No magic bullet for MRSA SSIs

February 15, 2010

Most agents used for presurgical prophylaxis are not effective against MRSA. To reduce MRSA-related surgical site infections,says one expert, you need to prevent all SSIs.

Key Points

Reducing the incidence of surgical site infections (SSIs) caused by methicillin-resistant Staphylococcus aureus (MRSA) is good medicine and good business. Data published in 2009 show that preventing a single MRSA-caused SSI can save a hospital more than $60,000.

"These infections cause significant adverse patient outcomes and increased costs," said lead author Deverick Anderson, MD, MPH, co-director of the Duke Infection Control Outreach Network at Duke University Medical Center, Durham, North Carolina. "MRSA is far and away the No. 1 cause of SSIs. We see it in all types of hospitals, from small rural institutions to large teaching institutions."

A multi-center study published in PLoS One in December 2009 found that MRSA is responsible for a mean of 28 days of hospitalization compared to five days for other SSIs. The additional hospitalization drives the mean cost of treatment from $50,463 per case to $112,144. That is nearly $62,000 more for every case of MRSA SSI.

Well-known risk factors for SSIs include patient age, diabetes, obesity, smoking, and immunosuppression. But the biggest single risk for MRSA SSIs is the need for assistance with three or more activities of daily living (ADLs). Patients who need help with at least three ADLs such as eating, bathing, dressing, toileting, and moving have an odds ratio (OR) of 3.97 for developing MRSA SSI.

Other independent risk factors for MRSA SSIs include Medicaid insurance (OR 3.31), wound classification of >2 (OR 2.91), duration of surgery above the 75th percentile (OR 1.98), and obesity (OR 1.86). The need for assistance with three or more ADLs and longer duration of surgery are also independent risk factors for MRSA SSI in comparison with SSI connected with methicillin-susceptible S. aureus.

One problem, Dr. Anderson said, is that the vast majority of agents used for presurgical prophylaxis are not effective against MRSA. Patients colonized with MRSA are two to nine times more likely to develop an SSI than patients colonized with methicillin-susceptible S. aureus, but data show that decolonization of patients before surgery has no effect of SSI rates.

Vancomycin (Vancocin, Lilly) can be used for presurgical prophylaxis against MRSA, but it is not a cure-all. Vancomycin is not effective against gram-negative organisms, Dr. Anderson said. It has a narrower spectrum of activity against gram-positive organisms than the beta lactam agents usually used for presurgical prophylaxis. Vancomycin infusion takes more than an hour and widespread use raises significant concerns about vancomycin resistance.

That does not meant that vancomycin is not useful in specific circumstances. Duke used a combination of vancomycin and rifampin (Rifidin, Sanofi-Aventis) along with cefuroxime (Ceftin, GlaxoSmithKline) for antibiotic prophylaxis to combat an outbreak of MRSA SSI in 2000. In addition to enhanced presurgical prophylaxis for high-risk patients, Duke instituted more aggressive glucose control and increased compliance with preoperative antiseptic showers, using chlorhexidine gluconate for all surgical patients.

A before-and-after study showed significant decreases in all SSIs as well as MRSA SSIs. Study data showed that SSI and MRSA SSI rates plummeted with the new protocols and remained low for six years. Dr. Anderson said the rates have continued at the same low level into 2010.

"There are no well-proven methods to reduce MRSA SSIs," he said. "You have to target SSIs before you can target MRSA SSIs. But there may be specific patients who could benefit from specific measures. You need to know your own epidemiology before you act."