Epidemiology, associated factors and outcomes of ICU-acquired infections caused by Gram-negative bacteria in critically ill patients: an observational, retrospective study

BACKGROUND Gram-negative bacteria are increasingly responsible for nosocomial infections, including ICU-acquired infections. Due to high virulence, rate of multi-drug resistance and limited availability of new agents, these infections create cumbersome clinical burdens, making it important to reduce the risk of their occurrence. The aim of the study was to assess epidemiology-related factors and outcomes of Gram-negative, ICU-acquired infections in a cohort of medical-surgical patients. METHODS A retrospective survey was conducted on all patients admitted to a mixed ICU from January 2012 to December 2013. 'ICU-acquired infections' were defined as new infections acquired no less than 48 h after ICU admission. Diagnosis was made according to the Centers for Disease Control and Prevention National Healthcare Safety Network (CDC/NHSN) criteria. Differences across patients who did and did not acquire a Gram-negative infection were tested regarding age, sex, body mass index, medical or surgical admission, cardiovascular comorbidities, chronic obstructive pulmonary disease, diabetes, end-stage renal failure, co-existing tumours and prophylactic anti-fungal treatment. Multivariate analysis was used to assess the independency of these associations. Finally, differences in ICU-mortality, ICU-length of stay and duration of mechanical ventilation were tested across patients with and without new, ICU-acquired, Gram-negative infections. RESULTS Of 494 patients admitted to the ICU, 46 (9.3 %) acquired an infection 48 or more hours after admittance. In 30/46 patients (65.2 %) the isolated bacterium was Gram-negative. Univariate analysis showed that clinical factors associated with new ICU-acquired Gram-negative infections were medical admission (p < 0.001, 95 % CI 0.59 - 0.29, OR = 0.13), chronic kidney disease (p = 0.018, 95 % CI 1.20 - 7.34, OR = 2.98) and prophylactic antifungal therapy (p < 0.001, 95 % CI 1.91 - 9.79, OR = 4.33). At multivariate analysis, only medical admission and prophylactic antifungal therapy were significantly associated with ICU-acquired Gram-negative infections. Higher ICU-length of stay and longer duration of mechanical ventilation were associated with these infections while ICU-mortality did not significantly differ. CONCLUSIONS ICU-acquired Gram-negative infections were common in a cohort of mixed medical-surgical patients. Only medical admission and anti-fungal prophylaxis were found to be independently associated with these infections; they were not found to have a significant effect on ICU-mortality.