Genital tract methicillin-resistant Staphylococcus aureus: risk of vertical transmission in pregnant women.

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.

LEVEL OF EVIDENCE: III.