The public health community can trace its roots to fourteenth-century Italy, when fear of the Black Death prompted the government of Venice to exclude from their ports those ships with persons reported to have pneumonic plague. More recent epidemics of acquired immunodeficiency syndrome, vaccine-preventable diseases, and drug-resistant conditions pose imminent threats. The public health approach to such problems is fourfold: (1) define the problem; (2) identify risk factors; (3) develop and test prevention strategies; and (4) implement prevention programmes. Disease eradication, the ultimate disease control measure, is simple in concept (focusing on a single unequivocal outcome), but extraordinarily difficult in implementation.

Public health uses the sciences of geography and statistics, as well as epidemiology, the laboratory, and the behavioural and social sciences, to detect health problems in communities of people and to intervene and prevent further illness, disability, and premature death. Variations in the usual incidence of health events in different geographical areas or in different time periods may provide important clues to the aetiology of the disease or to specific risk factors for the event. A foundation of the science of epidemiology is a study of the departure of observed disease experience from the expected occurrence.

Public health surveillance provides much of the data needed for modern public health. The term surveillance is derived from the French word meaning ‘to watch over’ and, as applied to public health, means the close monitoring of the occurrence of selected health events in the population.