How many COVID-19 PCR positive individuals do weexpect to see on the Diamond Princess cruise ship?

Qin, J.; Chen, F.; Ma, H.; Liu, Y.; Follmann, D.; Zhou, Y.

When COVID-19 was detected among passengers on Diamond Princess (DP) cruise ship in the end of January and beginning of February of this year, unfortunately it has become an ideal experimental model for studying the transmission potential of COVID-19 in a closed environment while it is hard to do so in the wider open population. Information collected from such an outbreak is crucial for policy makers to understand and manage the epidemic. To disclose the information such as infection onset time, transmission time, and so on from the available observed incomplete data, we must develop valid statistic models and solid inference methods. Due to the fact that the priority for RT-PCR test for COVID-19 was given to symptomatic and their close contacts and elderly individuals, we have to take this selection bias into considerations in the statistic inference. Based on RT-PCR test data performed on the Diamond Princess cruise, in this paper we propose a novel mixture model where the mixing proportions vary with time to estimate the infection distribution and the total infected individuals after a 14-day of quarantine. Compared with the epidemiologic description of COVID-19 spread in open space, we have found some unique features in the Diamond Princess cruise ship. Our fndings may shed lights on preventing future pandemic outbreaks in cruise ship.