A Heads Up for MRSA Mastitis

Notes from Dr. Hale

We are all hearing more and more about the new epidemic of Methicillin-Resistant Staph Aureus (MRSA). While the rate in the general public is still low, it is rising and it seems especially so in pediatric age patients where a higher prevalence seems to occur in settings that enable close contact between individuals, such as day-care centers.

S aureus can colonize the nasopharynx, perineum, or skin. The most common way to screen for colonization is culture of specimens from the nasopharynx. Although most colonized individuals remain asymptomatic, small disruptions of the skin can lead to local infections. One-third of the general population and up to 50% of those with chronic medical conditions (renal failure, diabetes, etc) can be chronically colonized with S aureus. In healthy persons, the rates of MRSA colonization were in the past low, but have been steadily increasing. In children, the colonization rate ranges from 0.8 to 3.0% but these too seem to be increasing. A recent study in Texas children reported a 14-fold increase in cases in 1999-2001.

More importantly, our hospitals are now reporting high rates of MRSA. My own hospital reports 54% of the strains of S aureus, are methicillin-resistant.

Recent reports of MRSA mastitis have been increasing, including infections in premature infants from MRSA infected milk. Numerous clinicians in the field report that they commonly see it in their practices. Many such clinicians are now culturing milk samples prior to prescribing antibiotics, so that if the antibiotic fails, they’ll have a culture to guide their subsequent therapy. This is probably wise.

But it is still important to remember, that the most likely cause of mastitis in breastfeeding mothers is still the old penicillin-resistant S. aureus, not MRSA. Because penicillin-resistant mastitis still commonly occurs in the breastfeeding population, and is still well-treated with dicloxacillin, cephalexin, trimethoprim-sulfamethoxazole, or even macrolide antibiotics, clinicians are advised that in most instances these older antibiotics are still the best “first” choices.

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