Preventing tuberculosis with community-based care in an HIV-endemic setting: a modeling analysis

Abstract

Introduction: Antiretroviral therapy (ART) and TB preventive treatment (TPT) both prevent tuberculosis (TB) disease and deaths among people living with HIV. Differentiated care models, including community-based care, can increase uptake of ART and TPT to prevent TB in settings with a high burden of HIV-associated TB, particularly among men.

Methods: We developed a gender-stratified dynamic model of TB and HIV transmission and disease progression among 100,000 adults ages 15-59 in KwaZulu-Natal, South Africa. We drew model parameters from a community-based ART initiation and resupply trial in sub-Saharan Africa (Delivery Optimization for Antiretroviral Therapy, DO ART) and other scientific literature. We simulated the impacts of community-based ART and TPT care programs during 2018-2027, assuming that community-based ART and TPT care were scaled up to similar levels as in the DO ART trial (i.e., ART coverage increasing from 49% to 82% among men and from 69% to 83% among women) and sustained for ten years. We projected the number of TB cases, deaths, and disability-adjusted life years (DALYs) averted relative to standard, clinic-based care. We calculated program costs and incremental cost-effectiveness ratios from the provider perspective.

Results: If community-based ART care could be implemented with similar effectiveness to the DO ART trial, increased ART coverage could reduce TB incidence by 27.0% (range 21.3% - 34.1%) and TB mortality by 36.0% (range 26.9% - 43.8%) after ten years. Increasing both ART and TPT uptake through community-based ART with TPT care could reduce TB incidence by 29.7% (range 23.9% - 36.0%) and TB mortality by 36.0% (range 26.9% - 43.8%). Community-based ART with TPT care reduced gender disparities in TB mortality rates by reducing TB mortality among men by a projected 39.8% (range 32.2% - 46.3%) and by 30.9% (range 25.3% - 36.5%) among women. Over ten years, the mean cost per DALY averted by community-based ART with TPT care was $846 USD (range $709 - $1,012).

Conclusions: By substantially increasing coverage of ART and TPT, community-based care for people living with HIV could reduce TB incidence and mortality in settings with high burdens of HIV-associated TB and reduce TB gender disparities.

Keywords: Differentiated care; HIV epidemiology; TB; cost effectiveness; gender; modeling.

Figure 1.. Illustration of TB and HIV dynamic transmission model.

Rates of flow between each compartment are governed by differential equations, as described in the appendix. Although not visualized here, each TB and HIV compartment is stratified across two TB drug-resistance categories and two genders. The latent TB infection (LTBI) compartment is distinguished by those infected within two years, considered recent, and more than two years, considered remote. The rate of TB preventive treatment (TPT) and antiretroviral therapy (ART) initiations (highlighted in green) are directly impacted by care delivery programs (Table 2). ART coverage is used to calculate ART initiation rates so that the proportion of PLWH on ART by gender corresponds to ART coverage assumptions. The active TB compartment is highlighted in red to emphasize the compartment capturing incident TB.

Figure 2.. Estimated TB incidence and mortality by gender.

The mean, maximum, and minimum yearly TB incidence and mortality rates from 1990–2017 over the 859 accepted parameter sets are shown in grey (dots). The mean, maximum, and minimum yearly TB incidence and mortality rates during the intervention period (2018–2027) over the 859 accepted parameter sets are illustrated by care-delivery program. During the intervention period, Program 1 (standard facility-based ART and TPT care) is shown in blue (dots), Program 2 (community-based ART care with standard facility-based TPT care) is shown in green (stars), and Program 3 (community-based ART with TPT care) is shown in red (diamonds).

Figure 3:. Estimated TB incidence and mortality by care-delivery program.

The mean, maximum, and minimum yearly TB incidence and mortality rates are estimated over the 859 accepted parameter sets. Program 1 (standard facility-based ART and TPT care) is shown in blue (dots), Program 2 (community-based ART care with standard facility-based TPT care) is shown in green (stars), and Program 3 (community-based ART with TPT care) is shown in red (diamonds).

Figure 4:. Sensitivity analysis of the discounted incremental cost per DALY averted by community-based ART with TPT care (Program 3) versus standard facility-based ART and TPT care (Program 1) over the intervention period.

The solid line represents the mean discounted incremental cost per DALY averted over the 859 accepted parameter sets of $846 USD per DALY averted. The dashed vertical line represents the cost-effectiveness threshold of $590 USD per DALY averted. The horizontal bars represent the discounted incremental cost per DALY averted at bounds of 25% above of the modeled cost parameter (high) and 25% below the modeled cost parameter (low). All costs are in 2018 USD.