Seroprevalence and genotype distribution of hepatitis A virus in the pre-vaccine era in South Transdanubia, Hungary (2010-2020).

In this study, the age-related seroprevalence of hepatitis A virus (HAV) infection was investigated in the population in South-Transdanubia, Southwest Hungary (Central Europe) between years 2010 and 2020. Up to the age of 40, the HAV seropositivity was less than 18% in all age groups indicating a low level of HAV endemicity in this part of the country in the covered study period. The HAV seropositivity started to increase at the age group 41-45 years, reaching the ∼50% at age group 56-60, and 75-80% at age group 66-70, respectively. A total of 43 (0.2%) of the 21,106 tested sera were HAV IgM-positive (the annual percentage range of HAV IgM-positivity was 0.046-0.6%). Total of 24 (55.8%) of the 43 HAV IgM-positive samples tested RT-PCR-positive confirmed as HAV sub-genotypes IA (N = 17; 70.8%) and IB (N = 7; 29.2%), respectively. Imported HAV infections (three cases from Romania, and one-one case from Austria and Italy), two small outbreaks and 11 cases of a genetically identical sub-genotype IA strain (GenBank number of the prototype strain: KM657825) from 2012 to 2014 were identified later connected directly to the enormous HAV outbreak initiated among men who have sex with men (MSM) at the end of 2011 in the capital Budapest. In summary, low endemicity but high and increased susceptibility for HAV infection was found in the population in Southwest Hungary, where repeated introduction of sub-genotypes IA and IB HAV strains were identified between 2010 and 2020.