Estimating unobserved SARS-CoV-2 infections in the United States

Alex Perkins; Sean M. Cavany; Sean M Moore; Rachel J Oidtman; Anita Lerch; Marya Poterek

We estimated the probability of detecting local symptomatic infections, ρ local , by comparing our model's predictions of symptomatic infections to local case reports on a daily basis. Over the course of February, daily estimates of ρ local decreased from our uniform prior down to a low of 0.033 (95% PPI: 0.012 -0.12) on February 21, as increases in simulated local infections outpaced newly reported local cases ( Fig. 2A) . Our results indicate that detection of symptomatic infections was below 20% for nearly a month (median: 29 days, 95% PPI: 17 -37 days) when containment still might have been feasible. As testing increased in March (Fig. 2B , red), so too did reported cases ( Fig. 2A , red) and daily estimates of ρ local (Fig. 2B , black). By March 12, we estimated ρ local to be 0.77 (95% PPI: 0.29 -1.00). Between February 21 (low estimate of ρ local ) and March 12, our daily estimates of ρ local were well correlated with daily numbers of tests administered (Pearson's correlation, median: 0.97, 95% PPI: 0.85 -0.98).