Trends in Lyme disease incidence in England, 2013 to 2024

Official Lyme disease incidence figures for England are based on the number of cases with a laboratory-confirmed diagnosis from the national reference laboratory. However, these figures underestimate the true incidence of acute cases since patients can also be diagnosed clinically without the need for laboratory testing. The use of a multiplication factor has been proposed to estimate total Lyme disease incidence from the number of laboratory-confirmed cases. The current multiplication factor is derived from data spanning 1998 to 2016 and is thought to be outdated, in part due to the introduction of new national Lyme disease management guidance in 2018. The aim of this study was to analyse more recent laboratory and primary care data to identify trends in case numbers and to derive updated estimates of the total annual number of acute Lyme disease cases in England. Data spanning 2013 to 2024 from the national reference laboratory and a primary care data source were analysed using seasonal time series models. The presence of structural breaks was investigated using the PELT or BinSeg methods, and annual multiplication factors were estimated using a Poisson regression model. No substantial change was found in the number of laboratory-confirmed Lyme cases from 2013 to 2024 in England, whereas the number of cases diagnosed in primary care increased significantly over the same period, with an average of an additional 498 cases per year. This has increased our best estimate of the multiplication factor from 2.35 (95% confidence interval, 1.81 - 2.88) to 6.20 (6.17 - 6.24), which is the average for the years 2020 - 2024. Use of this updated multiplication factor should improve the accuracy of annual symptomatic Lyme disease case estimates for England.