Social Vulnerability Modifies the Effects of Geographic Proximity on Engagement in Latent Tuberculosis Infection Care in a United States Safety Net Healthcare Network.

Background: Latent tuberculosis (TB) infection care often requires engagement with multiple teams in several locations throughout the diagnostic and treatment steps of the TB infection care cascade. The intersecting effects of geographic proximity and social drivers on care cascade retention have not been well examined. Methods: We conducted a retrospective cohort study of patients with a positive TB infection test between 2018-2019 within a health system in Boston, Massachusetts. The primary outcome was attendance at a TB clinic after a referral was placed. The primary exposure was geographic proximity, as measured by travel time by car. We assessed effect modification of proximity by Social Vulnerability Index (SVI), a composite measure of census tract social drivers. Results: We identified 1677 patients with positive TB infection tests; 1208 (72%) were referred to a TB clinic, of whom 748 (62%) completed referral. Longer travel times were associated with lower odds of referral completion (furthest vs nearest quartiles: adjusted odds ratio, 0.76 [95% confidence interval, .71-.82]). SVI significantly modified the effects of proximity: Increasing travel time was associated with decreasing probability of clinic attendance for patients in lower-vulnerability census tracts but had minimal effect on clinic attendance among patients in higher vulnerability census tracts. Conclusions: Additional support is needed for individuals referred to TB clinics that require long travel times to attend. Support should also account for other social drivers affecting care access for those living near TB clinics.