Risk of hematologic cancers among individuals tested for Borrelia burgdorferi antibodies, and Borrelia burgdorferi seropositive individuals, a nationwide population-based matched cohort study

In a nationwide, matched cohort study, we aimed to investigate risks of hematologic cancers among individuals tested for Borrelia burgdorferi (Bb) antibodies, and among serum Bb seropositive individuals.We identified all Bb seropositive individuals in Denmark (1993-2020) (n=52,200) and constructed two age and sex-matched comparison cohorts: 1) Bb seronegative controls (n=104,400) and 2) background population controls (n=261,000). We calculated short-term odds ratios (aOR) (<1 month of study inclusion), and long-term hazard ratios (aHR) (>1 month after study inclusion) adjusted for age and sex. We stratified seropositive individuals on only Bb-IgM seropositive (n=26,103), only Bb-IgG seropositive (n=18,698), and Bb-IgM-and-IgG seropositive (n=7,399).Compared with the background population i ndividuals tested for Bb antibodies had increased short-term (aOR: 12.6, 95% CI: 10.1-15.6), and long-term (aHR: 1.3, 95% CI: 1.2-1.4) risk of hematologic cancers. The Bb seropositive individuals had no increased risk of hematologic cancers compared with those who tested negative for Bb, except that Bb-IgM-and-IgG seropositive individuals had increased long-term risk of chronic lymphatic leukemia (CLL) (aHR: 2.0, 95% CI: 1.2-3.4).Our results suggests that Bb antibody testing is included in the work-up of unspecific symptoms preceding diagnosis of hematologic cancers. Bb-IgM-and-IgG seropositivity was associated with a two-fold increased long-term risk of CLL, which warrants further investigation.