A median of two blood cultures, research use one urine culture, and one endotracheal aspirate culture were obtained for both the culture-negative and the culture-positive patients.Table 3Cultures performed.Table Table44 features the microbiology. Gram-positive bacteria were isolated in 257 patients (25.7%) while Gram-negative bacteria were isolated in 390 patients (39.0%). Among these patients, 196 (19.6%) had only Gram-positive infections, 329 (32.9%) only Gram-negative infections, while 61 (6.1%) had mixed Gram-positive and Gram-negative infections. Staphylococcus aureus and Klebsiella pneumonia were the commonest Gram-positive and Gram-negative microorganisms respectively.Table 4Bacteria isolated.Patient outcomes are presented in Table Table5.5.

Culture-negative patients had a shorter duration of hospital stay, and lower ICU mortality and hospital mortality (35.9% versus 44.0%, P = 0.01) than culture-positive patients.Table 5Outcomes.Table Table66 details the variables associated with hospital mortality. While culture positivity was associated with higher mortality on univariable analysis, it did not feature as an independent predictor of mortality after accounting for other covariates on logistic regression analysis. The same applies to the administration of inappropriate antibiotics on the day of ICU admission. Multivariable analysis revealed the following independent predictors of mortality: age, time from hospitalization to ICU admission, lung, bone and joint infections, infective endocarditis, primary bacteremia, Acute Physiology Score, coagulation and hepatic failures, and mechanical ventilation on the day of ICU admission.

The logistic regression model fitted well and there was no multicollinearity. In a separate analysis including specific microorganisms, Pseudomonas aeruginosa was the only pathogen which, when isolated independently, increased mortality (odds ratio (OR) 2.02, 95% CI 1.08 to 3.79, P = 0.03).Table 6Predictors Batimastat of hospital mortality by univariable and multivariable logistic regression analyses.Among the culture-positive patients, 265 were nonbacteremic while 321 were bacteremic. Hospital mortality was similar in both subgroups. The nonbacteremic but culture-positive subgroup had a higher mortality rate than the culture-negative group but this was not statistically significant; the bacteremic subgroup had a significantly higher mortality rate than the culture-negative group (Figure (Figure1).1). Again among culture-positive patients, 467 received appropriate antibiotics on the first day of ICU stay while 119 did not. Hospital mortality was higher in the latter subgroup.