[Risk factors analysis of epidemic hepatitis A in a factory in Shanghai]

An investigation of the epidemic of hepatitis A which occurred in early 1988 in Shanghai was conducted at the Shanghai Number 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 and workers who ate raw clams (18%) but also 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 = 3.0, 95% confidence interval: 2.0, 4.5) shift work (relative risk = 3.3, 95% confidence interval: 1.9, 5.8) and eating out (relative risk = 4.7, 95% confidence interval: 2.3, 9.7). The consumption of clams contaminated with hepatitis A virus was the main risk factor in this episode. The study indicates that strengthening surveillance of shellfish hygiene is important to prevent future epidemics of hepatitis A.