  The COVID-19 pandemic has plagued the world for months. The U.S. has taken
measures to counter it. On a daily basis, newly confirmed cases have been
reported. In the early days, these numbers showed an increasing trend.
Recently, the numbers have been generally flattened out. This report tries to
estimate the hidden number of currently alive infections in the population by
using the confirmed cases. A major result indicates an existing infections
estimate at about 10-50 times the daily confirmed new cases, with the stringent
social distancing policy tipping to the upper end of this range. It clarifies
the relationship between the infection rate and the test rate to put the
epidemic under control, which says that the test rate shall keep up at the same
pace as infection rate to prevent an outbreak. This relationship is meaningful
in the wake of business re-opening in the U.S. and the world. The report also
reveals the connections of all the measures taken to the epidemic spread. A
stratified sampling method is proposed to add to the current tool kits of
epidemic control. Again, this report is a summary of some straight observations
and thoughts, not through a thorough study backed with field data. The results
appear obvious and suitable for general education to interested policymakers
and the public.
