Epidemiology in search of infectious diseases: methods in outbreak investigation.

The value of epidemiology in the investigation of incidents of infectious disease in the UK does not seem to be always readily appreciated within microbiology' 2 or environmental health.3 Yet because microbial disease is a result of the interaction of the agent, the host and environmental factors4 neither laboratory diagnosis nor environmental inspection are of themselves sufficient for successful investigation and control. Simply isolating microbes from the environment, even ifappropriate samples are available, cannot distinguish between a reservoir ofan agent and the outbreak source or cross contamination from the reservoir or source. Microbiologically plausible explanations of outbreaks may be wrong, but it is often difficult to persuade investigators of the need to test such hypotheses. On the other hand, whilst epidemiology may have evolved from the study ofinfectious disease epidemics, academic epidemiology seems in the main to have passed infectious diseases by in the UK. This is regrettable as there is still the need to consolidate the foundations of a section of public health medicine which has refused to disappear.5 This review, in following the steps taken in an outbreak investigation,6 draws attention to both the usefulness of epidemiology and to regularly recurring methodological problems which may be encountered.