Prospective study of the incidence, aetiology and outcome of adult lower respiratory tract illness in the community

Background-Acute lower respiratory tract illness in previously well adults is usually labelled as acute bronchitis and treated with antibiotics withou t establishing the aetiology. Viral infection is thought to be the cause in most cases. We have investigated the incidence, aetiology, and outcome of this condition. Methods-Previously well adults from a stable suburban population consulting over one year with a lower respiratory tract illness were studied. For the first six months detailed investigations identified predetermined direct a nd indirect markers of infection. Evidence of infection was assessed in rel ation to presenting clinical features, indirect markers of infection, antib iotic use, and outcome. Results-Consultations were very common, particularly in younger women (70/1 000 per year in previously well women aged 16-39 years), mainly in the wint er months; 638 patients consulted, of whom 316 were investigated. Pathogens were identified in 173 (55%) cases: bacteria in 82 (Streptococcus pneumoni ae 54, Haemophilus influenzae 31, Moraxella catarrhalis 7), atypical organi sms in 75 (Chlamydia pneumoniae 55, Mycoplasma pneumoniae 23), and viruses in 61 (influenza 23). Seventy nine (24%) had indirect evidence of infection . Bacterial and atypical infection correlated with changes in the chest rad iograph and high levels of C reactive protein but not with (a) the GP's cli nical assessment of whether infection was present, (b) clinical features ot her than focal chest signs, and (c) outcome, whether or not appropriate ant ibiotics were prescribed. Conclusions-Over 50% of patients have direct and/or indirect evidence of in fection, most commonly bacterial and atypical pathogens, but the outcome is unrelated to the identified pathogens. Many patients improve without antib iotics and investigations do not help in the management of these patients. GPs can reassure patients of the causes and usual outcome of this self-limi ting condition.