Predictors of Staphylococcus aureus Rectovaginal Colonization in Pregnant Women and Risk for Maternal and Neonatal Infections

Staphylococcus aureus infections are increasing in pregnant and postpartum women and in healthy neonates and infants hospitalized in neonatal intensive care units (NICUs) [1–4]. Much of this increase has been driven by a rise in methicillin-resistant S. aureus (MRSA), specifically community-associated (CA)–MRSA, which most commonly causes infections in patients without traditional risk factors [2, 3, 5]. S. aureus infections appear to be more frequent among individuals who are colonized with S. aureus in the anterior nares and other sites [6, 7]. S. aureus has been reported to colonize the vagina in 4%–22% of pregnant women [8–12]. The prevalence of MRSA rectovaginal colonization has been reported to range 0.5%–10% [8–12]. We previously conducted a prospective surveillance study of pregnant women undergoing routine screening for colonization with group B Streptococcus (GBS) [12]. The prevalence of methicillin-susceptible S. aureus (MSSA) rectovaginal colonization was 11.8%, and the prevalence of MRSA colonization was 0.6%. All 18 MRSA strains were CA-MRSA strains and 12 of 18 (75%) were the epidemic USA300 clone. The factors that contribute to S. aureus rectovaginal colonization in pregnant women are not well understood. One study identified black race as an independent risk factor for MRSA rectovaginal colonization [10]. We identified younger age and GBS colonization as risk factors for S. aureus rectovaginal colonization but did not explore other demographic or maternal factors associated with S. aureus colonization [12]. A prior case-control study conducted among 117 women at our institution found that GBS colonization was a risk factor for MSSA rectovaginal colonization but was protective against MRSA colonization and that demographic factors and postpartum complications were not associated with colonization [13]. A few studies have examined the association between S. aureus colonization in pregnant women and the frequency of infections in women and/or their infants [9, 10, 14]. In one study, S. aureus colonization of the nares and/or vagina was not associated with an increased risk of S. aureus infections in the women, but infections in their infants were not assessed [9]. Another study did not demonstrate an increased risk of neonatal infections following neonatal S. aureus colonization in the first 48 hours of life, but maternal infections were not assessed [14]. Although vertical transmission has been proposed as a possible mechanism of maternal-to-infant transmission of MRSA [4, 10, 14, 15], the risk of developing early-onset neonatal sepsis caused by MRSA is not increased in infants born to MRSA-colonized women [10]. To date, the clinical significance of S. aureus rectovaginal colonization as a predictor of subsequent infection in mothers and their infants has not been systematically examined in a large cohort. The objectives of this study were to identify risk factors for S. aureus rectovaginal colonization, to assess maternal S. aureus colonization as a risk factor for infection among mothers and infants, and to determine the frequency of S. aureus infections in pregnant and postpartum women and their infants.