Incidence of Lyme neuroborreliosis in Denmark: Exploring observed trends using public surveillance data, 2015–2019

Abstract

Lyme neuroborreliosis (LNB) can be a serious manifestation of Lyme borreliosis. We describe the incidence, time trends and geographic distribution of LNB in Denmark.We obtained LNB cases reported by laboratories and physicians (2015–2019) from the online platform maintained by the Statens Serum Institut (SSI) (2021b). The LNB incidence (per 100,000 persons) was calculated by dividing LNB cases by the population data (denominator) obtained from Statistics Denmark (2021).Between 2015 and 2019, laboratories reported annually 162 to 200 LNB cases, while physicians reported 48 to 68 cases. The annual LNB incidence notified by laboratories ranged from 2.8 (95% CI: 2.4‒3.3) to 3.4 (95% CI: 3.0‒4.0) per 100,000 persons for the 5 study years. The average annual LNB incidence per 100,000 persons for 5 Danish regions ranged from 2.3 to 3.3; for 11 provinces, from 1.9 to 7.6; and for 98 municipalities, from 0 to 22.1. Incidence peaks occurred in persons 5‒14 and 65‒74 years of age. Higher incidences were observed among males versus females in all age groups. LNB cases were reported throughout the year, with peaks in July to September.Notified LNB incidence in Denmark was moderate with no evidence of decline. Cases occurred across all regions but were focally concentrated among residents of some municipalities. Expanding the current surveillance system to include other manifestations of LB would be valuable to better understand geographic endemicity to inform targeted preventive measures.