Comparative Outcomes of Exogenous and Endogenous MRSA Vs MSSA Endophthalmitis

Methicillin-resistant Staphylococcus aureus (MRSA) is associated with a worse systemic prognosis compared to methicillin-sensitive S. aureus (MSSA). Prior studies of MRSA and MSSA endophthalmitis group endogenous and exogenous cases. We performed a retrospective cohort study comparing ocular outcomes in endogenous and exogenous MRSA and MSSA endophthalmitis, representing the largest series to date (n = 46 eyes).

Endophthalmitis cases from October 2008-April 2025 were identified using ICD10 codes for endophthalmitis and Staphylococcus aureus. Cases with endophthalmitis diagnosis, culture-proven MRSA or MSSA and visual exams at presentation and within 3 months were included. Of 651 potential cases, 37 cases (46 eyes) met criteria, including 7 exogenous and 30 endogenous cases. Visual acuity was categorized as ≤20/200, >20/200 to ≤20/40, >20/40. Complications were analyzed per eye. Categorical variables were compared with a Fisher's t-test (p < 0.05).

Vision at presentation, 1 week-2 months, and 2-3 months did not differ significantly between MRSA and MSSA in exogenous or endogenous groups. The exogenous cohort had significantly higher rates of enucleation/evisceration than the endogenous cohort. Intravenous drug use and mortality were more frequent among patients with endogenous MRSA, though not statistically significant.

MRSA and MSSA endophthalmitis have similar ocular outcomes. In exogenous and endogenous cohorts, there were no significant differences in vision or complications between MRSA and MSSA endophthalmitis except that the exogenous group had a significantly higher rate of enucleation/evisceration, potentially reflecting increased organism load with direct inoculation. The higher mortality associated with endogenous MRSA infections, though not statistically significant, warrants future investigation.