Methicillin-Resistant Staphylococcus aureus breast abscesses: Risk factors and outcomes from a tertiary care center of a lower-middle-income country

Abstract

Background and Objectives: Breast abscesses are a common complication of mastitis, traditionally caused by methicillin-sensitive Staphylococcus aureus (MSSA). Recent global reports, however, indicate a rising prevalence of methicillin-resistant Staphylococcus aureus (MRSA), with limited data from South Asia. To determine the prevalence, risk factors, antibiotic susceptibility patterns, management strategies, and clinical outcomes of MRSA breast abscesses at a tertiary-care center in Pakistan.

Methodology: A retrospective cross-sectional study was conducted at Aga Khan University Hospital, Karachi, from January 2010 to December 2024. All culture-positive breast abscesses with S. aureus growth were included. Patient demographics, clinical features, microbiological data, management, and outcomes were analyzed using descriptive statistics.

Results: Of 366 culture-positive breast abscesses, 326 (89.0%) yielded S. aureus, of which 274 (74.8% out of total) were MRSA, representing 74.5% of all isolates. A marked temporal shift was observed: MSSA remained relatively common from 2010–2019, but only 14 MSSA cases occurred from 2020–2024, with MRSA becoming the dominant pathogen. The mean age of MRSA patients was 29.4 ± 7.1 years; 88.7% were lactational. Key risk factors included prior antibiotic exposure (63.0%), recent hospitalization (55.9%), diabetes (18.6%), and history of previous abscess (14.4%). All MRSA isolates were vancomycin-susceptible; resistance rates were low for clindamycin (11.7%) and trimethoprim–sulfamethoxazole (9.8%). Initial ultrasound-guided aspiration was performed in 60.2%, with 20.6% requiring subsequent incision and drainage. Empirical clindamycin was used in 53.6%. Complete resolution was achieved in all patients with documented follow-up, with a recurrence rate of 3.3%. Among lactational cases, 91.4% successfully resumed breastfeeding.

Conclusion: This study reports one of the highest documented MRSA prevalence rates (74.5%) in breast abscesses worldwide, with a clear post-2020 dominance. Despite high MRSA burden, excellent outcomes were achieved with ultrasound-guided drainage and susceptibility-guided antibiotics. In high-prevalence settings, empirical therapy must cover MRSA, and routine culture with sensitivity testing is strongly recommended. Ultrasound-guided aspiration should remain first-line management, and continued breastfeeding is safe and encouraged after treatment.