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Risk factors for incident tuberculosis six months or more after ART initiation -experience from Johannesburg, South Africa
A. Van Rie1, D. Westreich1, I. Sanne2
1UNC-Chapel Hill Epidemiology, Chapel Hill, United States, 2Clinical HIV Research Unit, Department of Medicine, University of the Witwatersrand and Right to Care, Johannesburg, South Africa
Background: Tuberculosis (TB) in patients on antiretroviral treatment (ART) challenges the success of ART programs in sub-Saharan Africa and contributes to nosocomial transmission of TB in busy clinics. Risk factors for incident TB remain poorly characterized in developing world populations, especially after the first months of ART.
Methods: We analyzed prospective data from the Themba Lethu Clinic, Johannesburg, South Africa. Risk factors for late incident TB (TB six months or more after HAART initiation) were analyzed using Cox proportional hazards models. Models controlled for baseline history of TB, age, gender, employment status, pregnancy status, hemoglobin, and both baseline and time-updated (current) CD4 counts and body mass index (BMI).
Results: 5934 adults initiated ART between 1 April 2004 and 31 March 2007 and remained in care for at least six months; of those, 4% (n=217) developed TB after six months. Median time to TB was 418 days (IQR: 276-672), and incidence of TB was 2.3 cases per 100 person years (95% CI 2.0-2.7), four times lower than the incidence in the first six months of ART.
Risk of late incident TB increased sharply among those with current BMI< 18.5 (HR=6.52, 95% CI 3.60-11.80 compared to ≥25) and decreased sharply with higher current CD4 count (compared to CD4≤50, HR=0.84, 0.45, and 0.34 for CD4 51-100, 101-200, and 201-350). Risk increased with history of TB treatment (HR=1.50, 95% CI 1.09-2.50) and current viral load >10000 copies/ml (HR=2.44, 95% CI 1.57-3.79). Gender was not a risk factor for late incident TB.
Risk of late TB fell among those who were most sick (BMI< 25 and CD4≤100) at baseline, possibly due to selection bias.
Conclusions: Risk of TB six months or more after HAART initiation is associated with markers of poor response to HAART, including low CD4 count, low BMI, and poor viral response to HAART.
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