In sub-Saharan Africa, a significant portion of the large latent TB reservoir is established outside of the home. Data on TB risk among mobile children and adults who travel outside of the community for work or school is limited, but critical to targeting TB prevention efforts.
We assessed the association between mobility and incident TB infection in an ongoing longitudinal cohort of tuberculin skin test (TST) negative children (≥5 years) and adults in the SEARCH trial (NCT:01864603) in Eastern Uganda, this sample was enriched for HIV-infection. Participants were included in the TST negative cohort if they had no induration at their baseline TST. A follow-up TST was placed one year from baseline. Incident TB infection was defined as a change in TST induration from 0mm at baseline to ≥10mm at their annual follow up test. Mobility was defined as living outside of the community for more than 1 month in the last year, such as to attend boarding school or work. We used multivariate logistic regression and adjusted for confounding by age, gender, lowest wealth tertile, BCG vaccination, HIV status, living in household with HIV-infected adult, and household TB contact within the last year.
One year follow-up TSTs were completed in 739 participants (age ≥5 years) from the TST negative cohort. Our definition of incident TB infection was met by 89 (12%) participants. Among those with incident TB infection: 48% were ages 5-14 years of age, 17% were 15-24 years, and 35% were older than 25 years, 65% were women, 93% had a BCG scar or record of vaccination, 10% were mobile, 6% reported a household contact within a year. In the adjusted model, mobility was associated with a 2.6-fold increased odds of incident TB infection (95% CI: 1.3-7.5, p<0.01). Reporting a household contact was also independently associated with TB infection (aOR 11.3, 95% CI: 2.1-62.2, p<0.01). HIV infection and living in a household with one or more HIV-infected adult was not associated with incident TB infection.
In a rural Ugandan cohort of children and adults where population based treatment of HIV is ongoing, mobility was a predictor of increased risk of incident TB infection. TB exposure outside of the community, such as in boarding schools, may drive a portion of TB infections in rural communities. Casual TB contacts within rural communities and undiagnosed household contacts may explain the incident infections not associated with a known household contacts or mobility.