Estimation of monkeypox spread in a non-endemic country considering contact tracing and self-reporting: a stochastic modeling study

Background In May 2022, monkeypox started to spread in non-endemic countries. After the number of confirmed cases reached more than 16,000 in July, the World Health Organization declared the highest alert over the outbreak. Methods To investigate the effects of contact tracing and self-reporting of primary cases in the local community, a stochastic model is developed. A delay simulation algorithm based on Gillespie’s stochastic chemical kinetics is used to quantify the number of infections, contacts made by the infectors, and duration from the arrival of the primary case until the detection of the index case (and until there are no more local infections), under various scenarios. Results We found that if the primary case does not self-report, taking into account a population of 10,000, the average number of infections could range from 30 to 67, while the number of contacts made by infectors could range from 221 to 498. On the other hand, if the primary case self-reports, the average number of infections and contacts could range from 5 to 7 and 40 to 52, respectively. The average duration from the primary case arrival until the first index case detection (or until there are no more local infections) ranged from 8 to 10 days (18 to 21 days) if the primary case does not self-report, and approximately 3 days (8 days) if the primary case self-reports. Moreover, if the number of close contacts per day is doubled in our simulation settings, then the number of infections could increase by 53%. Conclusion The number and duration of the infections are strongly affected by the self-reporting behavior of the primary case and the delay in the detection of the index case. Our study emphasizes the importance of border control, which aims to immediately detect the primary case before secondary infections occur.