3.1 Epidemic caused by one case of imported AII
3.1.1 Probability of community outbreak and incidence among residents
Outbreak was defined as the occurrence of more than 10 patients or more than 20 AIIs within the community. There were 3,300 households within the community, and approximately 10,300 residents. Figure 1a1 shows that when R0 = 1.2, p = 0.2, and q = 0, and under the conditions of an outbreak, the median infection rate of AIIs and median incidence rate of patients at 730 d of the epidemic were 0.22 and 0.06, respectively. As q increased, the infection rate and incidence rate decreased. When q = 1, their medians decreased to 0.01 and 0.005, respectively. Figure 1a2 shows that compared with R0 = 1, when R0 = 1.2, the probability of patients and AIIs to cause an outbreak increases.
3.1.2 Temporal distribution of the cumulative number of new AIIs and patients in the absence of interventions
Figure 1b shows that without the tracing of infection sources and close contacts and without the home quarantine of AIIs, given the premise of a community outbreak, the cumulative number of AIIs and patients during a community outbreak increased from almost 0 to 3,653 (25%–75% percentile [50% P]: 3,529–3,741) and 907 (50% P: 875–949), respectively.
3.1.3 Epidemic trends in the presence of interventions
Figure 1c shows that if the tracing of infection sources and close contacts and the home quarantine of AIIs after detection were implemented, given the premise of a community outbreak, the number of AIIs and patients increased to 1,381 (50% P: 1,092–1,620) and 340 (50% P: 272–414), respectively, when t = 730. In the absence of interventions, the medians of the two groups decreased by 62.2% and 62.5%, respectively. Figure 1d shows that the number of undetected AIIs and patients initially increased, but eventually decreased to 0. The proportion of AIIs and COVID–19 patients peaked at 302 d, reaching 53 (50% P: 27–71) and 20 individuals (50% P: 10–25), respectively. Moreover, Figure 1e shows that the number of quarantined individuals and households initially increased, but eventually decreased to 0. The peaks of the two groups appeared at 333 d, reaching 49 individuals (50% P: 26–65) and 14 households (50% P: 6–21), respectively.
3.2 Epidemic caused by 1,000 AIIs in the presence of interventions
3.2.1 Temporal distribution of the number of new AIIs and patients
Figure 2a shows that given the conditions of p = 0.2 and q = 0.5, when R0 were 0.8, 1.2, and 1.6, the number of newly infected persons peaked at 13 d, 14 d, and 17 d, respectively, reaching 70 (50% P: 66–76), 81 (50% P: 74–87) and 91 individuals (50% P: 86–97). Figure 2b shows that the number of patients peaked at 13 d, 15 d, and 16 d, respectively, reaching 10 (50% P: 7–13), 16 (50% P: 13–19) and 21 individuals (50% P: 17–24), respectively.
3.2.2 Temporal distribution of the cumulative number of new AIIs and patients
Figure 2c shows that when R0 were 0.8, 1.2, and 1.6, the cumulative number of newly infected persons at 180 d of the epidemic reached 2,573 (50% P: 2,491–2,624), 3,854 (50% P: 3,766–3,933), and 4,971 individuals (50% P: 4,918–5,027), respectively. Figure 2d shows that the cumulative number of new patients at 180 d of the epidemic reached 392 (50% P: 373–408), 692 (50% P: 661–724), and 962 individuals (50% P: 933–986), respectively.
3.2.3 Temporal distribution of the number of undetected AIIs and patients
Figure 2e shows that when R0 were 0.8, 1.2, and 1.6, the number of undetected AIIs in the infection period peaked within 3 d, 7 d, and 10 d of the epidemic, reaching 1,013 (50% P: 1,001–1,029), 1,173 (50% P: 1,150–1,188), and 1,391 individuals (50% P: 1,370–1,416), respectively. Figure 2f shows that the number of undetected patients in the infection period peaked at 10 d, 11 d, and 13 d of the epidemic, reaching 43 (50% P: 38–47), 66 (50% P: 60–71), and 92 individuals (50% P: 86–97), respectively.
3.2.4 Temporal distribution of the number of quarantined households and residents
Figure 2g shows that when R0 were 0.8, 1.2, and 1.6, the number of quarantined households peaked at 20 d, 21 d, and 24 d of the epidemic, reaching 169 (50% P: 160–184), 258 (50% P: 244–269), and 345 households (50% P: 325–362), respectively. Figure 2h shows that the number of quarantined residents peaked at 20 d, 21 d, and 22 d of the epidemic, reaching 571 (50% P: 525–628), 888 (50% P: 838–924), and 1,208 individuals (50% P: 1,130–1,272), respectively.
3.3 Sensitivity analyses
In this study, sensitivity analyses of the five parameters and a continuous time series of the sum of asymptomatic infected individuals and patients each day were conducted. We took 500 samples from a uniform distribution for each parameter range. PRCCs near –1 or +1 indicate that the parameter has a strong negative or positive impact on the output, respectively, whereas those closer to 0 indicate less effect on the output result for that parameter (Figure 3). The results reflected that R0, R1, and p had positive effect on the model outputs; meanwhile, \* MERGEFORMAT and q had a negative effect on the model outputs.