The frequency of HBoV codetection with other respiratory viruses was 18.3% in the HBoV-positive samples and was lower than the previously published data [4, 20] . This difference in the codetection frequency is attributed to the different detection methods; molecular diagnostic methods were used for the detection of other respiratory viruses in the other studies whereas we used virus culturing. Among the 17 HBoV-positive patients who were also positive for infection with other viruses, 10 showed PIV infection. The high association of HBoV with PIV seems to be attributed to the high prevalence of PIV infection in 2006 (22.8% in May). Interestingly, almost all cases (except two) positive for both HBoV and another respiratory virus belonged to the low-viral-load group. As the virus culture was used for the detection of major respiratory viruses, the isolated virus could be the main causative agent of respiratory illness. Therefore, the presence of low copy number of HBoV, detected by molecular method, may indicate prolonged viral shedding or an asymptomatic infection. Recently, prolonged presence of HBoV in NPAs has been reported [21] . These results suggest that single HBoV infection in the high-viral-load group may play an active role in respiratory infection. These findings are consistent with a Norwegian study that reported detection of HBoV alone and a high-vi- Low-viral-load High-viral-load KJLM ral-load were associated with respiratory tract infection [20] . In that study, patients with a high-viral-load in NPAs developed viremia more frequently than the patients with a moderate-or a low-viral-load did. In our study, HBoV-positive patients in the high-viral-load group showed significantly higher pulse rates and respiratory rates than the in the low-viral-load group. These findings also support the idea that a high-viral-load may be associated with a respiratory infection.