Is respiratory viral infection really an important trigger of asthma exacerbations in children?

Lee, So-lun; Chiu, Shui-seng Susan; Malik, Peiris Joseph S.; Chan, Kwok-hung; Wong, Hing-sang Wilfred; Lau, Yu-lung

Each child was given an asthma diary chart and a peak flow meter (Mini-Wright AFS Low range peak flow meter) during the run-in period. Parents and children were taught on data entry, use of peak flow meter, and record twice daily peak expiratory flow rate (PEFR) and any upper and lower respiratory symptoms for 2 weeks as baseline. [14] (Appendix). The diary chart was then reviewed and the child's calculated 80% baseline PEFR was recorded on a new log sheet. Parents were instructed to start to record PEFR twice daily and respiratory symptoms in a new log sheet when the symptoms scored >3. They were to call the research nurse if PEFR fell to below 80% of the child's baseline, if total upper or lower respiratory symptom score totalled ≥4, or if parents subjectively felt the child was developing a cold even though PEFR fell by <20% of baseline. An unscheduled clinic visit would be arranged within 48 h. During the unscheduled visit, upper and lower respiratory symptoms and physical signs were recorded. An asthma exacerbation was defined as a fall in morning PEFR to below 80% of baseline in the absence of expiratory wheeze for ≥2 two consecutive days. The presence of wheeze detected by the attending paediatrician at the time of visit (Lee SL/Chiu SS), or an increase in the use of shortacting beta 2 agonists on at least two occasions per day for ≥2 consecutive days. Diagnoses other than asthma exacerbation were also captured. Chest radiograph were ordered if clinically indicated. Respiratory secretions from children were obtained using nasal swabs. The cotton-tipped swab was inserted into the nostril for 2 to 3 cm and rotated three times against the respiratory epithelial surface of the nasal cavity. Once collected, the specimen was put in a virus transport medium and immediately transported to the microbiology laboratory for processing. The child was treated as appropriate. The parents and child continued to record daily PEFR and symptoms in the subsequent 2 weeks or longer until symptoms subsided completely. Follow-up visits would be arranged. All participants also attended scheduled clinic visit every 3 months. At each scheduled visit, all respiratory symptoms at follow-up or any respiratory problems in between visits that were not reported would be recorded.