Prospects for Tuberculosis Elimination in the United States: Results of a Transmission Dynamic Model

Abstract

We estimated long-term tuberculosis (TB) trends in the US population and assessed prospects for TB elimination. We used a detailed simulation model allowing for changes in TB transmission, immigration, and other TB risk determinants. Five hypothetical scenarios were evaluated from 2017 to 2100: 1) maintain current TB prevention and treatment activities (base case); 2) provision of latent TB infection testing and treatment for new legal immigrants; 3) increased uptake of latent TB infection screening and treatment among high-risk populations, including a 3-month isoniazid-rifapentine regimen; 4) improved TB case detection; and 5) improved TB treatment quality. Under the base case, we estimate that by 2050, TB incidence will decline to 14 cases per million, a 52% (95% posterior interval (PI): 35, 67) reduction from 2016, and 82% (95% posterior interval: 78, 86) of incident TB will be among persons born outside of the United States. Intensified TB control could reduce incidence by 77% (95% posterior interval: 66, 85) by 2050. We predict TB may be eliminated in US-born but not non-US-born persons by 2100. Results were sensitive to numbers of people entering the United States with latent or active TB, and were robust to alternative interpretations of epidemiologic evidence. TB elimination in the United States remains a distant goal; however, strengthening TB prevention and treatment could produce important health benefits.

Figure 1.

Schematic of tuberculosis simulation model. The schematic shows compartments within each dimension of the model. A) Core TB dimension. B) TB drug-resistance dimension. C) HIV dimension. D) TB treatment history dimension. E) Risk group dimension. F) Age group dimension. Arrows identify entries to the model and possible transitions between compartments. Solid arrows indicate state transitions, dotted arrows indicate model entry for US-born individuals, and dashed arrows indicate model entry for non–US-born individuals. Non–US-born individuals enter distributed across all drug-resistance and age compartments (not shown). Exits due to death are not shown. ART, antiretroviral therapy; CD4, CD4 cell count per cubic millimeter of blood; INH, isoniazid; LTBI, latent tuberculosis infection; MDR-TB, multidrug-resistant tuberculosis; RIF, rifampicin; TB, tuberculosis; XDR-TB, extremely drug-resistant tuberculosis.

Figure 2.

Comparison of model estimates and data describing recent TB outcomes: TB cases, drug-resistance patterns, LTBI prevalence, and death due to TB. Figure panels present data and estimates for 1995 to the most recent year available. Model results are plotted for 100 calibrated parameter sets to represent uncertainty in modeled results. TB case data were drawn from the routine TB case reporting system. The calibration target for human immunodeficiency virus–positive TB cases was adjusted to allow for incomplete reporting in early years. Calibration targets for LTBI prevalence estimates were derived from IGRA results from the National Health and Nutrition Examination Survey 2011–2012 (13). The calibration target for TB-related deaths represents reports of TB (International Statistical Classification of Diseases and Related Health Problems, 10th Revision, codes A16–19) included in multiple cause of death reports. IGRA, interferon-γ release assay; INH, isoniazid; LTBI, latent tuberculosis infection; MDR-TB, multidrug-resistant tuberculosis; TB, tuberculosis.

Figure 3.

Historical and projected trends in TB cases in the United States with current prevention and treatment activities, stratified by nativity, 2000–2100. Bold solid lines represent the best estimate projection (posterior mean from Bayesian evidence synthesis) for a given population group and projection year. Faint solid lines represent results from 100 individual, calibrated parameter sets, representing uncertainty in modeled results. Dashed line represents the fraction of TB cases in each year among non–US-born persons. Horizontal dotted line represents the US TB elimination target (<1 annual TB cases per million). TB, tuberculosis.

Figure 4.

Projected trends in tuberculosis outcomes under modeled scenarios, 2015–2050. Lines represent best estimate projection (posterior mean from Bayesian evidence synthesis) for a given population group, scenario, and projection year. A) New M. tuberculosis infections per million. B) LTBI prevalence. C) Number of reported TB cases per million. D)Prevalence of MDR-TB among new TB cases. E) Number of TB deaths per million. LTBI, latent tuberculosis infection; MDR-TB, multidrug-resistant tuberculosis; TB, tuberculosis; TLTBI, treatment of latent tuberculosis infection.