Patients with chronic obstructive pulmonary disease frequently develop respiratory infections. Occasionally the increased sputum volume and purulence fail to resolve after a course of an appropriate antibiotic, and hospital admission is often required. If the patient remains unwell with breathlessness and wheeze, continuing respiratory infection is presumed. Patients often receive repeated courses of antibiotics, which disturb the oropharyngeal flora and facilitate colonisation or invasion of the lung by different organisms or antibiotic resistant strains of the original organism.In up to 40% of patients, however, sputum cultures show no growth.1 Even when an organism is isolated from sputum its pathogenic importance may be uncertain, and the clinical response to an appropriate antibiotic is often disappointing.2. Sometimes more than one type of organism is found, and the importance of each is difficult to determine. Doctors often have to choose between empirical antibiotic treatment and further attempts to make a microbiological diagnosis.

Haemophilus influenzae and Streptococcus pneumoniae are the commonest organisms identified in the sputum during exacerbations of chronic obstructive pulmonary disease,^1,3 accounting for 43% and 25% of positive cultures respectively in one study.1 Patients with the condition are often colonised with H influenzae,^4,5 and exacerbations frequently coincide with endogenous or …