Persistence of a positive test for IgM antibodies to hepatitis A virus in late convalescent sera.

We had the opportunity to carry out a long-term follow up of 15 patients with viral hepatitis Type A. The serum IgM response to hepatitis A virus (HAV) was investigated with a commercially available kit (HAVAB-M). IgM antibodies were detected in all specimens collected during the acute phase of the disease and during early convalescence (first 3 months). However, there was a clear decrease in the "sample-to-cutoff" ratio (s/co ratio) after the first 2 months. Serum samples were available from six patients 30 to 32 months after onset of illness. Two of these were positive for IgM anti-HAV, but the s/co ratios were low. These results point to the need for careful evaluation of the diagnosis of acute or recent viral hepatitis Type A when low s/co ratios are obtained.