Breast infections - Microbiology and treatment in an era of antibiotic resistance.

INTRODUCTION: Primary breast abscesses occur in <1% of non-lactating women, rising to 11% in women with lactational mastitis. In patients undergoing breast cancer surgery, the inflammatory response to post-operative surgical site infection (SSI) has been implicated in recurrence. Anti-microbial resistance increasingly hampers treatment in each group.

AIMS: Describe the demographic and predisposing characteristics of patients with primary breast abscesses and secondary infections, identify the microbial and antimicrobial patterns and formulate an evidence-based protocol for treating breast infections.

METHODS: Retrospective cohort study of all breast infections (primary and post-operative) treated at UHL from 2014 to 2017. Data collected from microbiology databases and patient records was analysed using Minitab V18.

RESULTS: 537 cultures from 108 patients were analysed. 47 (43.5%) had primary abscesses, 12 (11.1%) were lactational and 49 (45.4%) were post-operative SSI. For primary infections, the mean age was 41.9 (±12.2) and reinfection rate 33%. For SSIs the mean age was 51.8 (±14.52) and reinfection rate 11.8%. Overall, 29.3% were smokers, 6.4% diabetic and 2.9% pregnant. 60 (43%) patients required radiological drainage and 2 (1%) surgical drainage. 57.5% had mixed growth. The most common isolate was Staphylococcus aureus; cultured in 16.7% of primary abscesses and 24% of SSIs. 13 empiric antibiotic regimes were prescribed before 26.4% of patients changed to 12 different targeted regimes.

CONCLUSION: Breast infections are frequently polymicrobial with a wide variety of organisms isolated, suggesting the need for broad spectrum coverage until culture results become available. Based on our local culture results, the addition of clindamycin to flucloxacillin would provide excellent empiric coverage for all categories of breast infection. An evidence-based treatment guideline is required and should be formulated in close collaboration with microbiology specialists.