Our age stratification data indicates that HBoVs circulate widely in the human population, and the primary infection with HBoV1-3 occurs in children aged six months and older after the maternal antibodies have waned. The seropositive rates of IgG antibodies against HBoV2, 3 and 4 were lower than that of HBoV1 in individuals of $0.5 years old. These data indicate that HBoV1 is the predominant circulating species of HBoV in Beijing, whereas HBoV2-4 do not seem to have a major impact on HBoV infections. This finding agrees with reports on HBoVs prevalence obtained from most parts of the world using DNA analysis [10, 14, 16] . Of note, our finding that the seroprevalence of HBoV4 is much lower than that of HBoV1-3 is consistent with the rare detection of HBoV4 DNA in clinical samples [9] . Overall, the seroprevalence of HBoVs indicated by results of the cELISA decreased less in children than in adults in comparison to the results without competition, indicating that HBoV infections are more specific in children, especially for HBoV1 [22] . These results suggest that HBoV species may play differential roles in disease.