Predictive factors of meticillin resistance among patients with Staphylococcus aureus bloodstream infections at hospital admission

Summary

Meticillin-resistant Staphylococcus aureus (MRSA) is prevalent throughout the healthcare system in Spain, particularly in long-term care facilities (LTCF) and the incidence of MRSA bloodstream infection (MRSA-BSI) at hospital admission is increasing. This study aimed to determine factors that predict meticillin resistance among patients who require hospitalization for S. aureus BSI. We performed a case–control study comparing patients with S. aureus at hospital admission from January 1991 to December 2003. Case patients with MRSA-BSI at hospital admission (N = 50) were compared with control patients with meticillin-susceptible S. aureus bloodstream infection (MSSA-BSI) at hospital admission (N = 98). The incidence of MRSA-BSI at hospital admission increased significantly from 0.08 cases/1000 hospital admissions in 1991 to 0.37 cases in 2003 (P < 0.001). Univariate analysis comparing patients with MRSA- and MSSA-BSI found a significant association between meticillin resistance and age >60 years, female sex, prior MRSA isolation and healthcare-related BSI. No differences were found in underlying conditions such as diabetes, haemodialysis, immunosuppression, source of infection or mortality between the two groups. Multivariate analyses identified prior MRSA isolation [odds ratio (OR): 41; 95% confidence interval (CI): 4–350] and admission from long-term care facilities (OR: 37; 95% CI: 4.5–316) as independent risk factors for MRSA-BSI.

Introduction

In Spain, the introduction and successful dissemination of the Iberian clone in acute care hospitals was first reported in 1990 and produced a widespread epidemic of MRSA infection in hospitalized patients.1, 2 Initially, MRSA was considered a strictly nosocomial pathogen. Strains then moved from large teaching institutions to small community hospitals and long-term care facilities, in which they became endemic.3, 4, 5, 6

The persistence of high MRSA prevalence in Spanish hospitals, despite control measures, has been ascribed to a lack of strategies to limit spread of MRSA from hospitals to the community. In these settings, widespread dissemination of MRSA has been reported among residents and silent carriage may persist for several years.7, 8 Patients who become ill may have unrecognized carriage of MRSA at the time of hospital admission, resulting in delay in use of appropriate antimicrobial treatment and a failure to implement effective MRSA infection control measures.⁹S. aureus is a serious and common cause of bacteraemia, both in hospital and outside. Though meticillin-resistant S. aureus bloodstream infections (MRSA-BSI) represent an increasing problem in emergency departments, few studies have addressed the issue.3, 4, 5, 6, 10, 11, 12

The aims of this study were to determine frequency and trends of MRSA-BSI at hospital admission and to describe predictors of meticillin resistance among patients who require hospitalization for S. aureus bloodstream infection.