The geographical distribution of tick bites and erythema migrans in general practice in The Netherlands.

BACKGROUND Lyme disease is caused by Borrelia burgdorferi which is transmitted in Europe by the tick ixodes ricinus. Erythema migrans is a skin lesion which is pathognomonic of Lyme disease. A retrospective study was carried out to determine the geographical distribution of the occurrence of tick bites and erythema migrans in the Netherlands and to identify ecological risk factors. METHODS In April 1995, all general practitioners (GPs) in the Netherlands were asked to complete a postal questionnaire on the number of tick bites and erythema migrans case-patients seen in 1994 and the size of the practice. Reminders were sent to non-responders. Information on ecological risk factors by local government area was obtained from a geographical information system. RESULTS The response rate was 79.9%. In 1994, GPs reported seeing approximately 33,000 patients with tick bites and 6500 with erythema migrans. The incidence rate of erythema migrans was estimated at 4.3 per 10,000 population. Ecological risk factors for both tick bites and erythema migrans were the proportion of the area covered by woods, sandy soil, dry uncultivated land, the number of tourist-nights per inhabitant and sheep population density. The cattle population density was a risk factor for erythema migrans. CONCLUSIONS Using simple methods, a crude estimate of the incidence rate of erythema migrans was obtained rapidly, and high risk areas were identified. Lyme disease appears to be an important problem in the Netherlands.