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

We performed a prospective cohort study from September 2003 to December 2004 to delineate attributing the effect of different respiratory viral infections including newly discovered ones to asthma exacerbations in children in Hong Kong. One hundred and fourteen children aged 6–14 years with chronic stable asthma and on regular inhaled steroid were monitored for respiratory symptoms over a full calendar year from recruitment. They would attend the study clinic if peak expiratory flow rate decreased to below 80% of their baselines, if they met a predefined symptom score, or if parents subjectively felt them developing a cold. Virological diagnosis using virus culture, antigen detection, and polymerase chain reaction methods on nasal swab specimens would be attempted for all these visits irrespective of triggers. Physician diagnosed outcome of each episode was documented. Three hundred and five episodes of respiratory illnesses were captured in the cohort. Nasal specimens were available in 166 episodes, 92 of which were diagnosed as asthma exacerbations, and 74 non-asthma related episodes. Respiratory viruses were detected in 61 of 166 episodes (36.7%). There was no significant difference in virus detection rate between asthma exacerbations (32 out of 97 episodes, 34.8%) and non-asthma respiratory illnesses (29 out of 79 episodes, 39.2%). Although newly discovered respiratory viruses were identified in these episodes, rhinovirus was the commonest organism associated with both asthma exacerbations and non-asthma related episodes. Plausible explanations for much lower virus detection rate than previously reported include improved personal hygiene and precautionary measures taken during respiratory tract infections in the immediate post-severe acute respiratory syndrome period together with a significant contribution of other adverse factors like environmental air pollution. We conclude that not all viral infections in children with asthma lead to an asthma exacerbation and the attributing effect of different triggers of asthma exacerbations in children vary across different time periods and across different localities

Ethnic differences in time trends in asthma prevalence in New Zealand: ISAAC Phases I and III.

SETTING: The International Study of Asthma and Allergies in Childhood (ISAAC) Phase III survey, New Zealand. OBJECTIVE: To assess the prevalence of asthma symptoms and time trends by ethnicity between ISAAC Phase I (1992-1993) and Phase III (2001-2003). DESIGN: Information on asthma symptoms and environmental exposures was collected in children aged 6-7 years (n = 10,873) and adolescents aged 13-14 years (n = 13,317). RESULTS: In children, the prevalence of current wheeze was 28.5% in Māori (prevalence odds ratio [POR] = 1.49, 95%CI 1.32-1.68), and 25.2% in Pacific Islanders (POR 1.28, 95%CI 1.07-1.54) compared with 20.7% in Europeans/Pakeha. In adolescents, 29.9% of Māori (POR = 1.13, 95%CI 1.03-1.23) and 20.8% of Pacific Islanders (POR 0.74, 95%CI 0.62-0.87) experienced current wheeze compared to 28.6% of Europeans/Pakeha. Between Phases I and III, the prevalence of current wheeze increased significantly by 0.49%/year in Pacific Islanders, increased non-significantly by 0.12%/year in Māori, and decreased significantly by 0.25%/year in Europeans/Pakeha children. In adolescents, the prevalence of current wheeze increased by 0.05%/year in Pacific Islanders and decreased by 0.33%/year in Europeans/Pakeha and by 0.07%/year in Māori. CONCLUSION: Ethnic differences in asthma symptom prevalence in New Zealand have increased. The reasons for this are unclear, but may reflect inequalities in access to health services