Outcomes of Patients with Positive Latent Tuberculosis Screening in the San Antonio Military Health System

INTRODUCTION: Latent tuberculosis infection (LTBI) screening plays a vital role in global efforts to eliminate tuberculosis (TB). While LTBI treatment has been associated with lower rates of reactivation of TB and all military branches screening programs for LTBI screening, there is limited military data on factors associated with screening positivity and treatment completion.

MATERIALS AND METHODS: This retrospective study examined positive Quantiferon-Plus (QFT-Plus) assays in the San Antonio Military Health System between January 2022 and June 2024. Electronic medical records were reviewed for information, including demographics, indications for testing, TB risk factors, deployment and travel history, quantitative QFT-Plus results, final diagnosis, and treatment course. QFT-Plus assays were considered false positive in patients with repeat tests that were negative.

RESULTS: A total of 6,321 QFT-Plus assays were performed in the study period with 192 (3%) unique patients identified to have positive QFT-Plus assays. Ninety-seven (51%) patients were ultimately diagnosed with LTBI with most patients being active-duty military. The most common indication for testing was occupational screening, such as for health care workers. Patients with an initial greater TB-nil value were more likely to have true disease rather than a false positive (0.968 [0.52-3.5] vs. 0.435 [0.38-0.62], P = .0007). Of patients diagnosed with LTBI, a total of 58 (60%) initiated treatment and 41 (42%) had documented completion of treatment. Factors associated with incomplete treatment were use of an isoniazid-only regimen (n = 6, 60% non-completion rate) and reassignment to a new duty station after LTBI diagnosis (n = 11, 79% non-completion rate).

CONCLUSIONS: This study offers a modern evaluation of LTBI screening in a military setting and provides targets for future interventions including those who change duty stations or use an isoniazid-based regimen. Military clinicians should be aware that patients with a low positive TB-nil on QFT-Plus assays are frequently false positive and require repeat testing.