“The new corona virus disease 2019 (COVID-2019) is rapidly spreading through the world. With insufficient testing, available case data may underestimate the total number of infections. We statistically estimated the cumulative number of cases with confidence intervals from the reported number of deaths, assuming that the number of infections grow exponentially with a constant doubling time. Our findings indicate that the number of unreported infections is likely at least one order of magnitude higher than the reported cases, in particular in the United States and the United Kingdom. This finding is supported by a recent mass screening for SARS-CoV-2 in Iceland which found that the actual case numbers may be about 20 times higher than the officially reported number.”
Current number of reported cases in the U.S. is 277,161. An order of magnitude higher would be 2.8 million cases. Then 20 times higher would be 5,540,000 cases. So this study puts the real number of cases in the U.S. in the range of 2.8 to 5.5 million, rather than a quarter million.
Here is a link to the full study.