Main Menu Browse by Day or Program Author Keywords

402 Mupirocin-Resistant Methicillin-Resistant Staphylococcus aureus in Mothers and Newborns

Saturday, March 20, 2010: 10:45 AM
International North (Hyatt Regency Atlanta)
David S. Yassa, MD , Beth Israel Deaconess Medical Center, Boston, MA
Satish K. Pillai, MD , Beth Israel Deaconess Medical Center, Boston, MA
Howard S. Gold, MD , Beth Israel Deaconess Medical Center, Boston, MA
Lata Venkataraman, M., Sc. , Beth Israel Deaconess Medical Center, Boston, MA
Toni H. Golen, MD , Beth Israel Deaconess Medical Center, Boston, MA
Munish Gupta, MD, MMSc , Beth Israel Deaconess Medical Center, Boston, MA
DeWayne M. Pursley, MD , Beth Israel Deaconess Medical Center, Boston, MA
Matthew E. Wise, PhD , Division of Healthcare Quality Promotion, CDC, Atlanta, GA
Brandi M. Limbago, PhD , Division of Healthcare Quality Promotion, CDC, Atlanta, GA
Rachel Gorwitz, MD, MPH , Centers for Disease Control and Prevention, Atlanta, GA
Linda Baldini, RN , Beth Israel Deaconess Medical Center, Boston, MA
Fatima Muriel, MT , Beth Israel Deaconess Medical Center, Boston, MA
Sharon B. Wright, MD, MPH , Beth Israel Deaconess Medical Center, Boston, MA

Background:

Community-associated methicillin-resistant Staphylococcus aureus (MRSA) has caused outbreaks in nurseries, maternity units and neonatal ICUs.  High level mupirocin resistance (HL mupR) is conferred by the mupA gene, frequently associated with a conjugative, pSK41-like plasmid, and may impact prevention and treatment in this population.

Objective:

To characterize HL mupR in an outbreak of MRSA skin and soft tissue infections among mothers and newborns.

Methods:

A case was defined as an MRSA infection occurring any time after discharge in a mother or baby with a delivery date from 10/27/08 to 9/11/09 associated with an isolate that was pulsed-field gel electrophoresis (PFGE) type USA300-0114 or not typed. Mupirocin susceptibility testing by E-test (ABBioMerieux, Durham, NC) and PFGE were performed on available isolates. Plasmid DNA was isolated from 12 USA300-0114 isolates (6 were HL mupR), digested with BanII and BanII/ClaI and run on 0.9% agarose gels. Risk factor data was collected by review of hospital and pediatrician records. Univariate associations with HL mupR among case patients were analyzed by t-test and 2-sample test of proportion.

 

Results:

In the first 180 days of the outbreak, 74 MRSA infections (29 in mothers, 44 in newborns) were identified. 73 met the case definition: 59 isolates were type USA300-0114 and 14 isolates were not typed. HL mupR emerged near the end of the first 60 days of the outbreak and predominated thereafter. 45/46 isolates tested were susceptible to clindamycin.  Case characteristics by 60-day interval are shown in the Table. 

Infection with a HL mupR strain was significantly associated with identification of group B beta-hemolytic streptococcus (GBS) on maternal rectovaginal prenatal screen (p=0.0057), receipt of intrapartum (IP) antibiotics (p=0.0001), and a shorter time between discharge and infection onset (p=0.053).  Maternal age, gestational age, mode of delivery, birth weight and circumcision were not significantly associated with infection with a HL mupR strain.

Mupirocin-susceptible (mupS) and HL mupR strains were indistinguishable by PFGE, however plasmid restriction patterns differed between mupS and mupR isolates.

Conclusions:

HL mupR emerged during this, the largest outbreak of MRSA USA300 among mothers and newborns reported to date. IP antibiotics appeared to be a risk factor for HL mupR. Shorter time to infection may suggest altered virulence in HL mupR strains. The distinctive plasmid restriction pattern within each phenotype suggests either introduction of a new mupR USA300 strain or insertion of a mupA element into the outbreak strain. While prior reports demonstrated clindamycin resistance in mupR strains with pSK41-like plasmids, this mupR outbreak strain was susceptible to clindamycin. Concomitant HL mupR and mupS infections during the outbreak suggest the possibility of two distinct strains with unique transmission characteristics.