Etiological diagnosis and genotyping analysis of an outbreak of hepatitis A

Objective　The study was conducted to identify the pathogens causing a local outbreak of hepatitis A in Ningbo in 2004 and analyze its gene characteristics. Methods　HAV IgM and HEV IgM of serum samples were detected by using ELISA test; HAV RNA in stool samples was detected by RT PCR; VP1 gene of HAV was cloned by RT PCR and sequenced; the sequence results were analysed by DNAstar. Results　All 172 serum samples were positive for HAV IgM and negative for HEV IgM, and HAV RNA was detected from 74 stool samples, accounting for 43.0%. The HAV VP1 genes of five samples were cloned and sequenced, the results of which suggested that the VP1 genes of 4 strains (NB2004-10, NB2004-11, NB2004-51 and NB2004-71) were identical, and the nucleotide homology between NB2004-75 and these 4 strains was 99.9%, and the amino acid homology was 99.7%. Comparing with various genotypes of HAV, Ningbo strains had the highest homology to AH2 nucleotide and amino acids of subtype IA strains, (98.9% and 99.7%-100.0%, respectively). Compared with other prevailing strains in China, its homology of nucleotide and amino acid ranged from 89.4% to 96.7% and from 97.0% to 100.0%, respectively. Conclusion　The pathogen that caused this outbreak was hepatitis A virus; the genotype of the strains was serotype IA, which had the closest homology to Japanese strains AH2 and AH3 but was of a different evolutional branch from other prevailing strains in China.