An outbreak of bilateral photokeratitis and eyelid erythema following exposure to an artificial source of ultraviolet radiation, Tamil Nadu, India, 2018

Metal halide lights (MHLs) emit ultraviolet radiation (UVR) and should be used with enclosed fixtures. We investigated a cluster of blurred vision in a locality in South India reported among light music event attendees to identify risk factors.

Methods: We searched for attendees with any eye-related symptoms by door-to-door. We described cases by time, place, and person and inspected the environment to generate a hypothesis. We followed-up the cohort of the attendees to examine the hypothesis of exposure to MHL as the cause of the outbreak. We computed relative risk (RR) and 95% confidence interval (CI) by comparing attack rates among attendees by seating location and duration of exposure.

Results: Of the total 500 attendees, we could interview 319 (64%) and 89% (284/319) attendees developed bilateral photokeratitis (median age = 24 years [range: 2-80 years]). Attack rate was higher among female (92% [172/189]) than male (85% [110/130]). Attack rate among those seated within 12 meters from dais was higher (95% [241/253]) than the rest (65% [43/66]; RR = 1.5; 95% CI = 1.2, 1.7) and attack rate was higher among those continuously exposed to MHL (97% [268/277]) than others (38% [16/42]; RR = 2.5; 95% CI = 1.7, 3.7). The duration of exposure was associated with increased risk of bilateral photokeratitis (χ² test for linear trend = 74; P < 0.00001). During the environmental inspection, we identified the use of MHL with a broken outer envelope.

Conclusions: Photokeratitis was associated with exposure to UVR from MHL with a broken outer envelope. We recommended the usage of MHL along with enclosed fixtures.