European countries have a wide variety of surveillance system (passive vs. mandatory and sentinel sites vs. national) for Lyme borreliosis, according to their public health structures. Clinical case definitions (clinical, laboratory, or both) and testing methods may also vary, limiting comparison across countries. Few countries have made Lyme borreliosis a compulsorily notifiable disease, mostly due to the wide range of clinical manifestations, to the absence of immediate human threat, and to the absence of human transmission. Some countries chose the voluntary notification through general practioners networks (sentinel surveillance system). In most countries, reporting is conducted through diagnostic laboratories reporting on the available details of patients with positive tests. There are several drawbacks involved in using such systems for the estimation of European Lyme borreliosis incidence, including under-reporting of EM, varying patterns of test referrals, varying serodiagnostic criteria and seropositivity linked to past exposure. Within these limitations it is possible to gain useful information from individual countries’ systems through year-to-year comparisons of within-country data.
Prospective clinically based studies yield the most accurate information on incidence. However, these are more costly in time and resources than indirect methods, which may represent the only means to carry out surveys in some areas. Indirect methods may include the measurement of the abundance of Ixodes ricinus ticks, the prevalence of B. burgdorferi-infected ticks and seroprevalence studies. All of these indirect measures have weaknesses as indicators of Lyme borreliosis, but at present human seroprevalence studies probably represent the best method to obtain epidemiological data throughout Europe. Taking the limitations of seroprevalence methods into account, it is clear that Lyme borreliosis shows a gradient of increasing incidence from west to east with the highest incidences in central-eastern Europe (Table 1), a gradient of decreasing incidence from south to north in Scandinavia and north to south in Italy, Spain and Greece has also been noted.

Table 1. Incidence per country according to the source of surveillance

Incidence (number of cases per 100,000 population per year, PPY)	Countries with LB incidence reported in the literature	Countries with LB reported by national system surveillance
>100/100,000 PPY	Belgium, Finland, the Netherlands, and Switzerland	Estonia, Lithuania, Slovenia, and Switzerland
40-80/100,000 PPY	–	France and Poland
20-40/100,000 PPY	Czech Republic, Germany and Poland	Finland and Latvia
<20/100,000 PPY	Belarus, Croatia, Denmark, England, France, Ireland, Portugal, Russia, Scotland, Slovakia, and Sweden	Belgium, Bulgaria, Croatia, England, Hungary, Ireland, Norway, Portugal, Romania, Russia, Scotland, and Serbia

Higher incidences are observed at the subnational level (up to 464/100,000 PPY in specific local areas).

References

Böhmer MM, Ens K, Böhm S, Heinzinger S, Fingerle V. Epidemiological Surveillance of Lyme Borreliosis in Bavaria, Germany, 2013-2020. Microorganisms. 2021;9(9):1872. doi: 10.3390/microorganisms9091872. PMID: 34576768; PMCID: PMC8467410.

Burn L, Vyse A, Pilz A, Tran TMP, Fletcher MA, Angulo FJ, Gessner BD, Moïsi JC, Stark JH. Incidence of Lyme Borreliosis in Europe: A Systematic Review (2005-2020). Vector Borne Zoonotic Dis. 2023;23(4):172-194. doi: 10.1089/vbz.2022.0070.

Burn L, Tran TMP, Pilz A, Vyse A, Fletcher MA, Angulo FJ, Gessner BD, Moïsi JC, Jodar L, Stark JH. Incidence of Lyme Borreliosis in Europe from National Surveillance Systems (2005-2020). Vector Borne Zoonotic Dis. 2023;23(4):156-171. doi: 10.1089/vbz.2022.0071.

Septfons A, Goronflot T, Jaulhac B, Roussel V, De Martino S, Guerreiro S, Launay T, Fournier L, De Valk H, Figoni J, Blanchon T, Couturier E. Epidemiology of Lyme borreliosis through two surveillance systems: the national Sentinelles GP network and the national hospital discharge database, France, 2005 to 2016. Euro Surveill. 2019;24(11):1800134. doi: 10.2807/1560-7917.ES.2019.24.11.1800134.

Sykes RA, Makiello P. An estimate of Lyme borreliosis incidence in Western Europe†. J Public Health (Oxf). 2017;39(1):74-81. doi: 10.1093/pubmed/fdw017.