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Genital Tract Methicillin-Resistant Staphylococcus aureus: Risk of Vertical Transmission in Pregnant Women

Andrews, William W. PhD, MD; Schelonka, Robert MD; Waites, Ken MD; Stamm, Alan MD; Cliver, Suzanne P.; Moser, Stephen PhD

doi: 10.1097/01.AOG.0000298344.04916.11
Original Research

OBJECTIVE: To estimate the frequency of genital tract colonization by methicillin-resistant Staphylococcus aureus (MRSA) among pregnant women and evaluate the association of such colonization with infant outcome.

METHODS: Between July 2003 and July 2006, anovaginal screening cultures for group B Streptococcus (GBS) were prospectively obtained in the third trimester (35 to less than 37 weeks of gestation) and were also processed for identification of Staphylococcus aureus including methicillin-resistant strains. Maternal colonization by MRSA was linked to a computerized database of invasive neonatal infections that occurred at our center during the study period.

RESULTS: Among 5,732 mothers (who delivered 5,804 infants) with GBS screening cultures and infant infection data available, 22.9% were GBS-positive and 14.5% were positive for Staphylococcus aureus. A total of 24.3% of the Staphylococcus aureus isolates were MRSA. The overall MRSA colonization rate was 3.5%. Colonization by any Staphylococcus aureus (relative risk 1.6, 95% confidence interval 1.4–1.9) as well as MRSA (relative risk 2.2, 95% confidence interval 1.6–2.8) was significantly more common among GBS-positive than among GBS-negative women. No cases of early-onset invasive neonatal infection by MRSA occurred among infants in the study.

CONCLUSION: Genital tract colonization with MRSA affected 3.5% of pregnant women. Such MRSA colonization is associated with colonization by GBS but does not predispose to a high risk of early-onset neonatal MRSA infection.


Genital tract methicillin-resistant Staphylococcus aureus colonization is common, but it is not associated with a high risk of vertically transmitted, invasive, early-onset neonatal infection.

From the Departments of 1Obstetrics and Gynecology, 2Pediatrics, 3Pathology, and 4Internal Medicine, Center for Research in Women's Health, University of Alabama at Birmingham.

Supported in part by a grant from the University of Alabama at Birmingham Health Services Foundation General Endowment Fund.

Corresponding author: William W. Andrews, PhD, MD, Department of Ob/Gyn, University of Alabama at Birmingham, OHB 458, 619 19th Street South, Birmingham, AL 35249-7333; e-mail:

Financial Disclosure The authors have no potential conflicts of interest to disclose.

© 2008 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.