Relationship of bacterial and viral infections to exacerbations of asthma.

Fifty-one asthmatic patients were followed for up to 18 months. During this time 111 exacerbations of wheeze were recorded. Involvement by pathogenic respiratory bacteria and viruses was looked for directly by culture and indirectly by antibody studies. Proof of infection was found in only 12 (10.8%) of the 111 exacerbations. Only eight patients provided sputum samples. Potential bacterial pathogens were found in four. Viruses were isolated in four of 27 exacerbation specimens; significant rises in specific viral antibody titres occurred in three. Six patients developed precipitating antibody to respiratory bacteria over the study but only one in relation to an exacerbation. The study therefore indicated that the great majority of exacerbations of asthma in these patients were not due to respiratory tract infection.