Risk Factors for Methicillin-Resistant Staphylococcus aureus (MRSA) Colonization Among Patients Admitted to Obstetrical Units: A Nested Case-Control Study.

OBJECTIVE: Methicillin-resistant Staphylococcus aureus (MRSA) among obstetrical patients can increase birth complications for both mothers and infants, but little is known about the risk factors for MRSA in this population. The objective of this study was to determine the prevalence of MRSA among obstetrical patients and identify risk factors associated with MRSA colonization.

METHODS: This nested case-control study used obstetrical patients with MRSA colonization identified through a universal screening program at The Ottawa Hospital (February 2008-January 2010). Cases and three matched controls were compared using chi-square tests for categorical variables, median and interquartile range (IQR), and Wilcoxon rank-sum tests for continuous variables. Conditional logistic regression using ORs and 95% CIs was used to identify risk factors. Standard microbiologic techniques and pulsed-field gel electrophoresis of the MRSA isolates from case patients were performed.

RESULTS: Out of 11 478 obstetrical patients, 39 (0.34%) were MRSA colonized; 117 patients were selected as matched controls. The median age was 30 (IQR 27.5-35.00) and median length of stay was 2.55 days (IQR 1.95-3.24). Only MRSA cases had a previous MRSA infection (4 vs. 0). MRSA cases had significantly higher parity (median 3; IQR 2-5) compared with controls (median 2; IQR 1-3) (OR 1.52; 95% CI 1.22-1.90) CONCLUSION: This study identified a low prevalence of MRSA among obstetrical patients. Risk factors associated with MRSA colonization were previous MRSA infection and multiparity. Obstetrical patients who previously tested positive for MRSA should be placed on contact precautions at the time of hospital admission because this is a risk factor for future colonization.