354. Risk Factor Analysis of Nosocomial MRSA Infection in Pospartum Women and Newborns using a Cluster-based Case Control Study
Session: Poster Abstract Session: MRSA, MSSA, Enterococci
Thursday, October 3, 2013
Room: The Moscone Center: Poster Hall C

Background:   A large number of methicillin-resistant Staphylococcus aureus (MRSA) infections occurred in newborns and post-partum women (PPW) at our institution over a 5 year period, largely in the context of a 3 year outbreak of MRSA USA300-0114.  The interdependence of potential risk factors in a PPW-newborn pair make analysis challenging.  We sought to evaluate risk factors associated with MRSA infections in this population, treating each pair as a cluster.

Methods:   PPW-newborn pairs delivered between 9/07 and 6/12 were enrolled in a case-control study.  Cases were defined as pairs in which 1 or both members had a culture-confirmed MRSA infection within 1 year after delivery.  Controls were selected from pairs without infection.  Case and control clusters were matched based on closest delivery time with 3 controls per case.  Exclusion criteria included neonatal ICU stay >24 hours, non-viable delivery, and multiple births.  Data on patient and hospital risk factors for MRSA were abstracted from medical records.  Variables with p£0.1on univariate analysis were included in the multivariable conditional logistic regression using stepwise selection (p £ 0.10 for entry and £0.15 for retention).  All analyses were performed using SAS v.9.3.

Results:   80 case and 239 control clusters were identified from among 19,886 eligible PPW-newborn pairs. The results of the multivariable model are shown below.   The c-statistic for the model was 0.76. 


Odds Ratio

95% CI

Baby prolonged length of stay (LOS)


1.65, 10.29



0.62, 3.28

Cesarean delivery


0.83, 2.76

Public insurance*


0.13, 1.13



1.03, 3.36

Mom admission in prior year*


0.07, 0.71

*Sparse data in some categories

Conclusion:   In this study conducted partially during a nosocomial outbreak of MRSA, prolonged LOS and primiparity predisposed PPW-newborn pairs to MRSA infection.  Admission of the PPW in the year prior to delivery was protective, possibly as a marker for increased prenatal care.  Circumcision, delivery type, and insurance type trended to but did not reach significance.  Treating PPW-newborn pairs as units of observation may provide a novel way of examining the effects of risk factors on infection outcomes that are highly correlated.

David S. Yassa, MD1, Baevin S. Carbery, MPH1, Jocelyn A. Pedrick1, Long H. Ngo, PhD2, Munish Gupta, MD, MMSc3, George M. Eliopoulos, MD1, Howard S. Gold, MD1 and Sharon B. Wright, MD MPH1, (1)Medicine, Division of Infectious Diseases, Beth Israel Deaconess Medical Center, Boston, MA, (2)Medicine, Division of General Medicine, Beth Israel Deaconess Medical Center, Boston, MA, (3)Neonatology, Beth Israel Deaconess Medical Center, Boston, MA


D. S. Yassa, None

B. S. Carbery, None

J. A. Pedrick, None

L. H. Ngo, None

M. Gupta, None

G. M. Eliopoulos, None

H. S. Gold, None

S. B. Wright, None

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