Continuing increase of tick bites and Lyme disease between 1994 and 2009

Nationwide cross-sectional retrospective studies have shown a continuous increase in general practitioner (GP) consultations for tick bites and diagnoses of erythema migrans between 1994 and 2005 in the Netherlands. In this paper, we report incidence estimates for GP consultations for tick bites and erythema migrans diagnoses in 2009, and we compare the observed increase in GP consultations to reports of tick bites in two retrospective cross-sectional surveys of the general population.

All GPs in the Netherlands were asked to complete a postal questionnaire on the number of consultations for tick bites and erythema migrans diagnoses in 2009, and the size of their practice populations. To investigate how the incidence of GP consultation rates for tick bites and erythema migrans relate to the incidence of tick bites in the general population, questionnaire data on tick bites were analyzed from two large population surveys conducted to evaluate the national immunization program in 1995/1996 and 2006/2007.

The 2009 GP survey revealed a further increase, to 564 tick bite consultations per 100,000 inhabitants, and 134 erythema migrans diagnoses per 100,000 inhabitants of the Netherlands. The two population surveys from 1995/1996 and 2006/2007 exhibited an almost twofold increase of the incidence of tick bites in the general population from 4099 per 100,000 population in 1996, to 7198 per 100,000 population in 2007. People nationwide noticed approximately 1.1 million tick bites in 2007.

Our observation of increases in GP consultations for tick bites and erythema migrans diagnoses between 1994 and 2009 are confirmed by the parallel increase of tick bites reported by the general population, although consultation rates slightly increased. For every sixty tick bites in the general population in 2007, we observed one GP consult for erythema migrans. The increase in tick bites poses a progressive threat to public health.