The impact of changes in the necessary tracing period and the actual coverage for the STAP intervention were investigated (Fig. 5). The mean numbers of total patients and persons treated with antiviral drugs for prophylaxis with 95% CIs for 90 days after the introduction of the initial patient and also the numbers of cases prevented per person treated with antiviral drugs for prophylaxis are shown in Table 4. For situations with a necessary tracing period of 2 days with 30% coverage, the mean number of total patients for 90 days would be decreased to 1.4% compared with the baseline. However, there were no significant differences in the number of patients for a necessary tracing period of 2, 4, and 6 days, respectively or for a coverage of 30, 50, and 70%, respectively. The ripple effect of the administration of antiviral drugs in STAP on the reduction of patient numbers was estimated to be 10.2- and 6.1-fold for a necessary tracing period of 6 days with 30% coverage and 2 days with 70%, respectively, which indicates that STAP intervention would have a weaker ripple effect than TAP.
Fig. 5 Comparison of the total number of patients (a) and the number treated with antiviral drugs (b) for 90 days with a tracing coverage of 30, 50, and 70%, respectively, and a necessary tracing period of 2, 4, and 6 days, respectively, for the STAP intervention. The squares show the mean value for 100-trial simulations with error bars showing the 95% CI. Grey, light grey, and white squares show the situations for necessary tracing periods of 2, 4, and 6 days, respectively