SEVERE DISEASE ASSOCIATED WITH ACUTE HUMAN BOCAVIRUS INFECTION

Background: Human bocavirus (HBoV) was first described in 2005 and has primarily been found in children with respiratory tract disease. Studies applying PCR to respiratory tract samples have frequently found HBoV in association with other viruses, and its causative role for disease has therefore been questioned. We have reported that only a fraction of patients with detectable HBoV in the respiratory tract have serological evidence of acute HBoV infection, and that those patients frequently also have a high viral load in the respiratory tract and detectable HBoV DNA in the serum (Kantola et al. CID 2008, Allander et al. CID 2007). This implies that there is prolonged shedding of HBoV in the respiratory tract and that alternative diagnostic methods must be applied for adequate studies of disease association.

Methods: We have routinely offered HBoV diagnostics to clinicians in Stockholm since October 2007 as part of a PCR diagnostic package for 15 respiratory viruses. Cases with a low HBoV load in the respiratory tract are reported as likely of no clinical significance. A serum sample for HBoV PCR is requested from patients with a high viral load.

Results: 13 (4.3%) of 300 samples have been positive for HBoV. Four samples had a viral load higher than10⁵ copies/ml, and serum samples were obtained in two of those cases. In both cases the acute serum samples were positive for HBoV DNA and the convalescent serum samples were negative for HBoV DNA. Serology results were consistent with acute HBoV infection. HBoV was the only microorganism detected. Both patients had a clinical picture compatible with an acute viral respiratory infection. Patient one was an 11-year old boy with leukaemia and pancytopenia who was hospitalized for 4 days with high fever, sore throat, cough and rhinorrhea. Patient two was a 4-year old girl with a history of recurrent infection-associated wheezing, who suffered a life-threatening febrile acute wheezing episode that required extracorporeal membrane oxygenation treatment.

Conclusions: Acute HBoV infection can be diagnosed by serology and detection of HBoV DNA in serum. By this diagnostic strategy we identified few but surprisingly severe cases with implied HBoV etiology. Future studies of HBoV and disease will have to apply strict diagnostic methods to identify only cases with acute infection.