Background: As a result of declining hepatitis A endemicity in Thailand, an increasing number of children and adolescents have become susceptible to hepatitis A virus (HAV) infection.
Objective: The present study was aimed at both investigating the clinical features and determining molecular characterization of HAV during an outbreak, which occurred in a childcare center located in a suburban area of Bangkok between November 2002 and February 2003.
Methods: Serum samples obtained from all children in the center were tested for anti-HAV IgG and anti-HAV IgM. Testing for HAV-RNA was performed in sera, saliva and stool samples by the reverse transcription-polymerase chain reaction (RT-PCR) with primers located at the VP1-2A region. To further characterize the HAV genotype serum derived HAV-RNA-positive PCR products were sequenced.
Results: Anti-HAV IgG and anti-HAV IgM were detected in 74 and 70 of 112 children in the center, respectively. Among those positive for anti-HAV IgM, 65 cases were asymptomatic, while five children had acute clinical hepatitis. The ratio between symptomatic and asymptomatic children was 1:13. Among the asymptomatic cases, 31 (47.7%) displayed biochemical hepatitis with elevated alanine aminotransferase (ALT) levels. All the isolates from this outbreak were found to be of subgenotype IA, which showed a high level of sequence homology with previous Thai isolates. HAV-RNA could not be detected in saliva, but was found in stool for at least 3 weeks after initial diagnosis of clinical or biochemical hepatitis.
Conclusion: Because of the infection's characteristically asymptomatic spread, hepatitis A poses an increased risk to childcare centers. The presence of a single sub-genotype indicates that this HAV strain has been predominantly circulating in Thailand.