Background: Patients with a compromised immune system are at risk for converting from latent tuberculosis infection (LTBI) to active tuberculosis infection. Multiple sclerosis (MS) therapies may put individuals with LTBI at higher risk of developing tuberculosis.

Methods: Patients of the Beth Israel Deaconess Medical Center MS Center were screened for tuberculosis as part of routine testing with the QuantiFERON-TB Gold In-Tube (QFT-GIT) assay from 2013 to 2017. Patients were tested either prior to or while on immunomodulating therapy.

Results: 4 out of 222 patients (1.8%, 95% CI 0.1-3.6%) had positive QFT-GIT testing; 3 patients had risk factors for tuberculosis, having emigrated from TB endemic countries or worked in the health care industry. 28 out of 222 patients (12.6%) had an indeterminate assay result and 75.0% of these occurred in patients taking dimethyl fumarate (DMF). Fingolimod, natalizumab, or anti-CD20 treatments showed 0-7.7% indeterminate results.

Conclusions: LTBI was seen at 1.8% prevalence in the Beth Israel Deaconess MS Center. Not all LTBI cases were associated with known risk factors for tuberculosis. Screening for LTBI prior to starting immunosuppressive agents for MS could help prevent activation of tuberculosis. DMF use is associated with indeterminate results in the QFT-GIT assay, possibly due to functional effects on lymphocytes and levels of cytokines, like interferon gamma. In contrast, fingolimod use was rarely associated with indeterminate QFT-GIT results in spite of a high rate of lymphopenia in virtually all cases.

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