Methods Setting: A large county hospital in Houston, Texas.

Study Population: Patients with known diagnosis of microbial keratitis from January 2011 to May 2015.

Observation Procedure: Retrospective chart review.

Main Outcomes: Epidemiology, risk factors, outcomes and antibiotic susceptibility of microbial keratitis.

Results The most commonly identified risk factors were contact lens use (34.4%), ocular trauma (26.3%), diabetes mellitus (16.7%), ocular surgery (13.5%), ocular surface diseases (11.5%), previous keratitis (10.4%), glaucoma (6.3%), cocaine use (5.2%) and HIV-positive status (4.2%). Eyes with positive cultures (61.5%) were associated with worse visual outcomes (p=0.019) and a higher number of follow-up visits (p=0.007) than eyes with negative cultures (38.5%). Corneal perforation was the most common complication (11.5%). Gram-negative organisms (21.9%) were all susceptible to ceftazidime, tobramycin and fluoroquinolones. Gram-positive organisms (33.3%) had worse outcomes than Gram-negative organisms (21.9%) and exhibited a wide spectrum of antibiotic resistance, but all were susceptible to vancomycin. Twenty-seven per cent of the coagulase-negative Staphylococci were resistant to fluoroquinolones.

Conclusion This study identified a recent shift in risk factors and antibiotic resistance patterns in microbial keratitis at a County Hospital in Houston, Texas. In our patient population, fluoroquinolone monotherapy is not recommended for severe corneal ulcers. On the basis of these results, vancomycin and tobramycin should be used for empirical therapy until microbial identity and sensitivity results are available.