Association Between Season, Temperature and Causative Organism in Microbial Keratitis in the UK

Purpose: Microbial keratitis (MK) is a major cause of corneal blindness worldwide. Variations in season and temperature can affect MK incidence due to specific causative organisms; however, few studies have examined these factors in the UK. Methods: Retrospective review of all corneal scrapes from patients with MK presenting to Manchester Royal Eye Hospital, UK, between January 2004 and December 2015. Manchester's monthly temperature data were obtained from Met Office UK. Analysis was performed using logistic regression. Results: From 4229 corneal scrapes, 1539 organisms grew (90.6% bacteria, 7.1% fungi, and 2.3% Acanthamoebae sp.). Gram-positive bacteria grew with increasing temperature [odds ratio (OR) 1.62, 95% CI: 1.11-2.39, P = 0.014], and fungi grew with decreasing temperature (OR 0.29, 95% CI: 0.16-0.51, P < 0.001). Moraxella sp. grew with decreasing temperature (OR 0.91, 95% CI: 0.86-0.96, P = 0.001). Compared with winter, overall culture positivity was significantly less likely in summer (OR 0.57, 95% CI: 0.38-0.87, P = 0.008) and spring (OR 0.65, 95% CI: 0.43-0.99, P = 0.045). Gram-negative bacteria were more likely in summer (OR 1.48, 95% CI: 1.06-2.09, P = 0.022) and autumn (OR 1.75, 95% CI: 1.24-2.47, P = 0.001). Candida sp. were less likely in summer (OR 0.25, 95% CI: 0.07-0.82, P = 0.027) and autumn (OR 0.18, 95% CI: 0.05-0.62, P = 0.009), and Acanthamoeba sp. were less likely in summer (OR 0.39, 95% CI: 0.15-0.92, P = 0.037) and spring (OR 0.26, 95% CI: 0.08-0.69, P = 0.011). Conclusions: Herein we report variation in the incidence of MK-causing organisms by season and temperature; this finding may aid clinicians in predicting possible causative organisms for MK at differing times of the year.