1. Epidemiology in Community Health Care
Chapter 7
Epidemiology in Community Health Care

2. Objectives: Upon mastery of this chapter, you should be able to:
Explore the historical roots of epidemiology.
Explain the host, agent, and environment model.
Describe theories of causality in health and illness.
Explain a “web of causation” matrix that assists you with recognition of multicausal factors in disease or injury occurrences.

3. Objectives:
Define immunity and compare passive immunity, active immunity, cross-immunity, and herd immunity.
Explain how epidemiologists determine populations at risk.
Identify the four stages of a disease or health condition.
List the major sources of epidemiologic information.

4. Introduction
In this unit, the focus is on epidemiology, communicable disease control, and environmental health and safety. These are cornerstone areas of public health practice and are just as important at the local level as at the regional, national, and international levels.

5. Definition of health
The World Health Organization (WHO) defines the health as “ a state of complete well-being, physical, social, and mental, and not the absence of diseases …. 1988

6. Definition of Epidemiology
Epidemiology :is the study of distribution and determine of health-related states or events in specific populations, and the application of this study to control of health problems

7. What is Epidemiology? Science of Public Health that studies:
Distribution of disease
Determinants of health/disease
Specific populations
Look for patterns of disease
Time, place, personal characteristics
Interventions
Prevention is key

8. What does Epidemiology study?
Health-related
Infectious disease
Chronic disease

9. Historical Roots of Epidemiology
Ancient Times:
Hippocrates, Greek physician 460 to 375 BC
Middle Ages:
1348: Plague (Black Death)
18th century:
Florence Nightingale (1820–1910)
19th century: modern epidemiology
sanitary statistics
infectious-disease epidemiology
chronic-disease epidemiology

10. Epidemiologic Information
1) Case definition
2) Person
3) Place
4) Time

11. 1) Case Definition
Standard set of criteria
Clinical and lab
Allows for comparison

12. Case Definition example :
Smallpox
Clinical Description
An illness with acute onset of fever >101 °F followed by a rash characterized by vesicles or firm pustules in the same stage of development without other apparent cause.
Laboratory Criteria for Confirmation
Isolation of smallpox (variola) virus from a clinical specimen, or

13. Case Definition Gradient
High Specificity
Low Specificity
Suspected
Probable
Confirmed

14. 2) Person
Age
Sex
Race/Ethnicity
Socio-Economic Status
Behaviors

15. 3) Place Geographic Distribution Natural Clustering vs. uniform Home
Work
School
Hospital room

16. Regional HIV and AIDS statistics and features, 2006
TOTAL
North America
Eastern Europe & Central Asia
Latin America
South and South-East Asia
Sub-Saharan Africa
Oceania
Western & Central Europe
Caribbean
East Asia
Middle East & North Africa
18 000
[ – ]
84 000
[ – ]
65 000
[ – ]
[ – ]
2.1 million
[1.8 – 2.4 million]
[ – ]
2.9 million [2.5 – 3.5 million]
0.8%
[0.6% – 1.1%]
0.9%
[0.6% – 1.4%]
0.5%
[0.4% – 1.2%]
0.6%
[0.4% – 1.0%]
5.9%
[5.2% – 6.7%]
1.0%
[0.9% - 1.2%]
4.3 million [3.6 – 6.6 million]
43 000
[ – ]
[ – ]
[ – 2.3 million]
2.8 million
[2.4 – 3.2 million]
4000
[2300 – 6600]
12 000
[ <15 000]
19 000
[ – ]
[ – ]
36 000
[ – ]
0.4%
[0.2% – 0.9%]
0.3%
[0.2% – 0.4%]
1.2%
[0.9% – 1.7%]
0.1%
[<0.2%]
0.2%
[0.1% – 0.3%]
7100
[ 3400 – ]
22 000
[ – ]
27 000
[ – ]
[ – ]
68 000
[ – ]
Adult & child
deaths due to AIDS
Adult (15‒49) prevalence [%]
Adults & children newly infected with HIV
Adults & children living with HIV
24.7 million
[21.8 – 27.7 million]
39.5 million [34.1 – 47.1 million]
1.4 million
[ – 2.2 million]
1.7 million
[1.2 – 2.6 million]
[1.3 – 2.5 million]
7.8 million
[5.2 – 12.0 million]
81 000
[ – ]
[ – ]
[ – ]
[ – 1.2 million]
[ – ]
Regional HIV and AIDS statistics and features, 2006
Table b

17. Geographic Distribution

18. 4) Time Onset of symptoms Incubation Period Infectious Period
Seasonality
Baseline vs. epidemic
Interval
Long-term trends
Shorter for environmental exposure

19. Mortality versus Morbidity rate
Mortality rate : is a measure of the number of deaths (in general, or due to a specific cause) in some population, scaled to the size of that population, per unit time.
* Morbidity rate : refers to the number of individuals who have contracted a disease during a given time period

20. Examples : *Mortality rate :
Ex. Number of deaths from TB is 39 per population in KSA.
*Morbidity rate :
Ex.: the number of HIV cases is 432 per population in South Africa.

21. Epidemiologic Triangular: Host, Agent, & Environment
susceptible human or animal who harbors and nourishes a disease-causing agent
2)Agent
a factor that causes or contributes to a health problem or condition
3)Environment
all the external factors surrounding the host that might influence vulnerability or resistance

22. Epidemiologic Triangular

23. Epidemiologic Triangular

24. Theories of Causality in Health and Illness
Relationship between a cause and its effect
1) Chain of Causation:

25. Chain of Infection

26. Web of Causation: Infant Mortality
2) Multiple Causation:

27. Transmission b) Indirect a) Direct Portal of Entry Portal of Exit
Airborne
Vehicle
Vector
Mechanical vs. biologic
a) Direct
Contact
Droplet
Portal of Entry
Portal of Exit

28. Definition & Types of Immunity
A host’s ability to resist a particular infectious disease–causing agent.
Acquired immunity: is the resistance acquired by a host as a result of previous natural exposure to infectious agent
Ex. : having a measles once protects against future infection
* Acquired immunity may be induced by active or passive immunity

29. Types of immunization :
1- Active immunity:
refers to immunization of an individual by administration of an antigen (infectious agent or vaccine ) and usually characterized by the presence of an antibody produced by the individual host
*long-term immunization
Ex.: vaccination of the children against measles .

30. Types of immunization :
2- Passive immunity:
refers to immunization through the transfer of specific antibody from an immunized individual to no immunized individual .
* short-term immunization.
Ex .: used of immunoglobulin to hepatitis patient .

31. Populations at Risk
The risk of developing a health problem is directly influenced by their biology, environment, lifestyle, and system of health care.

32. Four Stages of a Disease or Health Condition

33. Major Sources of Epidemiologic Information
Existing Data
Vital Statistics
Census Data
Reportable Diseases
Disease Registries
Environmental Monitoring
Informal Observational Studies
Scientific Studies

34. Incidence rate Incidence rate:
Number of new disease cases per population at risk
High incidence implies high disease occurrence
Low incidence implies low disease occurrence
Measured over a given time interval
Usage:
1-Determine probability of developing a specific disease
2-Used to detect etiologic factors
refers to all new cases of a disease or health condition appearing during a given time.

35. Incidence rate formula :
Ex.: the number of people age at risk at 10,000, since all the time new people are entering the population at risk ( 100 cases )
Number of persons developing a disease x100% Total number

36. Summary Case definition, person, time, place Know disease/agent
Triangular epidemiology
Passive and active immunization
Incidence rate calculation