Evolving pathogens in the surgical intensive care unit: a 6-year experience

Nosocomial infections in the intensive care unit (ICU) are well-known causes of morbidity and mortality in critically ill patients. Further complicating this issue is the ever-increasing number of multidrug-resistant pathogens. This study was designed to investigate and document changing microbial trends within the Los Angeles County/University of Southern California Medical Center surgical ICU (SICU), including drug-resistant pathogens.

A 6-year retrospective cohort study of all patients 18 to 85 years old with positive blood, urine, or sputum cultures admitted to an urban, level 1 trauma/SICU. Patients were identified through the Los Angeles County/University of Southern California Medical Center epidemiological records and computerized ICU database. The entire data set was analyzed according to pathogen classification schemes, culture date, type of infection, and with some patient characteristics including sex, average age, and Acute Physiology and Chronic Health Evaluation II score. Two groups were created to analyze changing trends: a past group (2000-2002 cultures) and a present group (2003-2005 cultures). Any repeated cultures were excluded, as was coagulase-negative Staphylococcus, which was considered a contaminant.

Over the past 6 years, there were 1164 SICU patients who developed 2260 positive cultures (346 blood, 1,685 respiratory, 229 urine). The average age of patients was 43 +/- 19 years, and their average Acute Physiology and Chronic Health Evaluation II score was 22 +/- 12. Of the 1164 patients, 76% were male, and 64% suffered trauma injuries. Although there was no difference in the rate of positive blood cultures caused by Gram-positive (GP) or Gram-negative (GN) organisms in the past and present groups (P = .32), GPs became more common in the present group for both respiratory (P < .0001) and urine (P = .004) cultures. In both blood and respiratory cultures, oxacillin-resistant Staphylococcus aureus was a more common GP pathogen (22% vs 7%, P = .004 and 20% vs 11%, P = .004) and represented a larger proportion of staphylococcal species in the present group (50% vs 21%, P = .01 and 30% vs. 21%, P = .04).

Our study found that within the SICU, GP organisms play an increasing pathogenic role in critical patients. Staphylococcal species have become more common pathogens in the last 6 years, with an increase in the proportion of drug-resistant strains (oxacillin-resistant S aureus). These findings illustrate the need to keep constant surveillance on microbial trends within the SICU, especially those among drug-resistant pathogens.