Gram-positive nosocomial infections in a general ICU: searching for a clue

Introduction

The pattern of nosocomial pathogens has changed gradually since the mid 1980s and Gram(+) aerobes are the leading cause of infection in many ICUs today. Despite this trend there are still no firm recommendations for empiric Gram(+) antimicrobial coverage in patients with severe nosocomial infections.

Methods

A historical cohort study was conducted and included all cases of documented nosocomial infections in our general ICU for a 1-year period (November 2006–November 2007). Data on demographic characteristics, primary diagnosis, comorbidity, number of indwelling devices, previous microbial isolates and current antibiotics were cross-tabulated according to the presence and type of Gram(+) pathogens isolated. For the identified most likely risk factors, separate contingency tables were constructed and analyzed.

Results

Sixty-six patients (39.05% of 169 with documented nosocomial infections) with Gram(+) isolates were identified. Methicillin-resistant Staphylococcus epidermidis (MRSE) (34.85%) and Enterococci (25.76%) were most commonly isolated, followed by methicillin-resistant Staphylococcus aureus (MRSA), methicillin-susceptible S. epidermidis (MSSE), Streptococci, and methicillin-susceptible S. aureus (MSSA). In eight (12.12%) of these 66 patients the same pathogen was isolated more than once and in 14 patients (21.21%) more than one Gram(+) pathogen was present during his/her ICU stay. There were no significant differences between the groups according to demographic characteristics. The following independent risk factors for Gram(+) nosocomial infection were identified – for MRSE, gunshot wound, chronic obstructive pulmonary disease comorbidity, previous isolation of both Acinetobacter spp. and Pseudomonas spp, previous/current treatment with carbapenem; for Enterococcus spp., billiary peritonitis, previous/current treatment with the combination cefoperazone–sulbactam; for MRSA, clinical uroinfection; for MSSE, previous/current treatment with combination first/second-generation cephalosporin–metronidazole; for MSSA, neurologic injury. Surprisingly the number of indwelling devices was not linked with increased risk of coagulase-negative staphylococcal infections, nor there was found a long latent period for their clinical manifestation.

Conclusion

Exploratory hypotheses for further larger sample conformations have been generated. Whether some of these are pertinent to a particular ICU or could be generalized remains to be elucidated. Identification of associated risk factors for Gram(+) nosocomial infections would aid initial antibiotic choice in such patients at risk.