Human bocavirus (HBoV) is a new parvovirus that was first identified in 2005 in Sweden.1 Soon after its discovery, HBoV was detected globally in respiratory tract samples and in a maximum of 19% of hospitalized children with acute wheezing.2 In wheezing children, the detection of high copy number of HBoV DNA in a respiratory specimen, HBoV DNA in serum, HBoV IgM antibodies, or HBoV IgG seroconversion has been suggested as the most definitive indication of HBoV infection.2,3
Systemic corticosteroids are a cornerstone of the management of moderate-to-severe episodes of recurrent wheezing and acute asthma. However, among young wheezing children, it is difficult to determine who will benefit from systemic corticosteroids. It seems that those affected by respiratory syncytial virus (RSV) do not benefit,4–6 but those affected by rhinovirus may benefit.7–9 To date, there are no studies on the efficacy of systemic corticosteroids in wheezing children with HBoV infection. We hypothesized that prednisolone is effective in acute wheezing associated with HBoV infection.
We used the data from a previous VINKU study, which included children hospitalized for acute wheezing.7–9 The study was carried out in the Department of Pediatrics of Turku University Hospital between September 2000 and May 2002 (excluding 6–7/2001 and last week of 2001). The original aim of the study was to evaluate the efficacy of systemic corticosteroid therapy in relation to viral etiology of the illness.7–9 To this analysis, we included all children ≤6 years of age with complete HBoV diagnostics performed (n = 232; Fig., Supplemental Digital Content 1, http://links.lww.com/INF/A792). Predefined exclusion criteria included systemic corticosteroid treatment in the preceding 4 weeks, any chronic disease (other than asthma, allergy, or eczema), severe wheezing necessitating intensive care unit treatment, or previous participation in this study. The study was commenced only after obtaining written informed consent from the parents. The study protocol was approved by the Ethics Committee of the Turku University Hospital.
The children were randomly assigned in a double-blind manner to receive either oral prednisolone (first dose 2 mg/kg, then 2 mg/kg/d in 3 divided doses for 3 days, maximum dose 60 mg/d, Prednisolon 5-mg tablets, Leiras, Finland) or placebo after informed consent had been obtained. All patients received nebulized salbutamol according to the study protocol in the hospital.7,8 After discharge, beta2-agonists were used on demand.
The patients were examined twice daily during their hospital stay by the study physicians. After discharge, the guardian recorded the child's symptoms in a daily diary for 2 weeks after which the child was seen at the clinic. After 2 months, the parents were contacted by telephone to record any relapses necessitating a visit to a physician or hospitalization. The relapses were confirmed from the clinic and hospital records.
The predefined primary outcome was the time until ready for discharge (hospitalization time), which was defined as a duration of respiratory symptoms score >3 during the hospital stay.7,8 The respiratory symptoms score was a summed score for the degree of dyspnea (0, none; 1, mild; 2, moderate; 3, severe), type of breathing (0, normal; 1, use of stomach muscles; 2, use of intercostal muscles; 3, nasal flaring), severity of auscultatory findings on wheezing (0, none, 1, expiratory, 2, inspiratory and expiratory, 3, audible without stethoscope), and assessment of expiratory-inspiratory time (0 = 1:2, 1 = 1:1, 2 = 2:1, 3 = 3:1). Predefined secondary clinical outcomes were number of days of wheeze and cough during 2 weeks after discharge using daily diary, and readmission to the outpatient clinic or hospital for recurrent wheezing within a 2-month period after discharge.
The nasopharyngeal aspirates were analyzed for 18 viruses. Virus culture was done for adenovirus, influenza A and B viruses, parainfluenza virus (PIV) types 1–3, RSV, enteroviruses, rhinovirus, and human metapneumovirus (HMPV).2 Viral antigens were detected for adenovirus, influenza A and B viruses, PIV 1 to 3, and RSV. Levels of Ig (immunoglobulin) G antibodies specific for the same viruses (except PIV 2 and HMPV) were analyzed in paired serum samples (study entry and 2–3 weeks later), in addition to IgM antibodies for enteroviruses. In addition, HBoV IgM and IgG antibodies were analyzed from the serum samples as previously described.3 In the HBoV IgG enzyme immunoassay (EIA), ≥4-fold increase was considered diagnostic. For IgM EIA, the calculated cut-off absorbances for negative and positive IgM EIA results were 0.136 and 0.167, respectively. PCR was used for the detection of enteroviruses, rhinovirus, RSV, coronaviruses (229E, OC43, NL63, and HKU1), HMPV, HBoV, influenza A and B viruses, adenovirus, PIV 1 to 4, and polyomaviruses WU/KI.2,10 HBoV was investigated by quantitative PCR as previously described.2 Other methods have been described in detail elsewhere.2,7–9
No power calculation was made to this post hoc analysis. The efficacy of prednisolone was analyzed using generalized linear model of regression analysis (binomial distribution and log link) or logistic regression analysis. Interaction analysis between study drug (prednisolone vs. placebo) and HBoV infection (+ vs. −) was first done without adjustments (univariable model). The analysis was then repeated with adjustments to baseline differences between HBoV+ and HBoV− groups (aeroallergen sensitization, duration of preceding symptoms before hospitalization, respiratory symptom score on arrival, mixed viral infection, inhaled corticosteroid started/continued 2 weeks after discharge) (multivariable model). Because of the small sample size, a backward stepwise elimination model was used, and only significant (P < 0.05) adjustments as shown in Table 1 were kept in the model. The statistical analyses were carried out using SAS/STAT(r) software, Version 9.1.3 SP4, of the SAS System for Windows, SAS Institute Inc, Cary, NC.
Overall, 320 children were eligible for the VINKU study of which 27 (8%) refused (Fig., Supplemental Digital Content 1, http://links.lww.com/INF/A792). Of the 293 enrolled children, we included all the 232 children with complete HBoV diagnostics and who were ≤6 years of age. In all, 223 children completed the 2-week follow-up, and 204 children completed the 2-month follow-up. The median age of the 232 included children was 1.6 years (range, 0.25–6.2 years; 57 children were <1 years of age; 156 children were 1–2 years of age; and 19 children were 3–6 years of age). Of the included children, 81/231 (35%) children had specific IgE sensitization, 154 (66%) children were males, and 126/227 (56%) children had their first wheezing episode. No differences in patient characteristics were found between prednisolone and placebo groups overall (Tables, Supplemental Digital Content 2 and 3, http://links.lww.com/INF/A793 and http://links.lww.com/INF/A794).
Forty-six children were considered to have an acute HBoV infection. The HBoV diagnosis was based on serology in all 46 children. Of these, 45 (98%) children had HBoV DNA in serum and 27 (59%) had high DNA load in nasal mucus (Table, Supplemental Digital Content 2, http://links.lww.com/INF/A793). Among the HBoV-positive children, no differences in patient characteristics were found between the prednisolone and the placebo groups (Tables, Supplemental Digital Content 4 and 5, http://links.lww.com/INF/A795 and http://links.lww.com/INF/A796). HBoV-positive children, however, differed from HBoV-negative children at study entry. HBoV-affected children had less aeroallergen sensitization (7% vs. 22%, P = 0.015), lower total number of wheezy episodes (medians, 1 vs. 1, P = 0.035), longer duration of preceding symptoms (medians, 2 vs. 2 days, P = 0.028), higher respiratory symptom score on arrival (6.9 vs. 6.3, P = 0.028), more often mixed viral infection (74% vs. 29%, P < 0.0001), and less inhaled corticosteroids started/continued 2 weeks after discharge (17% vs. 35%, P = 0.018) compared with those not affected by HBoV (Tables, Supplemental Digital Content 6 and 7, http://links.lww.com/INF/A797 and http://links.lww.com/INF/A798).
In the efficacy analysis, the clinical outcomes included the time until ready for discharge, duration of wheeze or cough during 2 weeks after discharge, and relapses within 2-months after discharge. No differences were found in the univariable or multivariable interaction analyses between study drug and HBoV infection (Table 1).
Very little is known whether the response to systemic corticosteroid is related to viral etiology in acute wheezing. Systemic corticosteroids have not been clinically effective in RSV-induced bronchiolitis4–6 in slightly older wheezing children; we have found prednisolone to be clinically effective in rhinovirus-associated wheezing in post hoc analyses.7–9 We speculate that the reason why wheezing children affected by rhinovirus seem to respond to prednisolone, but not those affected by RSV or HBoV, may reside in the close link between atopic characteristics and rhinovirus infection.7–9 Thus, the corticosteroid does not seem to be effective on a virus infection itself, but rather, a susceptibility to certain viral infections, such as rhinovirus infections, may be an indicator of an inflammatory condition of the airways which may explain the efficacy. In agreement with this explanation model, there are no data to show a link between atopy or any other chronic inflammatory process and HBoV infections.
In our study, HBoV infections were carefully diagnosed using the latest IgM and IgG serology (in addition, quantitative HBoV PCR results of both NPA and serum samples were in line with serology results).2,3,11,12 Furthermore, patient characteristics were carefully studied by analyzing 17 other respiratory viruses and specific IgE levels for common food and aeroallergens and by obtaining a detailed clinical history of each child. We were, however, unable to demonstrate any efficacy of prednisolone in HBoV-positive children hospitalized for acute wheezing.
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