Risk Factors and Outcomes among Post-partum Women with Staphylococcus aureus Breast Abscesses in the Era of Community-Associated Methicillin Resistance

Background: Breast abscesses are a complication of breast-feeding; however, little is known about risk factors for their development or outcomes. 

Objective: To identify clinical predictors of post-partum Staphylococcus aureus (SA) breast abscesses and associated outcomes.     

Methods: We conducted a case-control study of women who delivered babies in our urban tertiary care center with a high-volume obstetrics service between 10/08-4/10. Cases were post-partum women with culture-confirmed SA breast abscesses within 1 year of delivery between 10/08-8/10; most were part of a previously described cluster of community-associated MRSA (CA-MRSA) skin and soft tissue infections. Controls were matched on closest delivery time on the delivery date, and then by admission date, when possible. Pulsed-field gel electrophoresis was used for SA typing.  Data were collected from electronic administrative databases and medical records. Potential risk factors for development of breast abscess were analyzed by Chi square or T test as appropriate using SAS version 9.1.3 (Cary, NC). Variables significant to the p<0.2 level were included in a multivariable logistic regression analysis. Outcome measures, including readmission rate and breast-feeding cessation, were evaluated in a separate analysis. 

Results: Of 7442 deliveries during the study period, 33 met the case definition of culture-confirmed post-partum SA breast abscess.  27 (82%) had MRSA, predominantly USA300-0114. The remaining 6 had methicillin-susceptible SA.  Risk factors significant to p≤0.05 level on univariate analyses are shown in the Table. On multivariable analysis, identification of maternal breast-feeding difficulties by a lactation consultant prior to discharge was the only factor associated with a higher risk of breast abscess (OR 4.8, 2.0-11.6). There was a trend toward increased risk of abscess in working mothers. Patients with breast abscess had a higher readmission rate (p<0.001), and increased resource utilization (mean of 4.4 breast sonograms). 73% of cases required drainage procedures, and 48% required readmission. 12% developed complications as a result of their abscess, primarily milk fistulas. 39% permanently stopped breast-feeding due to the abscess. 

Conclusions: Breast abscesses in the era of CA-MRSA were often preceded by in-hospital maternal breast-feeding difficulties.  A high rate of adverse outcomes, including readmission and breast-feeding cessation, was associated with SA breast abscesses.

Risk Factor	OR, Univariate	P-value
Mother with breast-feeding difficulties (yes/no)	5.1 (2.1-12.3)	0.003
Working Mother (yes/no)	3.3 (1.1-10.3)	0.036
Pumping in Hospital (yes/no)	2.6 (1.1- 5.9)	0.025
Maternal age at delivery (per year)	1.1 (1.0-1.2)	0.037
Parity (per prior child)	0.50 (0.27-0.98)	0.044