Inapparent infection of hepatitis A virus.

To detect inapparent infection with hepatitis A virus, serial sera were collected from patients with hepatitis A and their contacts in two waterborne epidemics in China. Epidemic 1 occurred in a rural village near Hangzhou during August 1978-January 1979, and epidemic 2 took place in a rural primary school in Pinghu County in Zhejiang in April-May 1985. These sera were tested for antibodies against hepatitis A virus (anti-HAV), serum glutamic pyruvic transaminase (SGPT) activity, and icteric index. Feces also were collected in epidemic 1 to test for hepatitis A virus antigen. Both anti-HAV immunoglobulin M (IgM) and total anti-HAV were assayed in sera from "healthy persons" (symptomless persons without icterus and with normal SGPT level) who were in close contact with hepatitis A patients. In epidemic 1, among 18 "healthy persons", 12 were anti-HAV IgM positive, two were immune, and four susceptibles escaped infection. In epidemic 2, among 32 "healthy children", three were anti-HAV IgM positive, five had been infected by hepatitis A virus in the past, and 24 were not infected. These results demonstrate that inapparent infections occur along with overt and subclinical infections during epidemics of hepatitis A. The proportions of inapparent, subclinical, and overt infections were, respectively, 34.3%, 45.7%, and 20% in epidemic 1, and 25%, 50%, and 25% in epidemic 2. In addition, hepatitis A virus particles were demonstrated in the feces of all infected subjects who were examined and who included all levels of clinical response. These particles were identified with immuno-electron microscopy and enzyme-linked immunoassay.