Outcomes of Staphylococcus aureus Keratitis: A Retrospective Comparison of Methicillin-Resistant and Methicillin-Susceptible Isolates

Purpose: To describe the clinical characteristics, antimicrobial susceptibility profiles, treatment patterns, and outcomes of methicillin-resistant (MRSA) and methicillin-susceptible (MSSA) Staphylococcus aureus keratitis. Methods: Staphylococcus aureus isolates from corneal scrapings were collected between 2004 and 2022 at 2 tertiary centers in Vancouver, Canada, and Boston, USA. Antibiotic susceptibility profiles were recorded, and demographic data, ocular and systemic risk factors, treatment regimens, and clinical outcomes were retrospectively analyzed and compared between MRSA and MSSA keratitis cases. Results: A total of 174 patients with culture-proven S. aureus keratitis were included, comprising 104 MSSA (59.8%) and 70 MRSA (40.2%) cases. Median age was 63.5 years, and ocular surface disease was the most common local risk factor (64.5%). The cohort showed a high burden of systemic comorbidities and health care exposure in the preceding year (44.8%), with MRSA keratitis significantly associated with prior MRSA infection ( P P = 0.007). MRSA isolates had low susceptibility to fluoroquinolones (moxifloxacin 19.7%) but remained uniformly susceptible to vancomycin. Vancomycin-containing regimens predominated in both groups, commonly combined with tobramycin (52.3%). Overall visual outcomes were poor (median final BCVA 1.30 logMAR), and surgical intervention was needed in 31.6% of cases. MSSA achieved significantly better final visual acuity than MRSA (median BCVA 1.00 vs. 2.30 logMAR; P = 0.004). Conclusions: S. aureus keratitis is a vision-threatening condition with distinct clinical risk profiles and substantial morbidity. Evolving resistance patterns and worse outcomes among MRSA cases highlight the need for optimized treatment strategies and ongoing antimicrobial surveillance.