Prevalence of Tick-borne Neoehrlichia mikurensis in Individuals Undergoing B-cell Depleting Therapy in Denmark: A Prospective Cohort Study 2023-2024

BACKGROUND: Neoehrlichia mikurensis is an emerging tick-borne pathogen posing a particular risk to individuals undergoing B-cell depleting therapy (BCDT).

OBJECTIVE: To establish a rational testing strategy for N. mikurensis among individuals on BCDT METHODS: We conducted a prospective cohort study between January 2023 and December 2024 on Adults receiving BCDT, in the Capital Region of Denmark. A digital questionnaire covered tick exposure and symptoms. Blood was tested for N. mikurensis DNA by real-time PCR.

RESULTS: Of 1,211 eligible individuals, 443 (37%) were enrolled. The median age was 54 years, and 62% were female. PCR testing was performed on 389 participants, detecting N. mikurensis DNA in 1.0% (4/389; 95% CI: 0.4-2.6). All infected individuals reported prolonged symptoms (e.g., fatigue, fever, unintended weight loss) and responded rapidly to doxycycline therapy. Notably, only one of the four cases exhibited elevated CRP. Symptom-based screening yielded a high likelihood ratio of 25 for identifying positive cases.

CONCLUSIONS: Our results indicate that employing a symptom-based testing strategy for N. mikurensis is a rational approach for individuals undergoing BCDT.