Abstract

Summary. The objective of this study was to identify wheezing recurrences and related risk factors in two groups of infants with bronchiolitis: respiratory syncytial virus (RSV) (+) and RSV (-) as determined by RSV enzyme immunoassay. A 1 -year prospective cohort study was conducted with infants younger than 2 years old. Follow-up was made monthly, by a clinical visit and/ or by telephone, checking the number of wheezing episodes per month and possible related risk factors. There were 96 subjects enrolled, of whom 77 reached complete follow-up: 36 were RSV(+) (46.8%), and 41 were RSV (-) (53.2%). In the RSV (+) group, there were 17 males (47%), vs. RSV (-) with 30 males (73%) (P<0.05); 22 RSV (+) (61%) were admitted to hospital, vs. 14 RSV (-) (34%) (P< 0.05). Mean age was not significantly different in both groups. The mean number of recurrences was 3.36 episodes/infant/year in the RSV (+) and 2.34 in the RSV (-) group (P= 0.06). Crude relative risk (RR) for a new recurrence of an obstructive episode was 1.33 (95% Cl, 0.99-1.79). After adjustment for several potential confounders, the RR was 1.41 (95% Cl, 1.03-1.93). Hospitalization stay was longer in the RSV (+) than the RSV (-) group (P<0.05). In the RSV (+) group, patients who had been hospitalized showed more recurrences (4.18) than those with outpatient treatment (2.07) (P<0.05); this difference did not exist in the RSV (-) group. The related risk factors for recurrent wheeze in the RSV (-) group were male gender, number of siblings, and daycare attendance (P<0.05). In the RSV (+) group, the risk of recurrent wheeze was only increased by admission to hospital during the acute bronchiolitis episode (P<0.05). We speculate that there may be a higher rate of increased airway reactivity and/or preexisting diminished lung function in RSV (+) infants requiring hospitalization for their initial illness. In conclusion, RSV-proven bronchiolitis, particularly in those infants who are hospitalized, is associated with a higher recurrence of wheezing episodes in the subsequent 12 months. Other factors appear to account for recurrent wheeze in the RSV (-) group. © 2003 Wiley-Liss, Inc.