Incidence of Lyme disease in the UK
By Dr. Victoria Cairns
Lyme disease (LD), also known as Lyme borreliosis, has become the most common tickborne infection in many parts of Europe and the USA. The US Centers for Disease Control and Prevention (CDC) estimate around 300 000 new cases of LD per year in the US based on the results of two studies.1 2 A WHO report stated that about 85 000 cases are reported annually in Europe with wide variability between and within countries, but they noted that many LD infections go unrecognised due to inconsistent and incomplete methods of ascertainment of LD.3 A more recent estimate was around 232 000 LD cases per year in Western Europe, although some countries included centralised reporting only.4 Numbers based on centralised reporting are likely to be considerable underestimates. The number of cases from centralised reporting to the US CDC is around one-tenth of what the CDC calculated based on estimates from other sources.5
The official estimate for the UK is around 2000–3000 new cases of LD per year based on laboratory data in England and Wales and centralised reporting in Scotland.6 The higher incidence rates seen in some neighbouring countries suggest a potential underestimation of the incidence rate and number of cases in the UK.4 The British National Institute for Health and Care Excellence (NICE) stresses the need for an epidemiological study on LD in the UK.7
To address the concern that LD may be currently underestimated in the UK, we used general practitioner (GP) records and conducted an epidemiological study to estimate the annual incidence rate and total number of cases of LD by geographic region.
Altogether 4083 cases of LD were detected among 4025 patients in the CPRD between 2001 and 2012. Only 56 of the 4025 patients (1.4%) appeared to have had more than one LD infection. Of those, 54 patients had exactly one LD reinfection and two had exactly two reinfections, that is, a total of 58 reinfections, based on our 365 day reinfection blocking-time-window.
Of the 4083 cases, 892 (21.8%) had a record of ECM, 1702 (41.7%) had ‘clinically diagnosed LD’, 1913 (46.9%) were in the category ‘treated suspected LD’ and 468 (11.5%) had ‘treated possible LD’ (figure 1 and table 1). Nearly one quarter of all cases were aged under 30, 53.2% were female and half of the diagnoses were made in the summer months. Of the 4083 cases, 3470 (85.0%) had a recording of a GP prescription for antibiotics at their first visit meeting the LD criteria. Of those treated 87.3% received doxycycline or amoxicillin (table 1). LD was detected in every region of the UK with the largest number of cases in Scotland followed by South Central and South West England (table 1 and figure 2). Among the 4083 LD cases detected in this study, 1677 (41.1%) had at least one recording of an LD laboratory test, with an average of 1.4 tests among those tested. Altogether 9045 LD laboratory tests were recorded in the CPRD during this time, which corresponds to an estimated 1 07 390 tests in those 12 years, ranging from 1356 tests in 2001 to 15 342 in 2012.
This is the first epidemiological study in the UK on the temporal trends of LD estimated from primary care data. The number of LD cases recorded by GPs increased rapidly over the years 2001– 2012, leading to an incidence rate of 12.1 per 100 000 persons per year and an estimated total for the UK of 7738 in 2012. The incidence rate was highest in Scotland, possibly due to the more moist environment suitable for ticks, the popularity of Scotland for walking and an increased awareness there of LD. This is followed by high rates in South West and South England, but LD was diagnosed in every region of the UK. From 2009 to 2012, the number of treated suspected cases continued to increase, unlike the number of clinically diagnosed LD cases, suggesting greater caution among the GPs and willingness to treat the illness early before confirming the diagnosis. Greater caution by GPs is reasonable as rapid treatment is important to avoid long-term problems. The NICE guideline states that symptoms of LD may take months or years to resolve even after treatment, and that some symptoms may be a consequence of permanent damage from infection. NICE writes that prompt antibiotic treatment reduces the risk of further symptoms developing and increases the chance of complete recovery.7 The increase in laboratory testing may be in part due to the increased awareness of LD as a result of the increased media coverage in recent years. However, a meta-analysis of studies looking at laboratory testing of LD showed relatively high rates of false negative laboratory results and false positive results, and the authors concluded that a negative result cannot be taken as evidence of lack of LD infection.
LD is seen in every region of the UK. Infected ticks can be transported by migrating birds,22 so patients can be infected with LD wherever the habitat is suitable for ticks that carry Borrelia.23 Furthermore, an estimated 15%–20% of laboratory-confirmed LD infections seen in the UK were caught abroad.6 The best defense against LD is through preventive measures such as avoiding dense vegetation particularly wooded or grassy areas with moist and humid environments, use of tick repellents and pesticides on skin and clothing, tucking trousers into socks and searching the body for ticks after potential exposure.24 Other sources of data will need to be explored for the incidence of LD in the UK since 2012 and in the future. LD mimics many other disorders and so inevitably some LD cases remain undiagnosed.
The incidence of LD in the UK is about threefold higher than previously estimated, and people are at risk throughout the UK. These results should lead to increased awareness of the need for preventive measures. Greater awareness of the risks may also lead to more rapid diagnosis and treatment which is important to prevent long-term morbidity.