'Atypical' bacteria are a common cause of community-acquired pneumonia in hospitalised adults

Objectives. To assess the proportion of cases of community· acquired pneumonia caused by 'atypical' bacteria, inclUding the recently discovered Chlamydia pneumoniae, and to compare the clinical, radiographic and laboratory features of patients with and without 'atypical' bacteria.Methods. A prospective serological study was carried out on consecutive adult pneumonia patients from July 1987 to July 1988. Acute and convalescent sera were tested in batches for antibodies against Legionella pneumophila serogroup 1, C. pneumoniae, Chlamydia psittaci, Coxiella burnetii (phase-2 antigen) and Mycoplasma pneumoniae (lgG and IgM). Records and chest radiographs were examined retrospectively.Results. Acute and convalescent sera were available from 113 patients. The records of 4 patients could not be traced and 17 patients did not fulfil the inclusion criteria. Thirty-two of these 92 patients (35,9%) were found to be infected with 'atypical' bacteria. The two most common organisms were C. pneumoniae (20,7%) and L. pneumophila (8,7%). There. were no differences in the clinical and radiographic features of patients with and without 'atypical' bacteria. Clinicians prescribed erythromycin or tetracyclines with equal frequency in the two groups.Conclusions. 'Atypical' bacteria, especially C. pneumoniae, are a common cause of community-acquired pneumonia in adults in South Africa. This is the first demonstration of an aetiological role of C. pneumoniae in this country. We confirmed the finding of other studies that there are no clinical, radiographic or laboratory features characteristic of 'atypical' bacterial infection in hospitalised patients. This has major implications for therapy, as these organisms respond to erythromycin and tetracyclines, but· not to β-lactam antibiotics