Relative proportion of MRSA increasing in S. aureus isolates

(HealthDay)—The relative proportion of methicillin-resistant Staphylococcus aureus (MRSA) is increasing in S. aureus isolates, and methicillin-sensitive S. aureus (MSSA) is becoming increasingly resistant to antibiotics, according to a study published in the April issue of JAMA Dermatology.

Marilyn Zabielinski, M.D., from the University of Miami Miller School of Medicine, and colleagues conducted a retrospective study using observational data from skin culture isolates from a hospital outpatient dermatology clinic. Three hundred eighty-seven S. aureus isolates were analyzed from Jan. 1, 2005, through June 30, 2011, to determine whether the relative proportions of MRSA and MSSA were changing or stable.

The researchers found that the overall relative proportions of MRSA and MSSA were 35.7 and 64.3 percent, respectively. The relative proportions were 33.3 and 66.7 percent, respectively, during the final six months of the study. Compared with the period from Jan. 1, 2005, through Dec. 31, 2007, the relative proportion of MRSA was significantly higher for the period from Jan. 1, 2008, through Dec. 31, 2010 (45.3 versus 28.3 percent). The sensitivity of MRSA to ciprofloxacin increased during the study period, while MSSA became increasingly resistant to ciprofloxacin, clindamycin, gentamicin sulfate, and trimethoprim-sulfamethoxazole.

"Consistent with national data, the relative proportion of MRSA in this outpatient dermatology clinic in Miami has risen," the authors write. "In addition to the rise in proportion of MRSA in our outpatient dermatology clinic, we observed a notable trend that MSSA is becoming more resistant to many antibiotics."

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