MRSA by the Numbers

By now, almost everyone has heard of MRSA (methicillin-resistant Staphylococcus aureus)—variants of the ubiquitous “staph” bacteria that are resistant to penicillin and related antibiotics—the original “wonder drugs” that transformed the treatment of infectious diseases in the mid-20th century.  Methicillin is the antibiotic named to signify resistance to the class that includes penicillins (even though bacteria are not routinely tested against it). Methicillin, no longer used because of its toxicity, was developed in 1959, a decade after bacteria resistant to pencillin arose (which occurred a mere four years after penicillin went into mass production). This is a lesson we still must heed today—that resistance is an inevitable natural phenomenon, bound to occur against every antibiotic the more it is used.

MRSA news stories tend to focus on healthy young victims who’ve picked up the bacteria on the football field, in school, or somewhere else in the course of daily living, and end up with an overwhelming infection that puts them into the intensive-care unit. MRSA may kill through infections of the lung, blood, or tissue (it’s one of the “flesh-eating bacteria”). What has happened to these victims is shocking and tragic, of course, but their cases represent just a small part of the larger MRSA problem. Sadly, the more numerous deaths of elderly hospital patients with serious medical problems are not exactly front page material.

Both MRSA and common staph are typically harmless on the surface: they can “colonize” the skin or the nasal passages without causing any health problems.  When they enter broken skin through a cut or sore, however, they “infect” the surrounding tissue and proliferate in boils, blisters, or pimples. Often these skin and soft tissue infections can just be cleaned out and left to heal.  But when bacteria invade the bloodstream, causing blood infections called septicemia or bacteremia, or the lungs, causing pneumonia, the situation becomes much more serious, and quickly.  When these staph infections are MRSA, they take longer to cure, about doubling the time spent in the hospital, and also doubling the hospital bill.  

Septicemia and pneumonia are almost exclusively acquired in hospitals or other healthcare settings, where staph bacteria are ubiquitous if no special infection control measures, such as testing new patients and isolating those who are colonized, are in force.  Bacteria can enter patients’ internal organs during surgery, around catheters used to infuse intravenous drugs and fluids, and around urinary catheters.  The result can be deadly MRSA infections—especially in patients who are already weakened by illness or old age. Ironically, the infection “vectors” in hospitals are often healthcare workers who become colonized and then spread the bugs around.

National and local publicity has raised public consciousness about MRSA, although it doesn’t inform us about the extent of the problem. RFF researchers Eili Klein, David Smith, and Ramanan Laxminarayan analyzed data from the past few years to answer that question, as part of Extending the Cure, an ongoing research project on antibiotic resistance. What their analysis tells us is that, unlike some health scare stories that represent only a small risk, this one is growing and worth worrying about. The fact that the development of new antibiotics is at an all-time low could turn this into a full-scale disaster—a return to the pre-antibiotic era, when ordinary infections were deadly.

Here are some basic statistics from Extending the Cure: MRSA infections treated in hospitals more than doubled nationwide between 1999 and 2005, from an estimated 127,000 to 278,000.  MRSA also represents a growing proportion of staph infections seen in hospitals—growing from 40 percent in 1999 to 60 percent in 2005.  The numbers themselves are difficult to verify and are the subject of controversy. Using a different data source and other methods, other researchers estimated that the national prevalence rate of MRSA among hospital patients in 2006 was 5 to 8 times as high as what Klein and colleagues reported for 2005. Putting these differences in perspective, it’s worth remembering the MRSA phenomenon is relatively recent:  in the late 1980s, resistant staph bacteria accounted for perhaps 2 percent of infections.  

Counting infections in hospitals is tricky, but the question of how many people die from MRSA is even more difficult and involves judgment calls. Many people who die entered the hospital because they had a life-threatening condition and were already advanced in age. In this context, any infection is more perilous than it would be for a healthy, young person: in other words, the infirm and elderly may die in the hospital even without MRSA.

This led Klein, Smith, and Laxminarayan to create two estimates of deaths attributable to MRSA. Using stricter criteria, they estimated about 5,500 deaths per year over the seven-year period, with no suggestion of a trend up or down. Using a more inclusive definition—everyone who died and had a documented case of MRSA during their hospitalization—the estimates were higher and rose steadily. In 1999, about 11,000 such deaths occurred, and by 2005, more than 17,300. Using similar definitions and entirely different data sources, two other groups of researchers came up with very similar results for deaths in 2005: from the Centers for Disease Control and Prevention (CDC), 18,650 deaths, and from the Agency for Healthcare Research and Quality, 17,300 deaths.

Patients hospitalized with MRSA infections included both those with septicemia and pneumonia who acquired their infections during their hospital stay and those more likely to have picked up the infection in the community (skin and soft-tissue infections, mainly “non-invasive”). Septicemia cases increased 81 percent over seven years and pneumonias increased 19 percent. But the steepest increase by far was in the “community-associated” skin and soft-tissue infections, which nearly tripled between 1999 and 2005. Most deaths from MRSA still result from infections that take root in hospitals, but the community-associated MRSA burden is becoming increasingly important.

As important as it is to keep track of MRSA cases and count those who die from MRSA, it is even more important to institute preventive measures to reduce the spread of MRSA and other infections in hospitals, nursing homes, and other healthcare sites. We already know some measures that work—including testing patients (all or “high-risk” only) on hospital admission and isolating the ones who are colonized or infected, implementing “contact” precautions for hospital workers (for example, keeping stethoscopes and other equipment in patients’ rooms, promoting better hand hygiene by the staff). The other approach stems from that early lesson: antibiotics should be used to preserve health and save lives, but we should use them wisely, when they are the best course. Just knowing what works is not enough, however. The right incentives—both carrots and sticks—must be in place. That will require finding the precise mix of legislation, regulation, and economic incentives to improving infection control that will work, a hunt that cannot wait any longer.

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Views expressed are those of the author. RFF does not take institutional positions on legislative or policy questions.

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