Viruses and asthma exacerbations

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Abstract
For many years general opinion has been that upper respiratory viruses were the cause of the common cold but were able to produce serious complications only in infants, the elderly, and immunocompromised subjects. Although a connection between upper respiratory infections and asthma had long been recognised, the potential importance of the association was probably underestimated until relatively recently when it was shown that, in the community, 85% of asthma attacks in children1 and 44% in adults2 are precipitated by upper respiratory infections. The last two years have also provided evidence that “common cold” viruses can also induce severe asthma. In a time trend analysis comparing the seasonal patterns of respiratory infections and hospital admissions for asthma in children and adults,3 strong correlations were observed in both groups. The major factor determining paediatric admissions was school attendance, and the peaks of both respiratory infections and asthma admissions occurred at the beginning of school terms. In these studies rhinovirus infections are numerically the most important, accounting for 60% of viruses detected. In another study Teichtahl et al documented the incidence of respiratory tract infections in adults requiring admission to hospital for acute asthma.4 Thirty seven percent of their patients recruited during one year had evidence of infection, and viruses were identified by culture and/or serology in 80% of these cases. A similar time trend analysis was used to investigate the possible contribution of virus infections to asthma mortality.5Winter peaks in asthma mortality were observed in children under five and in adults over 45 years, suggesting that virus infections also precipitate asthma deaths in these age groups. Interestingly, in asthmatic subjects aged 5–44 years there was a strong summer peak (July/August). The reasons for this are presently unclear but …