Acute-phase (at the time of admission) and convalescent-phase (2 weeks later) serum samples and NPA samples at the time of admission were obtained from 259 children (age range 3 months to 15 years, median 1.6 years) with acute expiratory wheezing (10, 16) . These children were tested by NPA PCR for 16 respiratory viruses (10) ; 117 of these children were tested by HBoV IgM and IgG immunoblots and HBoV serum qPCR (10, 11) . All remaining serum samples, except 1 convalescent-phase serum sample that Clinical Assessment and Improved Diagnosis of Bocavirus-induced Wheezing in Children, Finland was depleted, were tested by HBoV qPCR specific for the nucleoprotein 1 gene as described (11) ; all serum samples were tested by EIA. For 93 of these 258 children, follow-up serum samples were obtained 5-8 years later. In addition, 115 serum samples from healthy medical students were collected after informed consent was obtained. The study was reviewed and approved by the Ethics Committees of Turku and Helsinki University hospitals.