Lyme borreliosis epidemiology and surveillance

Published 1 May 2013

0.1 Background

Lyme borreliosis (LB) is the most common vector-borne human infection in England and Wales. As elsewhere in northern Europe, the spirochaetes are transmitted by the hard bodied tick, Ixodes ricinus, commonly known as deer or sheep ticks. Habitats suitable for acquiring Borrelia burgdorferi infection occur in temperate regions of the northern hemisphere, usually in forested woodland or heathland areas which support the life-cycles of ticks and the small mammals and birds that are the reservoir hosts for B. burgdorferi. Several pathogenic genospecies of B. burgdorferi have been identified in Europe and there is evidence for some variation in the types of clinical presentation caused by these different genospecies.

Lyme borreliosis is monitored in England and Wales through passive and enhanced surveillance:

0.2 Passive surveillance

Cases of Lyme borreliosis are not statutorily notifiable by medical practitioners in England, Wales and Northern Ireland. However, since October 2010 under the Health Protection (Notification) Regulations 2010, every microbiology laboratory (including those in the private sector) in England is required to notify all laboratory diagnoses of borreliosis to the Health Protection Agency (now Public Health England). Previously, reporting by laboratories was on a voluntary basis.

0.3 Enhanced surveillance

This was introduced in late 1996 in order to improve reporting levels and to collect additional clinical and epidemiological information on cases. The Rare and Imported Pathogens Laboratory at PHE Porton provides national diagnostic services and will continue to report laboratory confirmed cases directly to the Zoonoses Surveillance Unit at Public Health Wales.

Between 1997 and 2003, questionnaires were sent to clinicians requesting additional data on laboratory-confirmed cases. This included age and sex, clinical features and tick exposure risk factors, and occupational and travel histories both within and without the UK. This strategy improved LB surveillance, achieving an 85% return rate in the first full year of enhanced surveillance. The data collected helped to enhance knowledge of LB in the United Kingdom.

Since August 2000, there has been a single laboratory in England and Wales offering a wide range of specialised tests for Lyme disease. This is now at PHE Porton. The availability of a single reference facility has long improved the completeness of reporting of laboratory confirmed cases. Before August 2000, several other laboratories also offered some specialised tests but did not report laboratory-confirmed cases. As a result, a significant number of laboratory-confirmed cases were not included in official statistics, resulting in significant under-reporting of cases prior to 2000.

0.4 Results

The data analysed in the following sections are for laboratory-confirmed cases of LB. Reporting levels have improved, but the data remain incomplete because they do not include cases diagnosed and treated on the basis of clinical features such as erythema migrans (the early rash of Lyme borreliosis), without laboratory tests. It is estimated that between 1,000 and 2,000 additional cases of LB occur each year in England and Wales.

0.5 Annual totals and rates

Since the introduction of enhanced surveillance in 1997, over 6,900 cases have been reported (Table 1). Mean annual incidence rates for laboratory-confirmed cases have risen from 0.38 per 100,000 total population for the period 1997-2000, to 0.64 in 2002, and to 1.64 cases per 100,000 total population in 2010.

0.6 Laboratory reports of Lyme borreliosis: England and Wales, annual totals and rates, 1997 to 2011.

Years Total reports received Mean annual range total Mean annual rate per 100,000 population
1997 to 2000 803 201 (148 to 322) 0.38
2001 268 268 0.50
2002 340 340 0.64
2003 292 292 0.55
2004 500 500 0.95
2005 595 595 1.10
2006 768 768 1.46
2007 797 797 1.46
2008 813 813 1.52
2009 863 863 1.59
2010 905 905 1.64
2011 959 959 1.73

Laboratory-confirmed reports of Lyme borreliosis have risen steadily since reporting began in 1986. Several factors have contributed to the increase: increased awareness of the disease, greater access to diagnostic facilities, more sensitive diagnostic methods, the introduction of the enhanced surveillance scheme in late 1996, and more complete reporting of cases since 2000. Other factors that may have contributed in part to the observed increase in LB include changes in population sizes and geographical ranges of I. ricinus ticks both in the UK and throughout Europe as a result of successive mild winters, increased recreational travel to high endemic areas, and the increasing popularity of activity holidays such as walking, trekking, and mountain biking in the UK and abroad. In recent years, migrants from central and eastern European countries (regions with high prevalence of Lyme borreliosis) have also contributed to higher incidence of infection identified (but not necessarily acquired) in the UK.

0.7 Age and sex

People of all ages and both sexes are equally susceptible. The highest attack rates occur in people aged between 45 and 64 years, followed by those aged from 24 to 44 years.

0.8 Occupationally-acquired cases

Occupationally acquired Lyme borreliosis is seldom reported. Most cases occur in forestry workers, farmers, deer handlers and gamekeepers. Occupationally-acquired cases should also be notified to the Health and Safety Executive (HSE), under the RIDDOR regulations.

0.9 Seasonality

Lyme borreliosis is more commonly diagnosed during the summer season, coinciding with tick activity, but cases are reported throughout the year. Nearly half of all cases have dates of specimen collection in July, August and September. Most of these probably acquired infection in late spring and early summer, allowing for the time period between being bitten, developing symptoms, and developing levels of antibodies high enough to give positive results in laboratory tests. This is also consistent with the peak tick feeding period of late spring and early summer.

0.10 Geographical distribution

Since 2000, an average 15% of cases are known to have been acquired abroad. The remaining cases are predominantly those acquired in the United Kingdom, but for some the travel history is not known. Cases have been reported from most counties in England and Wales, with infection occurring most frequently in Exmoor, the New Forest, the South Downs, parts of Wiltshire and Berkshire, Surrey and West Sussex,Thetford Forest, the Lake District and the North York Moors. Cases have been reported occasionally from many other areas with suitable tick habitats.

Of cases with a definite travel history, most have been acquired in the United States, France, Germany, Scandinavia and other northern and central European countries - and most occurred in holidaymakers. In recent years, there have been greater numbers of cases acquired in central and eastern Europe, reflecting increased tourism to and immigration from these areas.

0.11 Clinical presentations

Following an initial infection, which is localised to the site of the tick bite and commonly characterised by an expanding red rash (erythema migrans), the bacteria may spread to other site in the body. In the UK, the commonest secondary sites of infection with Lyme borreliosis are associated with the nervous system (neuroborreliosis). Clinical presentations include facial palsy, meningitis and radiculopathy (spinal nerve root inflammation) occurring within weeks or months of infection. Up to a third of cases in the UK may present with localised or general symptoms without evidence of a rash. Lyme arthritis is a rare complication of infections acquired in the UK, but is more common in patients who have been infected in North America or central Europe (Borrelia burgdorferi sensu stricto, the genospecies strongly associated with Lyme arthritis, is rare in the UK). Acrodermatitis chronica atrophicans (ACA), a skin condition caused by long-standing infection, which occurs in Scandinavia and central Europe, is seen occasionally in the UK.

Last reviewed: 2 May 2013