Epidemiology and Diseases Burden of Human Bocavirus 1 Infection in a Children’s Hospital in Japan

Background: Human bocavirus 1 (HBoV1) is a respiratory pathogen predominantly affecting children. However, its epidemiology and clinical impact remain poorly understood. This study aimed to investigate the seasonality, disease burden and clinical features of HBoV1 infection in hospitalized pediatric patients in Japan. Methods: We conducted a retrospective study at Tokyo Metropolitan Children’s Medical Center from September 2023 to August 2024. Children aged ≤15 years hospitalized with respiratory tract infections requiring oxygen therapy and/or noninvasive/invasive mechanical ventilation were included. HBoV1 DNA levels were quantified using real-time polymerase chain reaction (PCR), and acute HBoV1 infection was defined as ≥10 5 copies/mL. A quantitative PCR test was also performed for respiratory viruses simultaneously detected by a multiplex PCR, to distinguish between HBoV1 monoinfection and coinfection with other viruses. Results: Among 327 eligible patients, acute HBoV1 infection was found in 13% (44/327), with peak incidence in June and July 2024. HBoV1 monoinfection was 41% (18/44). The patients with HBoV1 monoinfection had a median age of 25 months (interquartile range, 14–50), and 39% had underlying diseases. Fever and cough were common symptoms, and wheezing was observed in half of the patients. Intensive care unit admission was required in 33% of the patients with HBoV1 monoinfection, with 67% of them requiring mechanical ventilation. HBoV1 was the 3rd most common cause in patients admitted to the intensive care unit (19%). Conclusions: HBoV1 was prevalent in the late spring and early summer during the 2023 to 2024 season in Tokyo, Japan. HBoV1 may contribute substantially to the burden of severe pediatric respiratory tract infections.