Hepatitis A in New South Wales, Australia, from consumption of oysters: the first reported outbreak

Between 22 January and 4 April 1997, 467 hepatitis A cases were reported to the New South Wales Health Department, Australia. To identify the cause of the outbreak, we conducted a matched case-control study, and an environmen tal investigation. Among 66 cases and 66 postcode-matched controls, there w as a strong association between illness and consumption of oysters (adjuste d odds ratio 42; 95% confidence interval 5-379). More than two-thirds of ca ses reported eating oysters, including one third of cases and no controls w ho reported eating oysters in the Wallis Lake area. A public warning was is sued on 14 February, and Wallis Lake oysters were withdrawn from sale. Hepa titis A virus was subsequently identified in oyster samples taken from the lake. Hepatitis A virus poses a special risk to consumers who eat raw oyste rs because it can survive for long periods in estuaries and cause severe di sease.