Dec. 3, 2007

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Waging Battle on Resistant Bugs

Graham Ramsay Erica Siguer Shenoy

I’ve just received the “FYI” text page from admitting informing me of the name and medical-record number of the first patient I’ll be admitting tonight. I log into the nearest computer and begin cruising the medical record, looking through previous electronic notes and discharge summaries, laboratory studies, and radiology reports, when I notice a red P highlighting the top right of the screen. It’s the P for precautions, which means that this patient has been found to harbor one of a variety of resistant bacteria, in this case, methicillin-resistant Staphylococcus aureus, or MRSA.

No doubt many readers of this publication are familiar with MRSA, and chances are that a large proportion of the lay public is aware as well, given the media attention to a study published this past October in The Journal of the American Medical Association. “A Nasty Bug Breaks Out” was the headline of an article in U.S. News and World Report, and in the Boston Globe, “Infection Spurs Wrentham School Clean Up” featured data from the study’s findings and told the story of an elementary student whose diagnosis with MRSA infection spurred the school to have its buildings professionally sanitized using bleach and water. MRSA describes a strain of Staph aureus that is resistant to methicillin, as well as oxacillin, penicillin, and amoxicillin, all commonly used antibiotics.

Checking Infection

My patient, a 56-year-old lady with end-stage renal disease secondary to diabetes, was admitted because she developed fever and chills while at dialysis. The concern is for a bloodstream infection. Her past medical history is lengthy, but most significant is her recent prolonged hospital course for MRSA bacteremia, which was complicated by osteomyelitis in one of her vertebrae. When bacteria such as MRSA enter the bloodstream, they can travel anywhere and everywhere, and the bone presents a particular problem, requiring lengthy courses of the powerhouse IV antibiotic, vancomycin, which may not eradicate the infection.

In my patient’s case, I wonder if she was indeed bacteremic at dialysis. Had she been re-infected by some source, perhaps through her dialysis catheter? Or was her bone infection (which resulted in the complete collapse of that vertebra) not eradicated so she is seeding her bloodstream from this reservoir? This last possibility is ominous because it would mean that despite receiving the first-line drug for MRSA, she has not cleared the infection. Has her MRSA become a VISA (vancomycin-intermediate Staphylococcus aureus) or a VRSA (vancomycin-resistant Staphylococcus aureus)? Only the blood culture data will tell.

The Scope of Resistance

MRSA can be acquired in hospital settings, where it accounts for about 65 percent of all Staph aureus infections in U.S. intensive care units, or in the community. In the JAMA study, by researchers at the Centers for Disease Control and Prevention (CDC), the Active Bacterial Core surveillance (ABCs) system, part of the Emerging Infections Program Network at the CDC, was used to find cases of invasive MRSA infections in nine areas across the country. The majority of cases were health care associated, though among these, more than half were community-onset MRSA. The study identified those risk factors associated with acquiring MRSA, including a history of hospitalization, history of surgery, residing in a long-term care facility, or previous MRSA infection or colonization.

Based on the data from the nine sites, the study authors were able to estimate the national incidence of invasive MRSA infections in 2005 to be 94,360. They believe that these infections resulted in approximately 18,650 deaths. The incidence of invasive MRSA was found to vary geographically and by race, even controlling for underlying chronic illness. The authors note, however, that the association between race and invasive infection may be confounded by socioeconomic status. While the study has its limitations (including that the number of deaths was based on in-hospital death rates and MRSA may not have been the proximate cause), the findings nonetheless provide a comprehensive view of the extent of MRSA across the country.

A variety of strategies have been employed to decrease the incidence of MRSA infection. In hospitals across the country, infection control programs have instituted policies that require isolation of patients with MRSA, and health professionals in contact with the patient must use gowns and gloves and specific hand-disinfecting procedures. With capacity at its limit at hospitals like Massachusetts General, patients with MRSA are often put into the same double-occupancy room. These policies can have a major impact on the transmission of MRSA, as well as other resistant hospital-acquired organisms.

Fortunately, as of this writing, my patient’s blood cultures remain negative. The infectious disease specialists will soon weigh in on what to do next, as will the orthopedic spine service, which may have to intervene surgically.

—Erica Seiguer Shenoy, MD–PhD ’07, is an intern in internal medicine at Massachusetts General Hospital.

Related Links
Klevens et al., Invasive Methicillin-Resistant Staphylococcus aureus Infections in the United States. JAMA 2007; 298:1763-1771.
http://jama.ama-assn.org/cgi/content/full/298/15/1763

Management of MRSA in Health Care Settings (CDC)
http://www.cdc.gov/ncidod/dhqp/pdf/ar/mdroGuideline2006.pdf

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Copyright 2007 by the President and Fellows of Harvard College