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

By March 12, there were a total of 1,514 reported cases and 39 reported deaths that resulted from local transmission of SARS-CoV-2 in the US. We used this information to estimate the probability of detecting imported symptomatic infections, ρ travel , by seeding our model with imported infections, simulating local transmission, and comparing simulated and reported local deaths. Under our baseline scenario, this resulted in a median estimate of ρ travel = 0.39 (95% posterior predictive interval: 0.15 -0.90). Simulating from January 1, we obtained 22,876 (95% PPI: 7,451 -53,044) local infections cumulatively in the US by March 12 (Fig. 1A) . Due to the exponential growth posited by our model, 2,958 (95% PPI: 956 -7,249) local infections were predicted to have occurred on March 12 alone (Fig. 1B) . Had we performed a simple extrapolation of reported cases and deaths based on ρ travel , our estimate of cumulative local infections by March 12 would have been only 5,018 (95% PPI: 2,350 -12,445). This suggests that detection of local infections was less sensitive than detection of imported infections.