Home hygiene helps tame MRSA

If your patients have not met USA300, they probably will. This superstrain of methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a global health concern among groups that gather in close proximity: professional and amateur sports teams, clubs, schools, prisons, and families.

"I think we've all seen couples and families where MRSA ping-pongs back and forth and seems impossible to eradicate," said Mark Peluso, M.D., head team physician for Middlebury College, Middlebury, Vt. "The prevention principles are the same in any group, whether you're talking sports teams or families." Middlebury's athletic department had a MRSA outbreak several years ago that was traced to an unlicensed tattoo artist, he told the American Academy of Family Physicians Annual Scientific Sessions meeting in Chicago.

"Prevention works," Peluso said. "We have had only two MRSA cases in the past three years after we instituted prevention measures." Prevention is not complicated, he added. MRSA is typically spread by contact and surface contamination.

An ounce of prevention

Simple household measures such as frequent hand-washing or use of alcohol-based hand cleansers, frequent cleaning of shared surfaces, and use of separate towels or other personal items are key. Prompt treatment of scrapes, cuts, and other wounds is also essential.

Healthcare providers have been wary of community-acquired MRSA for years, Peluso said. The first report of what would be identified as USA300 came from the United Kingdom in 1998. Five members of a rugby team contracted non-healing abscesses. Genetic analysis showed MRSA, but it was a new strain that was both highly virulent and highly resistant to treatment.

The same strain was identified in U.S. college football players in 2000 and 2002. In 2003, the same bug infected high school wrestlers from different teams who had not wrestled each other. Then USA3000 hit a private fencing club.

In August 2003, the Centers for Disease Control & Prevention warned of the new strain in Morbidity and Mortality Weekly Report. USA300 made headlines in 2005 when the New England Journal of Medicine published a report on an outbreak among St. Louis Rams football players.

There is no empiric treatment for USA300, Peluso continued. Infections must be cultured and tested. "You have to know what will kill your specific bug," he said. "Empiric therapy won't work and will add to existing resistance problems."

Fluoroquinolones are not recommended due to widespread resistance, he continued. Trimethoprim-sulfamethoxazole, doxycycline, clindamycin, and linezolid (Zyvox, Pfizer) are likely candidates, depending on local susceptibility patterns. So is rifampin in combination with other agents. More resistant infections may require intravenous treatment with vancomycin, clindamycin, daptomycin (Cubicin, Cubist), tigecycline (Tygacil, Wyeth), or linezolid.

Drug resistance

How long those agents will continue to be effective is an open question. Drug resistance has been growing at least since the 1950s, warned Thomas Kintanar, M.D., a private-practice physician in Fort Wayne, Ind.

"We have had antibiotic overuse guidelines for more than 20 years," he said, "and we are still seeing a great increase in infectious disease deaths due to resistant organisms. In 1998, CDC reported that one-third of antibiotic use was inappropriate. The issue may well have escalated."

Resistant strains of Staph aureus, Enterococcus, and other organisms are also behind the growing incidence of necrotizing fasciitis, scarring, and other permanent injuries associated with infection.

Inappropriate antibiotic use is part of the problem. Most upper respiratory infections are viral in nature, Kintanar noted, and should never be treated with antibiotics. But most patients demand antibiotics. And so do parents of children with bronchitis, sinusitis, and other common infections. Physicians too often find it easier to prescribe than to educate about the futility of using antibiotics against viruses and the growing calamity of drug resistance, he added.

There is also a lack of new antimicrobials. Some of the most recently approved agents are already losing efficacy due to resistance. Linezolid was widely overused after approval in 2000 and is not widely effective, Kintanar said. Cefditoren pivoxil (Spectracef, Cornerstone), like other third-generation cephalosporins, is only occasionally useful.

Ertapenem (Invanz, Merck), the newest carbapenem, is notable only for its once-daily dosing. Cefepime (Maxipime, Bristol-Myers Squibb), a fourth-generation cephalosporin, is used almost exclusively in the hospital setting.

Daptomycin (Cubicin, Cubist), the first cyclic lipopeptide antimicrobial, is still widely effective, Kintanar said. But it is infused over 30 minutes and is seldom used in the community.

"There are more products in the pipeline, but nothing that is near approval," he noted. "Daptomycin is probably the last line of defense we have right now."