Antibiotic resistance is a complication of treating patients in the intensive care unit (ICU) who have contracted healthcare-acquired infections (HAIs), but according to Marie-Laurence Lambert, MD, of the of the Scientific Institute of Public Health in Brussels, and colleagues, this resistance does not increase mortality. The research was published online in Lancet Infectious Diseases.

In their study, Lambert, et al. (2010) sought to assess excess mortality and length of stay in intensive-care units from bloodstream infections and pneumonia. The researchers analysed data collected prospectively from ICUs that reported according to the European standard protocol for surveillance of HAIs, focusing on the most frequent causative microorganisms. Resistance was defined as resistance to ceftazidime (Acinetobacter baumannii or Pseudomonas aeruginosa), third-generation cephalosporins (Escherichia coli), and oxacillin (Staphylococcus aureus). The researchers defined 20 different exposures according to infection site, microorganism and resistance status. For every exposure, the researchers compared outcomes between patients exposed and unexposed by use of time-dependent regression modelling, and adjusted results for patients' characteristics and time-dependency of the exposure.

The researchers report that they obtained data for 119,699 patients who were admitted for more than two days to 537 ICUs in 10 countries between Jan 1, 2005, and Dec 31, 2008. Excess risk of death (hazard ratio) for pneumonia in the fully adjusted model ranged from 1Â·7 (95% CI 1Â·41Â·9) for drug-sensitive S aureus to 3Â·5 (2Â·94Â·2) for drug-resistant P aeruginosa. For bloodstream infections, the excess risk ranged from 2Â·1 (1Â·62Â·6) for drug-sensitive S aureus to 4Â·0 (2Â·75Â·8) for drug-resistant P aeruginosa. Risk of death associated with antimicrobial resistance (ie, additional risk of death to that of the infection) was 1Â·2 (1Â·11Â·4) for pneumonia and 1Â·2 (0Â·91Â·5) for bloodstream infections for a combination of all four microorganisms, and was highest for S aureus (pneumonia 1Â·3 [1Â·01Â·6], bloodstream infections 1Â·6 [1Â·12Â·3]). Antimicrobial resistance did not significantly increase length of stay; the hazard ratio for discharge, dead or alive, for sensitive microorganisms compared with resistant microorganisms (all four combined) was 1Â·05 (0Â·971Â·13) for pneumonia and 1Â·02 (0Â·981Â·17) for bloodstream infections. P aeruginosa had the highest burden of HAIs because of its high prevalence and pathogenicity of both its drug-sensitive and drug-resistant strains.

The researchers conclude that healthcare-acquired bloodstream infections and pneumonia greatly increase mortality and pneumonia increases length of stay in intensive-care units, but that the additional effect of the most common antimicrobial resistance patterns is comparatively low.

Reference: Lambert ML, Suetens C, Savey A, Palomar M, Hiesmayr M, Morales I, Agodi A, Frank U, Mertens K, Schumacher M and Wolkewitz M. Clinical outcomes of health-care-associated infections and antimicrobial resistance in patients admitted to European intensive-care units: a cohort study. The Lancet Infectious Diseases. Dec. 1, 2010.