Modelling tuberculosis control priorities: more of the same will not do

In The Lancet Global Health, Juan F Vesga and colleagues1Vesga JF Hallett TB Reid MJA et al.Assessing tuberculosis control priorities in high-burden settings: a modelling approach.Lancet Glob Health. 2019; 7: e585-e595Summary Full Text Full Text PDF PubMed Scopus (36) Google Scholar reported on their assessment of tuberculosis control priorities in high-burden settings using a robust and well accepted modelling approach with a focus on what can be achieved by strengthening the tuberculosis cascade of care. The authors concluded that closing gaps and decreasing delays in the cascade of care will be valuable for improving patient outcomes and identifying programmatic priorities, and although their results were robust, their assumptions on the extent of reductions in gaps in the cascade of care were unrealistic. Their findings show that strengthening the tuberculosis cascade of care will be insufficient to achieve the End TB Strategy targets within this generation or the next, regardless of whether the challenges are a dysfunctional private sector, HIV coinfection, or multi-drug-resistant tuberculosis. The validity of modelling findings is entirely dependent on the robustness of the underlying assumptions,2Wejse C Xpert MTB/RIF is cost-effective, but less so than expected.Lancet Glob Health. 2019; 7: e692-e693Summary Full Text Full Text PDF PubMed Scopus (2) Google Scholar but Vesga and colleagues assumed that a sequence of gaps in the tuberculosis cascade of care can all be reduced to 5% and delays shortened by 25%. Although the assumed shortening of delays might be possible, reducing all cascade gaps to 5% would be extremely challenging. We are not aware of any published literature on any programme that was able to achieve these improvements, other than the accompanying Comment by Riitta A Dlodlo and Einar Heldal3Dlodlo RA Heldal E Comprehensive care for all individuals with tuberculosis is needed now.Lancet Glob Health. 2019; 7: e536-e537Summary Full Text Full Text PDF PubMed Scopus (3) Google Scholar stating it should be feasible. Nevertheless, modelling such extreme improvements can provide some clarity. Let us say that all gaps could be reduced to 5% even in the low-resource high-incidence settings in focus in the Article, what outcomes can be achieved? Reductions in the incidence of tuberculosis incidence of 27–38% by 2035 were predicted, and mortality reductions of 52–77%, with pre-elimination targets met by around 2100.1Vesga JF Hallett TB Reid MJA et al.Assessing tuberculosis control priorities in high-burden settings: a modelling approach.Lancet Glob Health. 2019; 7: e585-e595Summary Full Text Full Text PDF PubMed Scopus (36) Google Scholar Similarly modest improvements in disease burden in Fiji have been predicted with a set of interventions intended to capture a realistic scenario.4Ragonnet R Underwood F Doan T Rafai E Trauer J McBryde E Strategic planning for tuberculosis control in the Republic of Fiji.Trop Med Infect Dis. 2019; 4: e71Crossref PubMed Scopus (5) Google Scholar So although the current modelling study is impressive in showing the valuable effect of strengthening the tuberculosis cascade of care, the proper interpretation must be that an exclusive focus on the tuberculosis cascade of care is likely to be inadequate, and does not hold great promise for reducing tuberculosis burden, even if extremely comprehensive interventions are applied. Instead, we believe perspectives should be expanded to the entire cascade of tuberculosis pathogenesis, including the possibilities of breaking the transmission cycle between the points of transmission and reactivation with preventive interventions, which holds great promise for reducing tuberculosis burden.5Churchyard GJ Swindells S Controlling latent TB tuberculosis infection in high-burden countries: a neglected strategy to end TB.PLoS Med. 2019; 16e1002787Crossref PubMed Scopus (21) Google Scholar In particular, previous modelling suggested that preventive treatment would remain efficient in high transmission settings, where it is doubtlessly most needed.6Ragonnet R Trauer JM McBryde ES et al.Is IPT more effective in high-burden settings? Modelling the effect of tuberculosis incidence on IPT impact.Int J Tuberc Lung Dis. 2017; 21: 60-66Crossref PubMed Scopus (14) Google Scholar We declare no competing interests. Assessing tuberculosis control priorities in high-burden settings: a modelling approachLinked to transmission, the care cascade can be valuable, not only for improving patient outcomes but also in identifying and monitoring programmatic priorities to reduce tuberculosis incidence and mortality. Full-Text PDF Open AccessModelling tuberculosis control priorities: more of the same will not do – Authors’ replyThe tuberculosis care cascade is only one part of a much broader picture of tuberculosis control, a picture that involves prevention as well as cure, underpinned by a broader understanding of the determinants of tuberculosis.1 We thank Christian Wejse and colleagues for their Correspondence, and they raise an important point about the key role that tuberculosis prevention will need to play in tuberculosis control. We agree with their point, although the focus of our work is on the care cascade. Indeed, supplementary results in the appendix show how the care cascade alone will not be sufficient to eliminate tuberculosis as a public health problem. Full-Text PDF Open Access