Critical review of microbiological data and methods in diagnosis of lower respiratory tract infections

A review is presented of the microbiological data, and the methods for obtaining these data, which are relevant for the diagnosis of lower respiratory tract infection. The necessity for adequate information exchange between the microbiology laboratory and the clinic is stressed. Once the specimen (usually sputum) has reached the laboratory, it is screened macroscopically and microscopically for adequacy, and cultures are set up. Many patients with acute community-acquired pneumonia (CAP) have no sputum, and some produce purulent sputum containing no obvious infecting micro-organisms. Despite modern microbiological techniques, only 110 out of 250 acute CAP patients had positive bacteriological cultures and 41 more yielded only positive serological results, so that an aetiological diagnosis was reached in 60%. Invasive methods of specimen collection (bronchoscopy, BAL, protected brush, etc) have also been studied, together with quantitative bacterial counting, but the results have not yielded so much useful information that these procedures can be unreservedly recommended. Molecular biological methods (DNA probes, PCR, etc) are only now becoming available. The bacteriological findings in patients with acute CAP have been compared with those in acute exacerbations of chronic bronchitis (CB), and several differences have emerged in the order of frequency of occurence. H. influenzae is in first place with exacerbations of CB, but is second to S. pneumoniae in acute CAP. The latter occupies third position in CB, with Moraxella catarrhalis second. The role of Chlamydia pneumoniae in acute CAP is not yet clear, but the serological results suggest an association in 42 out of 147 patients tested (29%), 15 of whom also had positive bacteriological cultures.(ABSTRACT TRUNCATED AT 250 WORDS)