Lyme disease is a bacterial illness that is spread to humans by ticks. In early disease, around 6 in 10 people develop a rash that is specific to Lyme disease. This is commonly known as a bullseye rash. In England, the disease can sometimes be diagnosed clinically within the primary health care setting; if not, blood tests are needed for diagnosis. The official figures for the number of people diagnosed with Lyme disease are based on laboratory-confirmed cases from the national reference laboratory run by UKHSA. Previous work has suggested that for every case diagnosed at this laboratory, there are 2.35 cases recorded within primary care. This figure is known as the multiplication factor and allows the overall number of people diagnosed with Lyme disease in England to be estimated.
We think that this multiplication factor may now be out of date. This is because the National Institute for Health and Care Excellence introduced new guidance in 2018. From 2018, patients who have the bullseye rash should be diagnosed within primary care. Patients no longer need their diagnosis confirmed by tests run by the national reference laboratory. As the multiplication factor is based on pre-2018 data, it may mean the estimated figure for the overall number of people diagnosed with Lyme disease in England is lower than it should be. We want to access the primary care data from January 2013 to December 2023 in CPRD to determine whether this multiplication factor needs to be updated.
Lyme disease is a zoonotic tick-borne disease caused by bacteria in the Borrelia burgdorferi sensu lato genospecies complex. It is not a notifiable disease in the UK. This means that official incidence figures for England are based on the number of laboratory-confirmed cases at the UK Health Security Agency (UKHSA) reference laboratory (Rare and Imported Pathogens Laboratory, RIPL). However, general practitioners can make a clinical diagnosis of Lyme disease, so the official incidence figures are known to underestimate the true incidence.
A previous study that analysed primary care data in The Health Improvement Network (THIN) from 1998 to 2016, found that for every laboratory-confirmed case there are 2.35 cases identified within a primary care setting. This number has been used by UKHSA as a multiplication factor to estimate the total number of annual acute cases of Lyme disease. It is suspected that this multiplication factor may now be out of date. One reason for this is the introduction in 2018 of national guidance for the diagnosis and management of Lyme disease by the National Institute for Health and Care Excellence (NICE). Post-2018, patients presenting with a pathognomonic erythema migrans rash should be diagnosed without laboratory-confirmation.
This CPRD dataset will allow us to look both pre-introduction of the updated NICE guidance (pre-2018) and post-introduction (post-2018) to test the hypothesis that the multiplication factor has altered significantly post-2018 by running time series analysis models and looking for a structural break or interruption in 2018. It is important that the true incidence of Lyme disease is reported accurately by UKHSA to allow us to improve action on public health through data.
• Number of patients diagnosed with Lyme disease and prescribed with appropriate antibiotics within primary care;
• Comparison of time series of primary care Lyme disease incidence numbers with a separate time series of laboratory-confirmed cases;
• Calculate whether the multiplication factor to apply to official laboratory-confirmed case data to estimate the overall incidence of Lyme disease in England has changed significantly post-2018.
Amanda Semper - Chief Investigator - UK Health Security Agency (UKHSA)
Janie Olver - Corresponding Applicant - UK Health Security Agency (UKHSA)
Roberto Vivancos - Collaborator - UK Health Security Agency (UKHSA)