MRSA Infections May Lose Antibiotic Resistance

A new study has found that methicillin-resistant Staphylococcus aureus (MRSA) skin infections reverted to methicillin-susceptible status in 30% of cases, under certain situations.

Researchers at the Oregon Health and Science University (OHSU; Portland, USA) conducted a study that evolved from anecdotal observations of apparent conversion from MRSA to methicillin-susceptible Staphylococcus aureus (MSSA) status during flares in patients with atopic dermatitis. To examine the issue more closely, the researchers reviewed 1,496 culture records in the microbiology database and identified all patients who had MRSA-positive skin and soft-tissue infection. The researchers then examined patients who subsequently had a second culture test for a skin and soft-tissue infection on a different area of the body, or in the same area but at least one month after the first culture; the search identified 219 such patients.

The results of second culture tests showed that about 30% of the patients reverted to MSSA. The researchers then compared patients who did not revert to MSSA with those who did. Examination of a dozen factors known to be associated with persistent MRSA yielded a significant association only for use of an invasive device. Factors that did not differ between patients who reverted and those who did not included treatment with immunosuppressive drugs, antibiotics within a week of positive culture, previous MRSA-positive non-skin and soft-tissue infection, and intravenous (IV) drug use. The study was presented as a poster session at the Society for Investigative Dermatology annual meeting, held during May 2012 in Phoenix (AZ, USA).

“MRSA skin and soft-tissue infections can convert to MSSA in subsequent infections, making it important for practitioners to reculture infections when possible,” said lead author and study presenter Anisha Patel, MD. “This can keep physicians from unnecessarily limiting antibiotic choices and possibly extending resistance.”

The researchers suggested that a database of dermatologist-diagnosed primary cutaneous disorders and the infectious history of those patients would be useful in characterizing reversal rates to MSSA, and help classify who is at highest risk for continued MRSA skin and soft-tissue infections, and how this affects primary skin disease.

Related Links:
Oregon Health and Science University