No abstract

Aim: To determine the incidence, regional variation in frequency, outcome, and risk factors for acanthamoeba keratitis (AK) in England and Wales. Methods: AK cases presenting from 1 October 1997 to 30 September 1999 were identified by the British Ophthalmic Surveillance Unit active reporting system. Clinical and patient postal questionnaire data were analysed. Results: 106 reported cases met study criteria. The annual incidence for the 2 years was 1.26 and 1.13 per million adults and, for contact lens (CL) wearers, 21.14 and 17.53 per million. There was marked regional variation in incidence (0 to 85.13 per million adult CL wearers), with CL wearers in the south having a ninefold increased risk of AK compared with those resident in the north (95% confidence limits: 2.2-38.9, p<0.0001), and a threefold increased risk with hard as opposed to soft domestic water (95% confidence limits: 1.73 to 6.58, p<0.001). Treatment and outcome data were similar to those previously reported. 93/106 (88%) patients were CL wearers. Among these, 46/77 (60%) were disinfecting irregularly, and 20/63 (32%) had been swimming in CLs. One step hydrogen peroxide and chlorine release soft CL (SCL) disinfection systems were significantly over-represented among the cases. Among SCL users, one or more previously established risk factors for AK were identified in 50/55 (91%) patients. Conclusions: The incidence was considerably higher than most previous estimates, and was static. The geographical variation in incidence may be partly related to the increase in risk associated with hard water. The fact that water quality can have such an effect on the risk of AK suggests that many CL wearers must be letting tapwater come into contact with their lenses or storage cases. Improved education for CL wearers and practitioners about hygiene practice and the variable efficacy of contact lens systems could be expected to reduce the incidence of this disease.

Conclusions-Earlier diagnosis and more eVective medical therapy have improved the prognosis for most AK patients. The study demonstrates the highly preventable nature of the disease: 91% of the SCL wearers could have avoided the disease by refraining from inadvisable practices, and a marked fall in frequency was seen after intensive media attention to AK, possibly in conjunction with increasing penetrance of new CL products. Since the frequency of AK appears to be largely determined by the ever changing trends in CL use, continued monitoring is indicated.

AK is a largely preventable disease. The current outbreak is unlikely to be due to any one of the identified risk factors in isolation. Improving CL and hand hygiene, avoiding CLs contamination with water and use of effective CL disinfection solutions, or daily disposable CLs, will reduce the incidence of AK. In the longer-term, water avoidance publicity for CL users can be expected to reduce the incidence further. Ongoing surveillance of AK numbers will identify changes in incidence earlier. Evaluation of contamination in end-user drinking water would contribute to our understanding of regional variations in the risk of exposure.