Characterization of Polymicrobial and Antibiotic-Resistant Infectious Keratitis in a County Hospital Setting

Purpose: Infectious keratitis is a serious cause of visual impairment, particularly in low-income communities. This study examines the associations between social risk factors and polymicrobial keratitis, multidrug resistance, pathogen spectrum, and outcomes at a county hospital. Methods: We performed a retrospective study of Zuckerberg San Francisco General Hospital patients treated for infectious keratitis from 2010 to 2021. Multivariable regression was performed to analyze the relationships between social, medical, and psychiatric risk factors with polymicrobial growth, multidrug resistance, and clinical outcomes. Results: Of 174 patients with infectious keratitis, 44 (25%) had polymicrobial growth. Six patients (14%) with polymicrobial growth had multidrug-resistant organisms. Homeless patients were more likely to present with polymicrobial infection (odds ratio [OR] 3.4, P = 0.023), and polymicrobial infections were associated with multidrug-resistant organisms ( P = 0.018). Smoking, drug use, HIV positivity, prior corneal pathology, and contact lens use were not associated with an increased risk of polymicrobial infection. Eleven patients (6.3%) were started on topical antibiotics before presentation; of these, none developed polymicrobial infections or multidrug-resistant organisms. Polymicrobial infections increased the likelihood to initiation of fortified antibiotics (OR 2.9, P = 0.011) but did not impact ulcer size, final visual acuity, time to resolution, or likelihood of emergent procedures. Conclusions: Homelessness correlates with an increased risk of polymicrobial keratitis and subsequent multidrug resistance, supporting initiation of broad antibiotic coverage in this population. Prior topical antibiotics did not increase risk of polymicrobial infection. Polymicrobial infection did not significantly worsen clinical outcomes.