Grading contact lens-related microbial keratitis: relevance to disease burden

To describe a clinical grading system for epidemiological investigation of presumed contact lens related microbial keratitis (MK) and investigate the relationship to associated costs and disease duration.

Eligible cases identified via surveillance required positive culture or presence of at least one clinical criterion: part of the lesion within the central 4 mm of the cornea, any anterior chamber reaction, or significant pain. Two reviewers graded cases as severe MK with vision loss (two lines), severe MK without vision loss (positive culture or central location, peripheral but >2 mm or with a hypopyon) or mild MK (remainder). The medical care, pathology, and medications comprised direct costs and loss of income, assistance of carers, and purchase of spectacles comprised indirect costs; these were calculated in Australian dollars (AU$). Duration of disease was estimated from duration of symptoms (days). Outcome measures were compared between categories using a one way analysis of variance (ANOVA).

There were 47 of 278 (16.3%) severe with vision loss, 137 of 278 (49.3%) severe without vision loss, and 94 of 278 (33.8%) mild MK. The disease duration was 18 (6 to 95) [median (inter-quartile range)] for severe cases with vision loss, 7 (4 to 14) for severe cases without vision loss, and 4 (3 to 7) days for mild MK (ANOVA, p < 0.001). Associated costs were AU$5515 (2784 to 9437) for severe cases with vision loss, AU$1596 (774 to 4888) for severe cases without vision loss, and AU$795 (527 to 1234) for the mild MK (ANOVA, p < 0.001). Costs and symptom duration were greatest for severe disease with vision loss, less for the severe disease without vision loss, and lowest for the mild disease (p < 0.003).

The comparison of disease burden lends support to this clinical grading system and the concept that the severity of MK can be stratified to identify those that might be of non-infectious etiology or have a microbial cause of low virulence with minimal morbidity.