COVID-19 project believes infections estimates should include all infected individuals of the SARS-CoV-2 virus, not just those that took a COVID-19 test and tested positive. As of January 2021, they estimate the true number of infected individuals in the US to be roughly 2-4x higher than the reported cases (20-50% detection rate). See our writeup, Estimating True Infections, for a more detailed look into this subject. Because not all currently infected individuals are infectious, they recommend dividing the “currently infected” estimate by 2-4 to get a sense of the number of currently infectious individuals.
Source: COVID-19 Projections