Serologic Diagnosis of Human Bocavirus Infection in Children

Abstract

To the Editors: Blessing et al published recently in the journal their interesting findings on prolonged human bocavirus (hBoV) DNA shedding by repeated nasopharyngeal aspirates (NPA) in 6 children.1 The interval between the samples varied from 29 to 142 days. In the latter case, the prolonged shedding was documented by 6 samples taken on days 0, 25, 53, 78, 135, and 142.1 The authors concluded that, in contrast to most other respiratory viruses, hBoV DNA detection in a single NPA sample is not sufficient to implicate hBoV as the causative agent of acute respiratory tract disease. The authors proposed that serologic assays, detection of hBoV viremia or high viral loads in NPA samples may be more useful approaches. We have recently introduced new IgM and IgG enzyme immunoassays (EIAs) for the diagnosis of acute respiratory tract hBoV infection.2 In 48 wheezing children with hBoV infection diagnosed by EIA in paired sera, 45 (94%) had viremia and 35 (73%) had hBoV in NPA by polymerase chain reaction (PCR). The EIA test was diagnostic in 27/28 (96%) of those with a high load hBoV DNA in NPA, and in 45/49 (92%) of those with hBoV DNA in serum. The respective figure in those with a low load of hBoV in NPA was 38%. About 12 children had a single hBoV infection, though an extensive test panel, including PCR, culture, antigen detection, and antibody assays, was in use for other viruses.2 In 101 children with pneumonia, serologic evidence of acute hBoV infection was found in 12 (12%) by EIA.3 Significant increases in IgG antibodies were seen in 7 cases, IgM antibodies were seen in 11 cases, and both IgG and IgM findings were documented in 6 cases. In IgG positive cases, the increases in IgG antibodies between paired sera varied from 9- to >100-fold. Thus, our findings by antibody assays verify the notion of Blessing et al, as well as other recent findings4 that hBoV is a true pathogen in respiratory tract infections in children. Qualitative PCR in NPA alone is not sufficient for a reliable hBoV diagnosis. Our results highlight the role of antibody assays. Matti Korppi, MD, PhD Pediatric Research Center University Hospital, Tampere University Tampere, Finland Tuomas Jartti, MD, PhD Department of Pediatrics University Central Hospital Turku University Turku, Finland Klaus Hedman, MD, PhD Department of Virology Maria Söderlund-Venermo, PhD Department of Virology Helsinki University Central Hospital Laboratory Division Helsinki, Finland