Seasonality and trends in the incidence and prevalence of gout in England and Wales 1994-2007

Objectives: To examine seasonality and long-term trends in the incidence and prevalence of gout. Methods: A retrospective study (1994-2007) using routinely collected surveillance data from the Royal College of General Practitioners Weekly Returns Service sentinel general practice network in England and Wales. New cases and acute attacks of gout per 10 000 population were calculated for age groups 0-44, 45-64, 65-74 and >= 75 years. Long-term trends of annual incidence were assessed by regression analysis. Seasonality indices were calculated using 4-weekly data, and the relative risk of gout incidence during the summer was estimated. Annual prevalence was estimated from the consulting patient population (2001-7) and from prescribing data on defined daily doses (DDD) of allopurinol (2003-7). Results: The annual incidence rate of new gout cases was stable over the period 1998-2007; acute attacks decreased on average 4% per annum. New gout cases and acute attacks combined into 4-weekly incidence rates peaked during the "summer'' period of each year. There was an increased risk of gout diagnosis during summer months ( late April to mid-September; odds ratio 1.22, 95% CI 1.18 to 1.26). The annual prevalence of gout in 2001-7 was 0.46%, with highest rates in men >= 75 years (2.57%). Estimated prevalence based on a DDD of 400 mg allopurinol was 0.37%. Conclusion: The incidence of gout is seasonal. This has implications for the management of patients who currently have gout, and for those who are at risk of future attacks. The decreasing trend in the incidence of acute attacks suggests that patient management is improving.