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

There were totally 122 participants recruited from the end of September to the end of December 2003 and were followed up until the end of December 2004. Eight of these participants withdrew early as their parents found it inconvenient to attend unscheduled visit. One hundred and fourteen children aged 6 to 13 years completed the study. They were followed up for 12 to 15 months. Their baseline characteristics were tabulated in Table 1 . Among these 114 children, 16 children (14.0 %) did not report any exacerbations or respiratory illnesses. Children with respiratory illnesses were younger than children without respiratory illnesses (p<0.05) and there was greater proportion with normal pulmonary lung function test at the time of recruitment (p=0.02). Fifteen children had reported 20 episodes of mild respiratory illness with symptoms with remaining 83 children had experienced ≥1 episode of respiratory illnesses with symptoms score >3 and the maximum number of episodes per children was seven in two children. There were a total of 211 episodes with a symptom score >3. Nasal swab specimens were obtained in 166 and the interval between onset of respiratory symptoms and nasal swab collection ranged from 0.5 to 6 days. Nasal swab specimens were not available in the remaining 45 episodes as the children attended general practitioner (GP) instead. There were 74 episodes of mild respiratory illnesses with symptom score ≤3 reported in these 83 children that were also managed by GP. The distribution of these episodes of respiratory illnesses among the children was illustrated in Fig. 1 . Thus, there were a total of 305 episodes of respiratory illnesses including asthma and non-asthma related episodes in our study cohort over the 14-month study period. The mean number of asthma exacerbations, other respiratory illnesses, and all episodes as diagnosed at unscheduled visits were 0.69, 1.6, and 2.29 per person-year, respectively.