In Reply: Acute Human Bocavirus 1 Infection in Children Hospitalized for Acute Bronchiolitis: A 2-year Prospective Study

To the Editors: Human bocavirus 1 (HBoV1) is frequently detected in pediatric respiratory infections; however, its role as a causative pathogen remains uncertain. Uršič et al. in their study “Acute Human Bocavirus 1 Infection in Children Hospitalized for Acute Bronchiolitis; A 2-Year Prospective Study,” investigates HBoV1’s role in bronchiolitis by distinguishing active infection from mere viral presence through mRNA detection.1 While the study provides valuable insight, several methodological limitations affect its ability to establish HBoV1 as a true causative agent. One significant limitation, acknowledged by the authors, is the small number of HBoV1 mRNA-positive cases (n = 9), which restricts statistical power and the ability to draw definitive conclusions about the virus’s role in active infection. Additionally, a significant limitation of the study is the age disparity between the bronchiolitis and control groups, with the control group (mean age: 30.4 months) being significantly older than the bronchiolitis group (mean age: 12.6 months). Since HBoV1 is most commonly detected in children under 24 months,2 the lower prevalence in the older control group may be due to preexisting immunity or viral clearance, making comparisons less meaningful. A younger, age-matched control group would have improved the study’s reliability. Sex imbalance is another confounding factor, as male infants are more susceptible to severe respiratory infections.3 The bronchiolitis group had 68.8% males, which may have increased HBoV1 detection simply due to their higher likelihood of hospitalization, rather than indicating a causal relationship. Without proper adjustments, the study cannot confidently conclude that HBoV1 is a primary driver of bronchiolitis rather than an incidental finding. Furthermore, the persistence of HBoV1 DNA for weeks after infection raises concerns about misclassification bias, as a positive DNA test does not necessarily indicate an active infection. Some cases labeled as “acute HBoV1 infection” may instead reflect viral persistence from a prior exposure. The absence of serological testing, such as IgM/IgG antibodies, further weakens the ability to differentiate acute from past infections. Additionally, the study relies solely on nasopharyngeal swabs rather than lower respiratory tract samples, limiting its ability to confirm whether HBoV1 was actively causing lower respiratory tract disease or was merely present in the upper airway. Nasopharyngeal swabs collect limited material, which may have led to missed infections and inaccurate detection rates. Another significant limitation is the lack of longitudinal follow-up, which prevents an assessment of whether HBoV1-positive children experienced prolonged symptoms, increased hospital readmissions, or a higher risk of developing chronic respiratory conditions like wheezing or asthma. Without tracking patients beyond hospitalization, the study can only establish the presence of HBoV1 in some bronchiolitis cases, but cannot determine its long-term clinical significance.4 In conclusion, this study provides valuable insight into HBoV1’s potential role in bronchiolitis. However, its methodological limitations hinder definitive conclusions. Future research should address these gaps by incorporating larger, age-matched cohorts, serological testing, lower respiratory tract sampling, and longitudinal follow-up to better establish the clinical impact of HBoV1 in bronchiolitis.