Hepatitis A outbreaks in China during 2006: application of molecular epidemiology

In China, hepatitis is a huge public health problem. Outbreaks of hepatitis A are the most frequent cause of acute hepatitis, and to date, few epidemiologic investigations or molecular surveillance studies have been performed. In 2006, two major outbreaks of hepatitis A occurred, one in Guigang City, southern China, and the other in Hetian City, northwestern China. Field and molecular epidemiologic investigations were conducted. In Guigang, a single outbreak occurred in a school; 35 patients and 25 asymptomatic individuals were infected with 1 strain of hepatitis A virus (HAV). A case-control study showed that contaminated water was the likely transmission source. In Hetian, the epidemic of hepatitis A consisted of sporadic, small outbreaks involving as many as 20 wild HAV strains. A molecular epidemiology approach allowed us to identify two groups infected by individual HAV strains. Further fieldwork and a case-control study showed that ice cream was the suspected transmission source in one group. Our molecular epidemiology study showed that genetic variability between the HAV strains isolated from Guigang and Hetian and previously reported HAV strains was at least 4.3%. Contaminated water and suspected ice cream were associated with outbreaks of hepatitis A. Viral genetic analysis may advance field investigations in complex situations.