Wang JY (Division of Gastroenterology, Zhong Shan Hospital, Shanghai Medical University, China), Hu SL, Liu HY, Hong YL, Cao SZ and Wu LF. Risk factor analysis of an epidemic of Hepatitis A in a factory in Shanghai. International Journal of Epidemiology 1990, 19: 435–438. Investigation of an epidemic of hepatitis A which occurred in Shanghai in early 1988 was conducted at the Shanghai No. 2 Yarn Dyeing and Weaving Mill. In this factory the attack rate between January and April 1988 was 9%. The rate was highest among staff who ate raw clams (18%) and higher among those who ate cooked clams (7%) than among those who did not eat clams (2%). In addition, independent risk factors for infection were: age below 30 years (relative risk (RR)=3.0, 95% Cl: 2.0, 4.5) shift work (RR=3.3, 95% CI: 1.9, 5.8) and eating out (RR=4.7, 95% CI: 2.3, 9.7). Consumption of clams contaminated with hepatitis A was the main risk factor in this episode. The study indicates that strengthening surveillance of shellfish hygiene is important in preventing future epidemics of hepatitis A.