Epidemiology

EPIDEMIOLOGY Study of occurrences and distribution of

diseases as well as the distribution and determinants of health states or events in specified population, and the application of this study to the control of health problems.

Areas of Investigation: 1. Study of the distribution of disease 2. Search for determinants of the disease and

its observed distributions.

Uses of Epidemiology Study the history of the health population and

the rise and fall of diseases and changes in their character. Diagnose the health of the community and the condition of people Study the work of health services with a view of improving them.

Estimate the risk of disease, accident, defects

and the chances of avoiding them. Identify syndromes by describing the distribution and association of clinical phenomena in the population

Complete the clinical picture of chronic

disease and describe their natural history Search for causes of health and disease

EPIDEMIOLOGIC TRIANGLE HOST

AGENT

ENVIRONMENT

Host Any organism that harbors and provides

nourishment for another organism

Agent the infectious agent or the toxic component

that is transmitted from the source of infection to the susceptible body

Environment The sum total of all external condition and

influences that affects the development of an organism Components Physical Environment  Biological environment  Socio-economic 

Classification of Agents: A. Nutritive Elements A. Excess B. Deficiencies B. Chemical Agents A. Poisons B. Allergens C. Physical Agents

D. Infectious Agents Metazoa Protozoa Bacteria Fungi Ricketssia Viruses

Classification of Host Factors (Intrinsic Factors) A. B. C. D. E. F.

Genetic Age Sex Ethnic Group Physiologic Immunologic Experiences Passive B. Active A.

G. Inter-current or pre-existing disease H. Human behavior

Environmental Factors (Extrinsic Factors) A. Physical environment B. Biologic Environment A. Human population B. Flora C. Socio-Economic environment A. Occupation B. Urbanization C. Disruption

EPIDEMIOLOGY VARIABLES Time Person Place

Time Refers to the period during which the cases of the disease being studied were exposed to the source of infection Period during which the illness occured Cases are grouped according to: Epidemic Period: a period during which the reported number of cases of the disease exceed the expected

Year 

Take into consideration seasonal variations

Period of Consecutive years 

Useful in prediction the probable future incidence of the disease and in planning appropriate prevnetion and control programs.

Persons Refers to the characteristics of the individual

who were exposed and who contacted the infection or the disease in question Described according to: Acquired characteristics Activities Circumstance which they live

Age Considered the single most useful variable

associated in describing the occurrence and distribution of a disease Potential for exposure to a source of infection  Level of immunity or resistance  Physiologic activity at the tissue level 

Sex and occupation In general, males experience higher mortality rates than female for a wide range of diseases Females have higher morbidity causes

Place Refers to features, factor or conditions which

existed in or described the environment in which the disease occured. Described according to street, address, city, municipality, province, region, or county

Urban/rural differences: In general, disease spreads more rapidly in urban areas than in rural areas Socio-economic areas Different communities can be usually divided into geographic areas which are relatively homogenous with respect to the socioeconomic circumstances of the residents

Patternf of Occurrence and Distribution Sporadic The intermittent occurrence of a fewisolated and unrelated cases in a given locality No apparent relationship between cases Endemic occurrences Is the continuous occurrence troughout a period of time, of the usual number of cases in a given locality

Disease in inherent in that locality  Identifiable with the locality itself 

Epidemic Of unusually large number of cases in a

relatively short period of time. Number of cases is much more than the usual numer in that locality

Pandemic Simultaneous occurrence of epidemic of te

same disease in several countires. International in perspective

Most interesting and most meaningful Demands immediate effective action Factors Contributory to Epidemic

Occurrence Agent Factor Host factors Environmental factors