There is strong epidemiological evidence that respiratory viral infections are associated with 80–85% of asthma exacerbations in children. There is less evidence in adults, but the available data suggest viruses are associated with around two-thirds to three-quarters of exacerbations in adults. These associations include severe exacerbations requiring hospitalisation. The most common viruses detected in these studies were rhinoviruses, accounting for two-thirds of viruses detected. Asthmatics have increased susceptibility to respiratory virus infection and have recently been shown to have profoundly defective interferon-beta responses to virus infection, resulting in increased virus replication. Atypical bacterial infections are also associated with chronic asthma and asthma exacerbations and a recent study indicates antibiotic therapy active against atypical bacteria is effective in treatment of exacerbations. Recent data also indicates asthmatics are at increased risk of invasive pneumococcal disease, suggesting they may also have impaired antibacterial immunity. Research is urgently required to determine whether augmenting anti-infective immunity is beneficial in the treatment/prevention of asthma exacerbations. More recent data also implicates viruses in the majority of exacerbations of chronic obstructive pulmonary disease. Studies are also required investigating anti-infective host defence in chronic obstructive pulmonary disease
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