BOSTON – Preoperative nasal carriage of methicillin-resistant Staphylococcus aureus increases the risk of postsurgical infection despite prophylaxis with vancomycin, based on a study of more than 4,000 patients.
The findings confirm the utility of preoperative screening for MRSA nasal carriage and suggest that patients who test positive may benefit from additional interventions to prevent postoperative infections, Dr. Kalpana Gupta reported at the conference.
To assess the relationship between preoperative nasal MRSA carriage, prophylactic antibiotics, and postoperative surgical infections and cultures, Dr. Gupta of the VA Boston Healthcare System and her colleagues retrospectively studied all patients in the nine-campus system’s veteran population who had a clean or clean-contaminated surgical procedure between Jan. 1, 2008, and Dec. 31, 2009, and who had undergone MRSA screening within 31 days of surgery.
The data extracted from the VA electronic health records included:
• MRSA nasal status within 31 days before and after surgery.
• MRSA nasal status and culture status in the year before surgery.
• Date, type, and American Society of Anesthesiologists (ASA) class of surgery.
• Duration of procedure.
• Surgical skin preparation used.
• Postoperative outcomes, including MRSA, methicillin-sensitive S. aureus, and other organisms, within 1 year after surgery.
• National Surgical Quality Improvement Program data with risk factors of interest, comorbidities, and postoperative complications.
• Perioperative prophylaxis agents, including vancomycin, cefazolin, and other antibiotics.
Of the 4,238 surgical patients who had undergone a nasal swab in the month before surgery, 279 were MRSA nasal positive and 3,959 were MRSA nasal negative. Postoperatively, 12% of the nasal-positive patients had a MRSA-positive clinical culture within 31 days, compared with 0.75% of the nasal-negative patients – a difference that remained significant when stratified by surgery type and ASA class, Dr. Gupta reported. Similarly, the nasal-positive patients were significantly more likely to have any type of MRSA infection as well as a MRSA surgical infection in the month after surgery, she said at the conference sponsored by the American Society for Microbiology.
Among all of the patients, neither vancomycin nor cefazolin prophylaxis protected against positive MRSA cultures or infections, nor did the use of chlorhexidine scrub in the operating room, Dr. Gupta noted, stating “we already take a lot of preventive measures, but those measures may not be enough.”
The findings highlight the need for decolonization strategies in MRSA-colonized patients, particularly those undergoing higher-risk procedures, Dr. Gupta stated. Given the possibility that decolonization efforts could lead to the development of resistance in MRSA, the investigators plan to conduct further research using MRSA isolates to study how resistance develops, she said.
The findings of the study are limited by the low overall infection rate, according to Dr. Gupta, who noted that higher numbers would have provided more insight into the efficacy of prophylactic strategies.