Transmission of MRSA Traced to Breast Milk


WASHINGTON — Methicillin-resistant Staphylococcus aureus has been transmitted via breast milk, Dawn Terashita Gastelum, M.D., reported in a poster presentation at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy.

The two reported cases, which resulted in MRSA outbreaks in neonatal intensive care units at two Los Angeles hospitals, suggest that hospital NICUs should consider screening mothers and family members for skin lesions at the time of delivery and obtaining breast milk cultures before infant feedings, said Dr. Terashita Gastelum of the Los Angeles County Department of Health Services.

The first case was in a premature (1,180 g at birth) quadruplet born to an Algerian mother who developed mastitis the day after delivery and was treated with dicloxacillin. Her breast milk was collected 3 days later and fed to the quadruplets. Twelve days after that, the baby girl died of MRSA sepsis.

The bacterium subsequently was found in nasopharyngeal cultures of the mother and her three surviving infants, another infant in the NICU, and the mother's frozen postpartum breast milk samples. Molecular fingerprinting was identical for the four infants and the breast milk, but the mother's nasopharyngeal isolate was different.

“Since the mother was actually colonized by a different strain, it is unlikely that the infants obtained the MRSA during birth or through skin-to-skin contact with the mother. The breast milk is the only known source,” Dr. Terashita Gastelum told this newspaper.

And, though it is possible to be colonized with two different strains of MRSA, it's rare. On the other hand, “it is easy to imagine that the macerated skin of the nipple on a postpartum woman is more susceptible to infection from any organism,” she said at the conference, sponsored by the American Society for Microbiology.

The second case was an 1,199-g male infant born to an African American mother, who was fed her breast milk the day of birth and developed MRSA sepsis 8 days later. This mother had no sign of mastitis, but MRSA was cultured from her breast milk collected on the day of delivery. Four other infants from the NICU were also positive: two colonized and two infected. Isolates from the breast milk and the five cases were identical.

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