October 27, 2011 (San Francisco, California) — Although infections caused by multidrug-resistant organisms have been steadily increasing, they are not associated with increasing mortality among patients in the surgical intensive care unit (ICU), according to a prospective analysis performed at the University of Virginia Health Systems in Charlottesville and reported at the American College of Surgeons (ACS) 97th Clinical Congress.
Ten-Year Trend in Antibiotic-Resistant Pathogens Tracked
"With a progressive rise in the severity of illness seen in ICU patients, there is an increase in total infections and in resistant organisms, but their relationship with outcomes has been unclear," said Laura Horst Rosenberg, MD, who presented the study. She and her colleagues hypothesized that, in parallel, an increase in overall mortality would be observed among patients in their surgical ICU.
They prospectively identified all infections acquired over a 10-year period in their surgical ICU. Crude in-hospital, all-cause mortality data were obtained by using a prospectively collected ICU database. Trends in rates were compared by using linear regression.
A total of 799 resistant pathogens were identified (257 gram-positive, 542 gram-negative) from a total of 3024 isolated pathogens associated with 1493 ICU-acquired infections. The resistant organisms were oxacillin- or methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus species (VRE), and gram-negative organisms resistant to all members of any single major class of antimicrobials.
Compared with patients whose infections were caused by pathogens sensitive to antibiotics, patients with ICU-acquired resistant pathogens had a higher body mass index (P = .007), higher Acute Physiology and Chronic Health Evaluation (APACHE) II scores (P < .001), more transplantation procedures (P < .001), more transfusions (P < .001), more hemodialysis (P < .001), longer duration of antibiotic therapy (P < .001), and longer length of stay (P < .001). They also had higher mortality rates (33% vs 23%; P < .001), Dr. Rosenberg reported.
The most frequently identified resistant gram-positive and gram-negative pathogens were MRSA and Pseudomonas aeruginosa, respectively, which constituted 55% and 27% of the total resistant populations. The pathogens were most commonly isolated from the lung, blood, and urine.
Crude Mortality Rates Decreased
Although resistant infections carried higher mortality rates than those associated with sensitive pathogens, the overall crude mortality rate in the surgical ICU declined steadily over time, from 9.3% in 2000 to 5.4% in 2009.
"Linear regression analysis of quarterly rates revealed a significant divergence in trends between increasing total resistant infections and percentage resistant infections when compared to a decreasing mortality," Dr. Rosenberg reported.
"We believe the impact of a resistant infection provides only a small contribution toward overall mortality," she said.
Soumitra R. Eachempati, MD, from Weill Cornell Medical College in New York, New York, called the report "an excellent 10-year retrospective study that concluded multidrug resistant infections are not associated with increased mortality. In fact, they found mortality was decreased in the surgical ICU…. The data appear to be thorough and well-researched, and I agree with the researchers' conclusions," he said.
Dr. Eachempati noted, however, that certain factors might not have been considered in the analysis. For example, sensitivity to pathogens can change over time, thus altering their classification. "Going forward," he suggested the investigators evaluate the influence on attributable, rather than crude, mortality.
Dr. Rosenberg and Dr. Eachempati have disclosed no relevant financial relationships.
American College of Surgeons (ACS) 97th Annual Clinical Congress; Presented October 25, 2011.
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