of procedures
applied

59. 
- General preventive measures through:
•Community development:
•Increase the percapita income.
•Promotion of educational and cultural levels.
•Promotion of health services
•Sanitation of the environment: through
•Town and village planning. - Air sanitation & Good
ventilation.
•Prevention of overcrowding. - Sanitary water
supply.
•Food sanitation - Sanitary waste
disposal
•Insect and rodent control
•Health education:
•This is to educate the public about the prevailing infectious
diseases, mode of transmission and methods of prevention
and control.
•Health promotion: through
•Good nutrition (quantity & quality)
Healthy life-style. - Personal hygiene
•Primary Prevention

60. 
Specific preventive measures: through:
•Immunization:
•Active immunization (vaccines and toxoids)
•Passive immunization (Seroprophylaxis)
•Chemoprophylaxis
Specific protection of individuals by antimicrobial drugs which may be
antibiotics, antimalarial,….etc , given just before exposure or immediately after
exposure to infection.

•- International measures.
Certain regulations to prevent introduction of disease from one country to
another. Include measures: for
•International travelers: valid vaccination certificate is required
•Imported goods - Imported animals
It is mainly directed to Quarantinable diseases i.e. Cholera, yellow fever, plague.

Cont,.

61. 
•Control measures
Definition: measures taken after occurrence of
disease to limit its spread and complications. Control
measures: include
•Control of reservoir: cases, carriers, animals.
•Control of contacts.
•Community Control measures.
•Secondary Prevention

62. 
•Early case finding: by clinical or laboratory
investigation.
•Proper and specific treatment of disease to shorten the
course of the disease.
•Notification to local health authorities (LHA) is necessary
for all infectious disease.
•Isolation of cases: to eliminate the spread of infection to
others, the place of isolation is classified according to
sanitary regulation
•Control of reservoir

63. 
•Recognize the carriers by bacteriologic diagnosis
especially food handlers, teachers, and hospital
workers.
•Examination of contacts
•Trace the source of infection
•Treatment of carriers by chemotherapy.
•Periodic laboratory investigation after release
Health education for the carrier to follow sanitary
habits, disinfection of their discharges.
•Control of carriers:

64. 
•Control of Cattles and sheeps by sanitary
environment,veterinary care, immunization, milk
and meat sanitation.
•Eradication of stray dogs, cats and rodents.
•Quarantine measures for imported animal.
•Protective clothes and precaution for those who are
working with animal.
Control of animal
reservoir:

65. 
•Enlistment: name, age, sex, address, past history of vaccination.
•Investigation of contacts: for case finding or carrier state.
•Specific protection either by immunization or chemoprohylaxis
•Surveillance: contacts observed daily for maximum.
•Segregation where contacts are excluded from work for
maximum to prevent spread of infection to others as food
handles in diphtheria.
•Control of contacts:

66. 
•Isolation of contacts of cholera, pneumonic anthrax
and pneumonic plague .
•Health education and release after becoming
clinically and laboratory free.
Cont,.

67.  When an epidemic or outbreak appears or threatens to occur, preventive and
control measures are needed to protect the at-risk community.

i. Applied Prevention:
•Control of Environment: control of vehicles and vectors according to nature of
disease.
•Health Education of at–risk group or population
•Specific Prevention: mass active immunization or chemoprophylaxis of the at
risk group, if available for encountered disease.
ii. Control Measures:
•Case – finding and control of cases and contacts.
•Epidemiologic investigation, to trace sources and channels of infection.
•Drastic control measures may be taken, if necessary, e.g. closing schools and
public places
•Community Control
Measures

68. 
Than
k You
.