The bacteria Staphylococcus aureus (staph) causes a skin infection that appears red, swollen, and painful, resembling a pimple or a boil. Such infections often resolve with cleaning and drainage and, in some cases, a course of antibiotics. Fortunately, many staph infections will never require antibiotic treatment.

Certain strains of staph, though, don’t go away when treated with the beta-lactam family of antibiotics that is often prescribed; this family includes methicillin, penicillin, and amoxicillin. Called methicillin-resistant Staphylococcus aureus (MRSA), this bacteria was once confined to hospital and nursing home populations, but is now showing up in otherwise healthy adults (where it is then called community-associated MRSA ). Worse, some of the community-associated MRSA strains contain toxins that may lead to more serious infection than is commonly seen with other staphylococcal infections originating outside the hospital.

Community-associated MRSA has been a particular problem in populations having close physical contact, such as sports teams, prison inmates, injection drug users, and military recruits. A recent outbreak has been blamed on unsanitary tattooing practices, but in most cases the source and exact mode of transmission are unclear. The frequent occurrence in teams suggests that contact with contaminated equipment or surfaces, or close physical contact such as during football scrimmages, may play a role.

Hoping to measure the rise of MRSA, researchers analyzed samples from the skin or soft tissue infections of 422 adults who visited 11 emergency rooms. Their findings, in the August 17, 2006 New England Journal of Medicine, reveal that MRSA was the number one cause of skin or soft tissue infections at 10 of the 11 sites and accounted for 59% of all infections in the study.

About the Study

During August 2004, UCLA Medical Center researchers collected samples from the skin and soft tissue infections of 422 adults seen in emergency rooms in 11 US cities. Testing was done to determine the bacterial cause of each infection, as well as the vulnerability or resistance of each bacterium to various antibiotics.

MRSA caused 59% of skin and soft tissue infections in this sample of otherwise healthy adults, and was the number one culprit at 10 of the 11 sites. Further analysis showed that 97% of MRSA samples were the specific genetic strain of community-associated MRSA. Although resistant to treatment with methicillin, the MRSA samples did respond to other antibiotics—100% responded to rifampin or trimethoprim-sulfamethoxazole, 95% to clindamycin, and 92% to tetracycline. Most MRSA is resistant to cephalosporins, another common group of antibiotics traditionally used to treat staph infections.

While rifampin and other antibiotics killed MRSA in the laboratory, these antibiotics require further study in patients to determine their clinical usefulness. The majority of patients who received antibiotics in this study had MRSA that were resistant to the antibiotics. Treating doctors seemed to be unaware of how prevalent this organism was in their emergency rooms. Fortunately, patients given the “wrong” antibiotic fared just as well as those whose doctors guessed right and prescribed a drug effective against MRSA. This finding likely emphasizes that many persons with skin infections (especially boils) don’t need antibiotics to heal. Of more importance perhaps, 34% of persons with MRSA had taken antibiotics in the preceding month.

Using antibiotics increases an individual’s risk for becoming infected with organisms that are drug-resistant. This study emphasizes that even in distinguished emergency rooms, antibiotics may not always be administered wisely (wrong drugs for patients with high likelihood of MRSA, use of antibiotics when simple opening of an abscess would likely cure the patient). Prior antibiotic use, whether indicated or not, was associated with becoming infected with MRSA.

How Does This Affect You?

This study highlights the startling rise in the prevalence of community-associated MRSA infections across the US. The authors primarily reported overall prevalence of MRSA among patients with skin infections, but when they looked just at staphylococci isolated from wounds, 78% were resistant to methicillin. While many cases are mild, MRSA can cause ]]>pneumonia]]> or bloodstream infections in both adults and children. Such infections generally require hospitalization and lead to significant disability or even death. Due to the resistance of certain staph strains to antibiotics, the study authors encourage doctors to culture all such infections to determine the most effective drug therapy.

It is important to recognize that patients visiting inner city emergency rooms (the subjects of this study) are not necessarily representative of Americans as a whole. MRSA may be more common among poor people (homelessness, recent incarceration, and IV drug use were not uncommon in the population studied), but it has been reported in all socioeconomic classes.

To avoid an MRSA skin or soft tissue infection, follow these guidelines from the Centers for Disease Control and Prevention:

  • Wash hands often with soap and water or use alcohol-based hand sanitizer.
  • Wash hands after contact with pets. Some domestic animals (including dogs, cats, and horses) carry MRSA and may be responsible for transmitting it to humans.
  • Keep cuts and scrapes clean and covered with a bandage until healed.
  • Do not share personal items such as towels, wash cloths, or razors.
  • Avoid contact with other people’s wounds or bandages.
  • At the health club or during athletic participation:
    • Use a physical barrier, such as a towel, between your skin and shared equipment.
    • Wipe equipment surfaces before and after use.

    If you notice signs of an infection—redness, warmth, swelling, discharge—contact your doctor. Seek care rapidly if in addition you have fever, chills, or other symptoms suggesting the infection is not just located on your skin.

    Most skin infections should be treated by frequent soaking with hot (not scalding) water. To prevent spreading your infection to other people, keep the area clean and covered; wash your hands thoroughly after changing the bandage; wash and dry bedding, towels, and clothing that may have come in contact with the wound; and–if diagnosed with MRSA–tell any healthcare provider who treats you that you have a resistant staph infection.

    Be sure to confirm with your doctor that, if you request or are prescribed an antibiotic, it is necessary for your recovery. As this study demonstrates yet again, many patients still receive antibiotics for infections that will almost certainly heal well without them. And if you do have a skin infection that requires drug treatment, be sure you and your doctor weigh the possibilities of MRSA before selecting an antibiotic.