To evaluate the prevalence of respiratory viruses Mycoplasma pneumoniae and Chlamydophila pneumoniae and gain insight into their seasonal circulation pattern in children with acute asthma exacerbations in a temperate southern hemisphere region.

Patients hospitalized between 3 months and 16 years of age were included in a 1‐year prospective, observational, cross‐sectional study. Respiratory secretions were collected and the presence of different viruses and atypical bacteria analyzed by immunofluorescence and polymerase chain reaction.

Two hundred nine patients (118 females) aged (mean ± SD) 4.4 ± 4 years were included. A potential causative agent was detected in 78% of the patients. The most frequently detected viruses were respiratory syncytial virus (HRSV) (n = 85; 40%) and rhinovirus (HRV) (n = 52; 24.5%); M. pneumoniae and C. pneumoniae were detected in 4.5% and 2% of the cases, respectively. Patients with HRSV (vs. HRV) were hospitalized for a longer time (6.7 vs. 5.2 days, P = 0.012), required more days of oxygen supply (5.1 vs. 3.4, P = 0.005), had a longer duration of the exacerbation before hospitalization (3.6 vs. 1.9 days, P = 0.001) and were younger (3.7 vs. 5.1 years, P = 0.012). Three peaks of admissions were observed. A first peak (early autumn) caused by HRV, a second peak (winter) caused mainly by HRSV and a third one (spring), caused by HRSV, an increase in HMPV together with a second outbreak of HRV.

Children with an acute asthma exacerbation presented a high prevalence of respiratory viruses. Most hospitalizations corresponded to seasonal increases in prevalence of HRV and HRSV. Pediatr Pulmonol. 2010; 45:619–625. © 2010 Wiley‐Liss, Inc.