Figure 2.

Contact investigation program as implemented in the model; A) case management procedure. “Infectious” refers to pulmonary active TB; depending on the contact investigation program considered, a negative smear status does not necessarily imply a conclusion of the case management procedure: for this reason the arrow corresponding to the N option in the block labeled “Smear+?” is represented with a dotted line. B) Contact tracing procedure. For a fraction of contacts in the list, the procedure ends with no further action, representing contacts which could not be reached. If the contact is actually traced, action is taken according to its epidemiological status. For uninfected individuals, the algorithm will end with no further action. In a case of active disease, individuals may be correctly diagnosed and cured (in this case, cure is assumed instantaneous) and a new case management procedure for elicitation of its contacts is started. If the contact was recently or remotely (LTBI) infected, a protein-purified derivative (PPD) test is simulated. If the test is positive the contact can initiate and complete LTBI treatment with given probabilities. The contact is assumed to heal completely and moves to the susceptible compartment only if LTBI treatment is completed. If the PPD result is negative, a repetition of the test is performed in 8–10 weeks, during which time the individual’s epidemiological status may change. If a second PPD test is negative, the procedure ends with no further action. All details are provided in the Technical Appendix.