BMI as a predictor of progression from TB infection to active TB in PLHIV.

Low body mass index (BMI) is a globally important risk factor for TB progression. Little is known about this association in people living with HIV (PLHIV) and the functional form of the BMI-TB incidence curve.Secondary analysis of a randomised controlled trial of TB preventive therapy among PLHIV in South Africa, Mozambique, and Ethiopia. Participants received 3 months of weekly high-dose rifapentine-isoniazid given once or twice over a period of 2 years. Multivariable fractional polynomials (MFPs) were used to investigate functional forms of BMI. Time to incident TB was modelled using Cox's proportional hazard regression.A total of 76 TB events were documented, giving an overall TB incidence rate of 1.2 per 100 person-years (95%CI 1.0-1.6). Baseline BMI <18.5 kg/m² was associated with a 2.6-fold increased hazard of TB compared with BMI 18.5-24.9 kg/m² (aHR 2.6, 95% CI 1.4-4.8, P < 0.001). BMI ≥30 kg/m² was associated with a lower hazard of TB (aHR 0.5, 95% CI 0.2-1.0). Continuous and categorical BMI showed weak evidence of quadratic dose-response relationships (P = 0.08 and P = 0.09, respectively). MFP analysis was consistent with a decline in TB incidence for increasing BMI to around 25 kg/m², followed by a less steep decline in TB incidence for increasing BMI >25 kg/m².In PLHIV, BMI showed an inverse log-linear association with TB incidence. The MFP approach showed that the relationship is more complex than a simple log-linear association..