404 Epidemiology of Staphylococcus aureus carriage in pregnancy: Peripartum transmission rates and adverse outcomes

Saturday, March 20, 2010: 11:15 AM
International North (Hyatt Regency Atlanta)
Janet I. Andrews, MD , University of Iowa, Iowa City, IA
Diedre K. Fleener, BSN , University of Iowa, Iowa City, IA
Shawn A. Messer, MPH , University of Iowa, Iowa City, IA
Daniel Diekema, MD , University of Iowa College of Medicine and Hospitals and Clinics; Iowa City Veterans' Affairs Medical Center, Iowa City, IA
Background: Staphylococcus aureus (SA), including methicillin-resistant SA (MRSA), commonly cause disease in the peripartum period, and neonates are vulnerable to morbidity and mortality from SA disease. Although SA infections and outbreaks in neonates have been linked to infected or colonized mothers, there is little data on the epidemiology and outcomes of SA carriage among pregnant women.
Objective: To determine the rate of SA (including MRSA) carriage among pregnant women and their newborns, the peripartum transmission rate of SA from women to their newborns, and the rate of adverse infectious outcomes among SA carriers versus non-carriers.
Methods: We performed cultures for SA carriage from nares, throat, skin, vagina and rectum of women at 35-37 weeks gestation. We also cultured their infants (nares and umbilicus) prior to hospital discharge. Standard culture methods, including broth enrichment, were used. Antimicrobial susceptibility and pulsed field gel electrophoresis (PFGE) was performed for all SA isolates.  We monitored both women and infants for selected peripartum infectious adverse outcomes (SA infections, C-section wound infection, chorioamnionitis and suspected neonatal sepsis (infants receiving > 3 days of antibiotics)).
Results: We screened 433 women, 125 (29%) of whom had at least one culture positive for SA, while 21 (5%) of 423 infants were SA carriers. Nares culture only, without broth enrichment, detected fewer than half of maternal SA carriers, but addition of broth enrichment and throat culture detected 90% of carriers.  Vaginal SA carriage was present in 12 women (3%). Only 6 (1.4%) women and 3 (0.7%) neonates carried MRSA.  SA carriage was more common among the 85 women with Group B streptococcus (GBS) carriage (39%, versus 26% among GBS-negative, p=0.02). The maternal-infant SA transmission rate (at time of infant hospital discharge) was 6% (8/125).  Thirteen of 21 (62%) infant SA carriers were born to SA non-carrier mothers. There was only one instance of maternal-infant MRSA transmission.  The rate of maternal and infant infectious adverse outcomes was no different between maternal SA carriers and non-carriers.  Suspected neonatal sepsis (receipt of > 3 days of antibiotics) was documented in 17/125 infants born to SA carriers and 42/308 infants born to non-carriers (14% in both groups, NS).
Conclusions: SA and MRSA carriage among pregnant women approximated that in the general population (J Infect Dis 2008;197:1226); MRSA carriage was unusual.  Maternal-infant transmission rate of SA was low in the immediate postpartum period.  Over half of infants with SA carriage before hospital discharge appear to acquire the organism from a non-maternal source, and SA disease and infectious adverse outcomes were not greater among maternal carriers than non-carriers. Our data do not support routine maternal SA screening as part of peripartum infection prevention strategies.