Decreased Incidence of Methicillin-Resistant Staphylococcus aureus Bacteremia in Intensive Care Units: a 10-Year Clinical, Microbiological, and Genotypic Analysis in a Tertiary Hospital

Abstract

Background: There are limited long-term data on the trends in incidence and characteristics of MRSA bacteremia (MRSAB) in intensive care units (ICUs) in which infection control measures have been adopted. Methods: We evaluated the trend of incidence and changes in characteristics of MRSA bacteremia in ICUs using prospective cohort data at a tertiary-care hospital over 10 years. ICU-acquired bacteremia was defined as S. aureus bacteremia (SAB) that occurred 48h or more after ICU admission. MRSA isolates were collected and subjected to microbiological and genotypic analyses. Results: A total of 529 SAB episodes were identified among 367,175 ICU patients. Of these episodes, 288 (54.4%) were ICU-acquired, of which 238 (82.6%) were MRSAB. The incidence density of ICU-acquired MRSAB decreased from 1.32 per 1000 patient-days to 0.19 per 1000 patient-days (a decrease of 20% annually, P < 0.001 for trend), whereas that of non-ICU-acquired MRSAB fluctuated and did not decrease significantly. The decline in ICU-acquired MRSAB was due to lower catheter-related infection and less pneumonia. Rates of persistent bacteremia and 12-week mortality also fell significantly. A total of 183 isolates were collected from 238 ICU-acquired MRSAB. There were no significant changes in the geometric means of vancomycin MICs, vancomycin heteroresistance, and the sequence types of MRSA isolates over time. Chlorhexidine MICs decreased (P < 0.001 for trend) in association with a decline in frequency of the qacA/B gene that was related to reductions in specific spa types. Conclusions: The incidence of MRSAB in ICUs has decreased dramatically over time, but most of the microbiological and genotypic characteristics of MRSA isolates have not changed.