The extent of microbiological testing is associated with alteration of antibiotic therapy in adults with community-acquired pneumonia.

The aim of this study was to explore the relationship between the extent of microbiological testing and the frequency of antibiotic alteration in adults hospitalised with community-acquired pneumonia (CAP). We retrospectively studied 283 immunocompetent patients hospitalised with CAP. Information on microbiological testing and prescribed antibiotics was obtained. Patients were grouped according to the number of different microbiological tests performed within the first 2 days of admission (0-5 tests). Alteration rates were compared between these groups. Antimicrobial alteration was defined as a switch at day 3 of hospital stay to (1) a narrower spectrum antibiotics, or (2) a different class of antibiotics, or (3) a switch from dual therapy to monotherapy (4) or discontinuation of antibiotic treatment because the indication for antibiotic treatment did no longer exist. For each additional test performed, a stepwise increase in percentage of patients with altered antibiotic regimen ranging from 0 to 59% (p = 0.001) was found. Multivariate logistic regression analyses showed that performing PCR assay for atypical pathogens was most strongly associated with any alteration of antibiotic treatment (OR 2.6 (95% CI 1.4-4.9)) and with changes in atypical coverage specifically (OR 3.1 (95% CI 1.6-6.0). The extent of microbiological testing was positively associated with antibiotic alteration in adults hospitalised with CAP. Antibiotic treatment was most likely to be altered in patients in whom PCR assay for atypical pathogens was performed.