There is nothing unusual about finding methicillin-resistant Staphylococcus aureus (MRSA) in infants undergoing neonatal intensive care. When discovered, it is often assumed that these colonizations are healthcare-acquired. However, a recent study suggests that many cases of MRSA are acquired by neonates from their mothers, transmitted vertically in the perinatal period.

In a prospective surveillance of 3707 infants admitted to an NICU over a 13-year period from 1993 to 2006, 130 (3.5%) of infants were identified to be colonized with MRSA. From 2004 to 2006, admission cultures were performed, and 1.2% of admission nasal cultures were positive for MRSA. These MRSA isolates were genotyped, revealing that they were not all healthcare-acquired as initially assumed; some were community-acquired clones. Community-acquired MRSA (CA-MRSA) first appeared in the NICU in 1998, increasing significantly between 1998 and 2004. Vaginal delivery and maternal smoking among infants of mothers receiving systemic antibiotic treatment before delivery were independent predictors for neonatal colonization with CA-MRSA. Clearly, CA-MRSA clones have emerged as a major cause of MRSA colonization in high-risk newborns.

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