Effect of influenza A virus infection on acid-induced cough response in children with asthma.

Although it is well-known that some types of respiratory viral infections cause airway hyperresponsiveness in humans, the effect of viral infection on the cough threshold in asthmatics is not known. We, therefore, evaluated the effects of naturally-acquired influenza A virus infection on the cough threshold to inhaled acid in children with asthma. Twelve children with asthma (9 boys and 3 girls, mean +/- SEM age of 10.8 +/- 0.6 yrs), who had naturally-acquired influenza A virus infection in winter (January-February, 1992) during an epidemic of influenza A (H1N1), were enrolled in this prospective, uncontrolled study. All patients underwent acetic acid (AA) inhalation challenge 2, 4 and 6 weeks after the influenza infection. The cough threshold values (the lowest concentrations of AA eliciting coughs) after 2, 4 and 6 weeks of the illness were 3.7 +/- 0.9, 5.3 +/- 1.0 and 8.1 +/- 1.4% (mean +/- SEM), respectively. Cough threshold values 4 or 6 weeks after the illness improved significantly over that at 2 weeks (p < 0.05 and p < 0.01, respectively). In contrast, baseline forced expiratory volume in one second did not change throughout the study. These results indicate that influenza A virus infection attenuates the cough threshold independently of airway obstruction in children with asthma. The enhanced cough response following virus infection is probably mediated by damage to the airways epithelium.