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Table 1 Detailed model scenarios and operationalization

From: The positive externalities of migrant-based TB control strategy in a Chinese urban population with internal migration: a transmission-dynamic modeling study

Scenarios Approach Model operationalization and parameters
Scenario 1. Improved TB case-finding in the elderly of residents (65+ years old) Residents aged 65 years old and above currently receive a routine annual health check, which includes TB screening but with low sensitivity. This intervention would increase the sensitivity of this screen. • Assumed to produce a rate of transition from early and late active disease states to treatment state.
• Only applies to population 65 years and above among residents.
• Transition rate calculated as rate of screening appointments * incremental improvement in sensitivity.
• Rate of screening appointments = 1.0
• Incremental improvement in sensitivity = 10%
Scenario 2. Treatment of latent infection in the elderly (65+ years old) At the annual health check-up for the elderly, residents screening TB negative would receive a TST, and those testing positive would receive prevent treatment (6H). Individuals would be screened once every 5 years. • Only applies to population 65 years and above among residents.
• For simplicity, assumed to exclude those with active TB and those on TB treatment.
• Transition rate calculated as rate of screening appointments * TST sensitivity * treatment uptake probability * treatment completion probability.
• Rate of screening appointments = 1.0
• TST sensitivity = 88% (95%CI 80–95) [33]
• Treatment uptake probability = 35%(20–50%) [34,35,36,37]
• Treatment completion probability = 70% (60–80%) [38]
• Relative risk (RR) of developing active TB under prevent treatment (> 2 years) = 0.40 (0.30–0.50) [39]
Scenario 3. Pre-employment TB screening in migrants A one-time active TB screening for migrants at time of first employment in the district. • Assumed to produce a rate of transition from early and late active disease states to treatment state.
• Only applies to migrants entering the model.
• Applied as a probability of transition at the time of model entry. Probability calculated as screening sensitivity * diagnosis sensitivity * treatment initiation probability
• Screening sensitivity = 90% (80–95%) for the late active disease (45%, for early status) [40]
• Diagnosis sensitivity = 90% (80–95%) (smear test, liquid culture, and Xpert MTB/RIF)
• Treatment initiation probability = 100%
Scenario 4. Pre-employment TB and LTBI screening in migrants As in Scenario 3, plus LTBI screening and treatment for those screening negative for active TB • Assumed to produce a rate of transition from latent fast and latent slow states to the partially immune state.
• Applies to the same group as the scenario above.
• For simplicity, assumed to exclude those with active TB and those on TB treatment.
• Applied as a probability of transition at the time of model entry. Probability calculated as TST sensitivity * treatment uptake probability * treatment completion probability
• TST sensitivity = 88% (80–95%) [33]
• Treatment uptake probability = 35% (20–50%) [34,35,36,37]
• Treatment completion probability = 70% (60–80%) [38]
• Relative risk (RR) of developing active TB under prevent treatment (> 2 years) = 0.40, (0.30 to 0.50) [39]
Scenario 5. Routine active TB screening in factories Regular active TB screening for individuals working in manufactories. Assumed screen algorithm: screening either for cough lasting for longer than 2 weeks, or screening for any symptom compatible with TB; Then chest radiography test. • Assumed to produce a rate of transition from early and late active disease states to treatment state.
• Applies to migrants work at the manufactory (62% of total migrant population, Fig. S3)
• Transition rate calculated as rate of screening appointments * screening sensitivity * diagnosis sensitivity * treatment initiation probability
• Rate of screening appointments = 1.0
• Screening sensitivity = 90% (80–95%) for the late active disease (45%, for early status) [40]
• Diagnosis sensitivity = 90% (80–95%) (smear test, liquid culture, and Xpert MTB/RIF)
• Treatment initiation probability = 100%