Combining primary care surveillance and a meta-analysis to estimate the incidence of the clinical manifestations of Lyme borreliosis in Belgium, 2015-2017.

Lyme borreliosis (LB) is an important tick-borne disease which can cause a broad range of symptoms mainly affecting the skin, the nervous system and the joints. This study aims to estimate the incidence of the different clinical manifestations of LB in Belgium. The incidence of erythema migrans (EM) was estimated through the network of sentinel general practices at 97.6/100,000 inhabitants (uncertainty interval [UI] 82.0-113.0) for the period 2015-2017. This result was used to estimate the incidence of other LB manifestations based on their proportional distribution (ratios) to EM reported in the neighboring countries of Belgium. To estimate these ratios, we performed a systematic review of studies published between February 1, 2008 and January 31, 2018 and pooled the results using a random effects meta-analysis. Six studies were retained in the systematic review, and the meta-analysis estimated the occurrence ratios for Lyme neuroborreliosis/EM, Lyme arthritis/EM and other manifestations/EM at 0.024 (95% confidence interval [CI] 0.016-0.037), 0.022 (95% CI 0.020-0.024) and 0.014 (95% CI 0.012-0.016) respectively. Applying these ratios to the EM incidence in Belgium resulted in an incidence estimation of 2.4/100,000 inhabitants (95% UI 1.5-3.7) for Lyme neuroborreliosis, 2.1/100,000 (95% UI 1.7-2.6) for Lyme arthritis and 1.4/100,000 (95% UI 1.1-1.7) for other less frequent manifestations. Some of these LB manifestations, other than EM, are more severe, hence these estimates are essential to assess the health burden and economic cost of LB which would be highly relevant for patients, healthcare providers and policymakers. As both over- and underestimation of different clinical LB manifestations remain possible due to characteristics of the primary surveillance systems and the disease itself, future studies to validate these estimates would be of great value.