Methicillin-resistant Staphylococcus aureus (MRSA) infections were typically found in hospitals and long-term care facilities, but they have now been reported in the community and in other health facilities. These infections, including sepsis, necrotizing pneumonia, and a variety of serious skin and soft tissue infections, often are caused by highly virulent strains of MRSA that are resistant to several antibiotics. MRSA infection outbreaks have been documented in pregnant and postpartum women and in infants in neonatal intensive care units. Because the prevalence of MRSA in pregnant women and the potential for outbreaks of MRSA infections in obstetric and neonatal units are poorly understood, Chen and colleagues conducted a prospective surveillance study of women receiving prenatal care at a large urban university medical center.

Researchers used swabs collected from routine group B streptococcus (GBS) screening. Rectal and vaginal specimens also were collected from pregnant women who were between 35 and 37 weeks’ gestation and from those at risk of preterm delivery. The specimens were cultured under standard conditions for GBS and S. aureus. All S. aureus strains were tested for susceptibility to various antimicrobial agents.

During the six-month study, 2,963 specimens were processed for S. aureus; 507 (17 percent) were positive. In 190 cases, GBS and S. aureus were present in the same patient. Of the S. aureus isolates, 14 (2.8 percent) were MRSA. Thirteen of these were determined to be community-associated MRSA organisms that were susceptible to several common antibiotics, as opposed to being health care–associated MRSA, which is multidrug resistant.

The authors conclude that the overall prevalence of S. aureus in vaginal-rectal cultures from pregnant women is about 17 percent. This is significantly greater than previous estimates, which were based on studies of cultures from different sites and from pregnant women in other countries. They also note thatS. aureus colonization was significantly associated with GBS. Although the prevalence of MRSA in the pregnant women screened was small (about 0.5 percent), it does raise the possibility of outbreaks of serious infection in obstetric or neonatal units. Case reports have suggested a potential for transmission of MRSA from mothers to infants. The authors conclude that MRSA could be an emerging threat of infection in maternal and neonatal populations.