<i>Neoehrlichia mikurensis</i> infection associated with lymphoma or mimicking lymphoma in two cohorts of Swedish patients

The tick-borne bacterium <i>Neoehrlichia</i> (<i>N.</i>) <i>mikurensis</i> causes latent infections that can become symptomatic when B-cell defenses are compromised. We investigated the prevalence of <i>N. mikurensis</i> in two cohorts of Swedish patients: a prospective cohort (<i>n</i> = 186) evaluated for lymphoma and a retrospective cohort (<i>n</i> = 198) diagnosed with seven lymphomas. Samples were tested for <i>N. mikurensis</i> 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 <i>N. mikurensis</i> infection. Indolent lymphomas, particularly marginal zone lymphoma (9.3%), were frequently coupled with <i>N. mikurensis</i> infection. Males had higher risk of having lymphoma and <i>N. mikurensis</i> infection. <i>N. mikurensis</i> 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 <i>N. mikurensis</i>-endemic regions.