Controlled study of respiratory viruses and wheezing.

W heezing in early childhood is common, occurring in approximately 50% of children before the age of 6 years. 1 Understanding the role of respiratory viruses in triggering acute wheezing in children has been compromised by the lack of comparison groups in previous studies. 2 The objective of this study was to investigate the association (using a control group) of two common viruses—influenza virus and respiratory syncytial virus (RSV)—with acute wheezing among children, aged 1–7 years, with a past history of wheezing. METHODS Children, aged 1–7 years, with two or more previous wheezing episodes, were enrolled from a paediatric community practice and an emergency department during two consecutive winters (1997/1998, 1998/1999) into this concurrent case– control study. Cases had previous wheezing and current symptoms of an upper respiratory infection and acute wheezing (clinical score of at least 1). Controls had previous wheezing and current symptoms of an upper respiratory tract infection, without acute wheezing (clinical score of 0) at the time of enrolment or within the week following enrolment. Children were excluded if they had received immunisation for influenza in the year of enrolment. The study was approved by the Hospital for Sick Children Research Ethics Board, and informed parental consent was obtained. Baseline characteristics were collected and wheezing severity was graded using a clinical score (minimum to maximum range: 0–10). Nasopharyngeal swab specimens were collected and examined for influenza viruses A and B and RSV by immunofluorescence microscopy (antibodies from Light Diag-The odds ratio and 95% confidence interval were determined for influenza virus and RSV in children with acute wheezing (cases) relative to children with upper respiratory symptoms alone (controls). Separate analyses were under-taken for community cases versus controls, and all cases (community and emergency cases) versus controls. RESULTS Table 1 shows baseline characteristics. Table 2 shows the association between acute wheezing and virus infection. For influenza virus, the odds ratio indicates that infection is not associated with acute wheezing. The adjusted odds ratio (all cases versus controls) for the risk of acute wheezing in those with influenza was 0.52 (95% confidence interval, 0.27 to 1.03). For RSV, the odds ratio indicates that infection is associated with a threefold increase in the risk of acute wheezing. Children with influenza virus (n = 43) and RSV (n = 58) were compared. Children with influenza virus were older (median age 3.6 years v 2.4 years, p = 0.002), had a lower …