Community-acquired pneumonia through Enterobacteriaceae and Pseudomonas aeruginosa: diagnosis, incidence and predictors

The aim of the present study was to determine the relevance of the presence of Enterobacteriaceae (EB) and Pseudomonas aeruginosa (PA) in patients with community-acquired pneumonia (CAP) and how the true incidence of these pathogens can be assessed. Based on prospective data from 5,130 patients with CAP included in the German Competence Network for Community-Acquired Pneumonia (CAPNETZ), the incidence, clinical characteristics, outcome and predictors of patients with CAP due to EB and PA were studied applying strict case definitions. The incidence of EB was 67 (1.3%) out of 5,130, including 27 patients with bacteraemia. PA was found in 22 (0.4%) out of 5,130 patients. These microorganisms were judged to be indeterminate pathogens in an additional 172 and 27 isolates, respectively. Patients with indeterminate pathogens differed considerably from those with definite isolates in terms of clinical presentation, comorbidity, pneumonia severity and outcome. Independent risk factors for EB included cardiac and cerebrovascular disease, and for PA chronic respiratory disease and enteral tube feeding. The 30-day mortality was significantly higher in patients with definite pathogens. In the present large population, the incidence of CAP due to EB/ PA was low. The risk of the presence of these pathogens can be assessed using several predictors, which may identify those patients in need of an extended diagnostic work-up and initial antimicrobial treatment.