Novel concepts in virally induced asthma

Infections have been recognized to be a cause of asthma exacerbations for over 100 years. In his landmark textbook that heralded modern medicine, Sir William Osler noted that among other asthma exacerbating factors such as allergens and environmental changes, "every fresh cold" could induce a paroxysm of disease [1]. During Osler's time, viruses had not yet been isolated as infectious agents, and in the first half of the twentieth century, the "colds" or upper respiratory tract infections that caused worsening of asthma symptoms were largely presumed to be caused by a hypersensitivity or allergy to the bacteria that were considered to be responsible for these infections [2]. This concept was accepted by some physicians who attempted to desensitize patients who experienced asthma exacerbations following respiratory tract infections by administering allergy shots that contained bacterial extracts [3]. Detractors of the bacterial allergy theory pointed out that while extracts of environmental allergens such as pollens or animal dander could produce positive immediate skin test results in sensitive subjects, bacterial extracts did not provoke such hypersensitivity reactions [4].Despite the inability of bacterial skin testing to confirm hypersensitivity to these organisms, immunotherapy containing bacterial extracts was used substantially in the prophylaxis against asthma exacerbations from the 1920s to the late 1950s [4,5]. Physicians who used this bacterial immunotherapy strategy reported that the majority of their patients had symptomatic improvement on this treatment [3,5]. However, several well controlled trials in the late 1950s and early 1960s revealed that immunotherapy to bacterial antigens was no more effective than placebo, and there was a call to end this practice that was widely heeded by the medical community [5-7]. A further blow to the concept of bacterial allergy came with randomized controlled-trials in the 1970s and 1980s which showed that antibiotic a