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Fig. 1 | BMC Medicine

Fig. 1

From: Prioritising attributes for tuberculosis preventive treatment regimens: a modelling analysis

Fig. 1

Schematic illustration of the model structure. For clarity, the figure concentrates on model compartments relevant to latent TB infection, its progression to active disease, and the effect of preventive treatment on these dynamics; further information on the care cascade for active TB disease (shown in the dotted rectangle) is provided in the supporting information. Each compartment shown here is further stratified by the HIV status. Amongst compartments relating to the natural history of TB, U denotes ‘uninfected’; L(f)denotes latent infection with ‘fast’ progression (in the first 2 years following infection); L(s) denotes latent infection with ‘slow’ progression; and I denotes active, infectious TB. The modelled action of preventive treatment is as follows: S denotes individuals who are bacteriologically cured of infection as a result of the regimen; the parameter c governs the proportion cured in this way. Q denotes individuals with non-curative, post-regimen protection; the parameter e denotes the strength of non-curative protection, while g denotes its post-regimen durability. P1 and P2 represent individuals who are, respectively, undergoing the first and second halves of the regimen. Reinfection is possible for stages P1, P2, S, Q, at a reduced rate compared to R, given an assumed level of protection from preventive therapy. Reinfection is not shown for clarity, but is modelled by transitions from P1, P2, Q and R to their respective f states (e.g., P1(f)), and from S to Lf. We assume that ‘forgiveness to non-completion’ (one of the regimen properties listed in Table 2) applies only to the latter, with the parameter f being the proportion interrupting treatment who nonetheless have the same outcomes as those completing treatment. R denotes individuals who have reverted to their pre-regimen state of TB infection, following decay of any post-regimen protection. d denotes the per-capita hazard of regimen interruption and thus governs ease-of-adherence, b directly models the drug-resistance barrier and m governs the regimen duration. These and remaining model parameters are as listed in Additional file 2: Table S2

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