Epidemiology is the study of the distribution and determinants of health-related states or events (including disease), and the application of this study to the control of diseases and other health problems. Various methods can be used to carry out epidemiological investigations: surveillance and descriptive studies can be used to study distribution; analytical studies are used to study determinants.

It is the cornerstone of public health, and shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare.


Basic principles of epidemiology in emergencies

Epidemiology is the study of the causes and distribution of disease in human populations. An epidemiological approach helps planners to focus on the main problems of a community rather than of individual patients and to identify measures for improving the health of the community as a whole.
Epidemiology can increase the general understanding about a disease and particularly how it is transmitted even when the cause is unknown.

 In epidemiology, the assumption is that diseases do not occur randomly, but follow predictable patterns that can be studied and expressed in terms of what, who, where, when, how, why, and what next.



In emergencies, epidemiology has three elements:

1. Descriptive Epidemiology determines the distribution of a disease among displaced populations. It describes the health problem, its frequency, those affected, where, and when. The events of interest are defined in terms of the time period, the place and the population at risk.

Examples: Monitoring the health status of a population to detect cholera cases, such as, by age, sex, location, water source and duration of stay in a dispersed population or camps.
Conducting a nutritional survey to determine the prevalence of acute malnutrition among children under five.

2. Analytical epidemiology compares those who are ill with those who are not in order to identify the risk of disease or protective factors (determinant of a disease). It examines how the event (illness, death, malnutrition, injury) is caused (e.g. environmental and behavioural factors) and why it is continuing. Standard mathematical and statistical procedures are used.

Example: Investigating an outbreak of an unknown disease in a displaced
population settlement.

3. Evaluation epidemiology examines the relevance, effectiveness and impact of different programme activities in relation to the health of the affected populations.

Example: Evaluating a malaria control programme for displaced populations.


Key aspects of epidemiology

A number of other fields – medicine, nursing, dentistry, pharmacy, demography, sociology, health psychology, health education, health policy, nutrition – share many common features and areas of
interest with epidemiology (and with each other).

Some of the key aspects of epidemiology are:
Epidemiology deals with populations, thus involving:
1. Rates and proportions
2. Averages
3. Heterogeneity within
4. Dynamics – demography, environment, lifestyle



Epidemiology has many uses in emergency situations, including:
ƒ 1. Rapid needs assessment;
ƒ2. Demographic studies determining the population size and structure of affected communities in camp settings or dispersed within a host population;
ƒ 3. Population surveys for determining health status (death rates, incidence/prevalence of disease, nutrition and immunisation status) and assessing programme coverage;
ƒ 4. Investigating a disease outbreak;
ƒ 5. Public health surveillance and management information system;
6.ƒ Programme monitoring and evaluation.



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