Incidence of Acanthamoeba Keratitis in the United Kingdom in 2015: A Prospective National Survey

PURPOSE: The aims of this study were to quantify the incidence of Acanthamoeba keratitis (AK) in the United Kingdom and investigate risk factors and management parameters. METHODS: This was a prospective population-based study from January to December 2015 through the British Ophthalmic Surveillance Unit. Data were collected on demographics, clinical features, and management. Incidence rates were calculated from estimates of population and contact lens (CL) user numbers. Statistical analysis compared annualized incidences per million and altered risk ratios for AK with the England and Wales 24 months 1997/1998 to 1998/1999 study. RESULTS: The study identified 124 AK cases, an overall incidence of 2.35 per million. CL wearers accounted for 108 of 124 cases (87%), in whom the AK incidence was 26.94 per million. Herpes keratitis was initially misdiagnosed in 25 of 124 cases (20.2%). The highest incidence of AK was among planned replacement soft CL (PRSCL) wearers (50.65 per million), 7-fold greater than for daily disposable CL (DDSCL) users (7.24 per million). There was a significant increase in AK incidence ( P < 0.001) compared with both 1997/1998 [risk ratio 1.92, 95% confidence interval (CI) 1.38-2.66] and 1998/1999 (risk ratio 2.13, 95% CI 1.52-2.98) together with a higher incidence per million CL users of 26.94 versus 21.14 (1997/1998) and 17.53 (1998/1999). CONCLUSIONS: This study provides the first published data on the nationwide incidence of AK in the United Kingdom. The findings confirm an increasing incidence of AK, particularly among contact lens wearers since 1997/1998 to 1998/1999. PRSCLs were identified as a significant risk factor compared with DDSCLs. Misdiagnosis and treatment delays remain an ongoing problem for patients with AK.