Neoehrlichia mikurensis infection associated with lymphoma or mimicking lymphoma in two cohorts of Swedish patients

The tick-borne bacterium Neoehrlichia (N.) mikurensis causes latent infections that can become symptomatic when B-cell defenses are compromised. We investigated the prevalence of N. mikurensis in two cohorts of Swedish patients: a prospective cohort (n = 186) evaluated for lymphoma and a retrospective cohort (n = 198) diagnosed with seven lymphomas. Samples were tested for N. mikurensis by PCR. Nine of 116 patients (7.8%) diagnosed with lymphoma in the prospective cohort, and 7/198 (3.5%) in the retrospective cohort had a concomitant N. mikurensis infection. Indolent lymphomas, particularly marginal zone lymphoma (9.3%), were frequently coupled with N. mikurensis infection. Males had higher risk of having lymphoma and N. mikurensis infection. N. mikurensis was diagnosed in 3.2% of patients without lymphoma, making it the most common infectious differential diagnosis for possible lymphoma. This emerging pathogen should therefore be considered as a differential diagnosis for patients with suspected lymphoma in N. mikurensis-endemic regions.