MRSA: predictor of outcome in critically ill patients

Methicillin resistant Staphylococcus aureus (MRSA) infectionin critically ill patients is associated with considerable morbidity,mortality and cost.^{1 2} In 1994, we studied 29 MRSA positivepatients admitted to the intensive care unit (ICU). Althoughthe size of population studied was too small to be conclusive,there was a suggestion that MRSA did not have a significantimpact on overall mortality (unpublished observation), however,there was an increase in average length of stay. In this retrospective study, microbiology records identifiedMRSA infected/colonised patients admitted to ICU over 36 months(1996–1998). Patient demographics, site of isolation andhospital mortality were recorded. Isolation of MRSA from blood,sterile sites or endotracheal secretions was considered to bea surrogate marker of serious infection. In those patients withMRSA isolated in multiple sites, the most likely site for seriousinfection was selected. One hundred and sixty seven patients were found to be infected/colonizedwith MRSA and of these 59 patients had positive blood or sputumcultures. Hospital mortality of MRSA positive patients was 50.9%compared to 33.8% overall hospital mortality of all ICU patients.Standardized incidence ratio for death was 1.51 (95% confidenceinterval 1.20–1.86) for patients with MRSA. As expectedthe number of deaths rises with age (60 yr was 34.8%, 61–75yr 52.6%, >75 yr 64.4%. Odds ratio 2.74 (95% confidence interval1.09–6.93) for >75 compared with 60 yr old). Diagnosis of MRSA from blood and sputum (group A) had a mortalityof 44.1%, compared to 51.3% in those with MRSA from screeningsites (group B) (P=0.403). Whilst mortality increases with agefor both groups, it rises faster in patients with MRSA in groupB (Table 7). There was no difference in mortality between groups. The poorassociation between mortality and positive blood or sputum culturescorroborates our previous observation that detection of MRSAis more likely to be an indicator of poor prognosis rather thanthe cause of fatal infection.