Temporal and seasonal trends in acanthamoeba keratitis

PURPOSE: The purpose of this study was to assess the incidence and risk factors of Acanthamoeba keratitis (AK) over an 8-year period in a Canadian tertiary care setting. METHODS: We retrospectively reviewed the medical records of 41 patients (42 eyes), who were diagnosed as having AK between January 1999 and December 2006 in the cornea clinic at the Toronto Western Hospital. The incidence and risk factors of AK were evaluated. RESULTS: The number of cases per year increased from between 0 and 4 in the first 5 years to 9, 14, and 8 in the last 3 years. The annual increasing trend was statistically significant (P = 0.04). The month of onset of disease symptoms showed a trend toward onset in summer and fall and was statistically significant for the difference between January and August (P = 0.0094). The season of onset of disease symptoms showed a trend toward summer onset, and the difference between winter and summer was statistically significant (P = 0.02). 92.9% of cases occurred in contact lens wearers, particularly in soft contact lens wearers (82.1%). CONCLUSIONS: The incidence of AK in Canada may be increasing since 2004. There is a seasonal trend toward disease onset in the warmer months.