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

Abstract

By March 2020, COVID-19 led to thousands of deaths and disrupted economic activity worldwide. As a result of narrow case definitions and limited capacity for testing, the number of unobserved severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections during its initial invasion of the United States remains unknown. We developed an approach for estimating the number of unobserved infections based on data that are commonly available shortly after the emergence of a new infectious disease. The logic of our approach is, in essence, that there are bounds on the amount of exponential growth of new infections that can occur during the first few weeks after imported cases start appearing. Applying that logic to data on imported cases and local deaths in the United States through 12 March, we estimated that 108,689 (95% posterior predictive interval [95% PPI]: 1,023 to 14,182,310) infections occurred in the United States by this date. By comparing the model’s predictions of symptomatic infections with local cases reported over time, we obtained daily estimates of the proportion of symptomatic infections detected by surveillance. This revealed that detection of symptomatic infections decreased throughout February as exponential growth of infections outpaced increases in testing. Between 24 February and 12 March, we estimated an increase in detection of symptomatic infections, which was strongly correlated (median: 0.98; 95% PPI: 0.66 to 0.98) with increases in testing. These results suggest that testing was a major limiting factor in assessing the extent of SARS-CoV-2 transmission during its initial invasion of the United States.

On Pilot Massive COVID-19 Testing by Antigen Tests in Europe. Case Study: Slovakia

“…According to these scenarios, the RT–PCR testing policy in Slovakia was able to trace approximately 11% of all infected individuals in the population for the given period. A similar situation was in China, Italy or in the USA, where scientists projected that the number of confirmed cases in hotspots could oscillate between 10 and 20% of all infected people [ 21 , 22 , 23 ].…”

Differential effects of intervention timing on COVID-19 spread in the United States

“…The Pearson correlation coefficient is 0.76, indicating a general agreement in trend. A recent study estimated that 108,689 (95% CI: 1023 to 14,182,310) infections occurred in the United States before 12 March 2020 ( 41 ). Our inference estimated 236,207 (95% CI: 193,855 to 298,937) total infections in the United States by that date, which is within the CI and in line with the magnitude of the best estimate from that study.…”

Optimal Allocation of Limited Test Resources for the Quantification of COVID-19 Infections

“…The proposed methodology is, to the best of our knowledge, the first method to propose an optimal spatio-temporal allocation of limited test-kit resources. A first study for the estimate of unobserved COVID-19 infections [5] in the USA indicated that early testing would have decreased the surveillance gap during a critical phase of the epidemic. More recently a number of studies have emerged that address the optimal allocation of resources.…”

“…While there is valuable information being gathered, their estimates rely on testing individuals that are either already symptomatic or have been selected based on certain criteria (hospital visits, airport arrivals, geographic vicinity to researchers, etc.). Generic, randomized tests of the population are broadly applied but they have been hampered either by delays [5] or by insufficient numbers of test kits [6]. There is broad recognition that efficient testing strategies are critical for the timely identification of infectious individuals and the optimal allocation of resources [7].…”