Community-acquired polymicrobial pneumonia in the intensive care unit: aetiology and prognosis

The prospective observational study included 362 consecutive adult patients with CAP admitted to the ICU within 24 hours of presentation; 196 (54%) patients had an established aetiology.Polymicrobial infection was present in 39 (11%) cases (20% of those with defined aetiology): 33 cases with two pathogens, and six cases with three pathogens. The most frequently identified pathogens in polymicrobial infections were Streptococcus pneumoniae (n = 28, 72%), respiratory viruses (n = 15, 39%) and Pseudomonas aeruginosa (n = 8, 21%). Chronic respiratory disease and acute respiratory distress syndrome criteria were independent predictors of polymicrobial aetiology. Inappropriate initial antimicrobial treatment was more frequent in the polymicrobial aetiology group compared with the monomicrobial aetiology group (39% vs. 10%, P < 0.001), and was an independent predictor of hospital mortality (adjusted odds ratio = 10.79, 95% confidence interval = 3.97 to 29.30; P < 0.001). The trend for higher hospital mortality of the polymicrobial aetiology group compared with the monomicrobial aetiology group (n = 8, 21% versus n = 17, 11%), however, was not significantly different (P = 0.10).Polymicrobial pneumonia occurs frequently in patients admitted to the ICU. This is a risk factor for inappropriate initial antimicrobial treatment, which in turn independently predicts hospital mortality.Community-acquired pneumonia (CAP) remains a common and potentially life-threatening condition. Among patients hospitalised by CAP, the rates of severe CAP range from 6.6 to 16.7% [1].The pathogens causing CAP may vary according to geographic area and underlying risk factors. Appropriate initial antimicrobial treatment has been repeatedly shown to be crucial for the outcome in severe infections. The knowledge of pathogen patterns causing CAP as the basis for the selection of such treatment is therefore crucial. Some studies have revealed that more than one causative microorganism was present in a con