Abstract

Three consecutive outbreaks of Salmonella enteritidis PT4 occurred in Wales in 1989 in which epidemiological and microbiological investigation established eggs as the likely source although kitchen inspection and food preparation histories suggested other vehicles of infection. This paper examines the contribution of analytical epidemiology in attributing causation, with particular reference to those limitations which are regarded as inherent in epidemiological evidence. Such evidence, implicating eggs in the three outbreaks, fulfilled 6/7 widely accepted criteria for causation; data to assess the seventh were lacking. Collaboration between different agencies and professionals in investigating outbreaks is very important.