Correlation between surface water contamination with amoeba and the onset of symptoms and diagnosis of amoeba-like keratitis.

AIM A seasonal variation was noted in the incidence of amoeba-like keratitis in Iowa. The level of contamination of amoeba in surface water has been found previously to vary on a monthly basis for Tulsa, Oklahoma, a region with a similar climate. It was hypothesised that this seasonal variation in amoeba-like keratitis correlated with the concentration of amoeba in surface water. METHODS The monthly variation in the onset of symptoms was determined and date of diagnosis in 137 cases of amoeba-like keratitis, in Iowa, from January 1993 to the end of December 1996. RESULTS Over a 4 year period a significant variation was found, on a monthly basis, in the onset of symptoms as reported by the patient. There were two peak periods per year when the onset of symptoms was most frequent: June and November. This corresponded closely with the concentration of amoeba in the ground water reported for a similar region in the mid-west (Tulsa, Oklahoma). A yearly increase was found in the number of cases diagnosed from January 1993 to the end of December 1996. CONCLUSIONS This study supports the hypothesis that the concentration of amoeba in surface water may influence the rate of an amoeba-like keratitis infection.