Lyme disease (Lyme borreliosis) is a tick-borne infectious disease. It is caused by different genospecies of Borrelia including B. burgdorferi sensu strictu (ss), B. afzelii and B. garinii, which can be transmitted to humans through a bite from an infected tick. Infection is more likely the longer a tick is attached to the skin. Ticks live in grassy and wooded areas, both in rural and urban locations. People who spend time in these areas for work or recreation are at increased risk of tick exposure.

Lyme disease can occur anywhere in the UK, although some areas have a higher reported incidence. Approximately 50% of laboratory-confirmed cases are diagnosed in the South East and South West of England. High incidence is also reported in Scotland. Worldwide, Lyme disease occurs mainly in the northern hemisphere, and travellers to areas of Europe, North America and elsewhere may be at risk. However, the true incidence of Lyme disease is unknown.

Although the disease has been recognised in mainland Europe for more than a century, it was first reported in England and Wales in the 1980s. Public Health England (PHE) reports that there are approximately 1,000 serologically confirmed cases of Lyme disease each year in England and Wales. Many diagnoses will also be made clinically without laboratory testing. The true number of cases is currently unknown.

In England and Wales, cases of laboratory-confirmed Lyme disease have increased. It is not certain how much of the rise is due to increased awareness and how much to the spread of the disease.

Infection with B. burgdorferisensu lato (sl) can sometimes go unremarked, with mild symptoms that are ignored by the person. When symptoms occur, this is called Lyme disease. Many people may not notice or remember a tick bite. A bite can be followed by an 'erythema migrans' rash, which is sometimes mistaken for cellulitis or ringworm, and effective treatment is delayed. If there is no erythema migrans or it is unnoticed, diagnosis can be difficult because the same symptoms may be caused by many other conditions as well as Lyme disease.

The terminology around Lyme disease is varied and many poorly defined terms are used in the literature (such as chronic Lyme disease and post-Lyme disease). This guideline has avoided using controversial definitions and has concentrated on providing advice on diagnosis and treatment based on the available evidence, according to the clinical context, presentation, symptoms and available treatments. The guideline committee has noted the poor-quality evidence available on both diagnosis and treatment.

The guideline aims to raise awareness of when Lyme disease should be suspected and to ensure that people with suspected Lyme disease are given early and consistent treatment. The guideline committee has also developed a series of research recommendations to improve basic epidemiology, understanding of the natural history of Lyme disease, and to develop diagnostic tests appropriate for UK infections.