  Due to the complexities of virus genotypes and the stochastic contacts in
human society, it is a big challenge to estimate the potential risks of getting
exposed to a widely spreading virus. To allow the public to be aware of the
exposure risks in their daily activities, we proposed a birthday-paradox-based
probability model and implement it into a web-based system named COSRE for
estimating community exposure risks of public gathering during a pandemic. The
exposure risk means the probability of people meeting potential COVID hosts in
public places like grocery stores, gyms, libraries, restaurants, coffee shops,
office suits, etc. The model has three inputs: the real-time potential active
patients, the population in local communities, and the customer counts in the
room. With COSRE, people can explore the possible impacts of the pandemic by
doing spatiotemporal analysis, e.g., moving through time and testing a
different number of people to see the changes of risks as the pandemic unfolds.
The system has the potential to advance our ability to know the accurate
exposure risks in various communities and allow us to make plans with improved
preparedness and precise responses for the pandemic. We use spatial analysis
tools and drew the county-level exposure risks of the United States from April
1 to May 15. The experiment shows that the estimation model is very promising
to assist people to be more specifically precise about their safety control in
daily routine and social lives and help businesses to dynamically adjust their
COVID-19 policies to accelerate their recovery.
