Using influenza surveillance networks to estimate state-specific prevalence of SARS-CoV-2 in the United States

Abstract

Detection of SARS-CoV-2 infections to date has relied heavily on RT-PCR testing. However, limited test availability, high false-negative rates, and the existence of asymptomatic or sub-clinical infections have resulted in an under-counting of the true prevalence of SARS-CoV-2. Here, we show how influenza-like illness (ILI) outpatient surveillance data can be used to estimate the prevalence of SARS-CoV-2. We found a surge of non-influenza ILI above the seasonal average in March 2020 and showed that this surge correlated with COVID-19 case counts across states. If 1/3 of patients infected with SARS-CoV-2 in the US sought care, this ILI surge would have corresponded to more than 8.7 million new SARS-CoV-2 infections across the US during the three-week period from March 8 to March 28, 2020. Combining excess ILI counts with the date of onset of community transmission in the US, we also show that the early epidemic in the US was unlikely to have been doubling slower than every 4 days. Together these results suggest a conceptual model for the COVID-19 epidemic in the US characterized by rapid spread across the US with over 80% infected patients remaining undetected. We emphasize the importance of testing these findings with seroprevalence data and discuss the broader potential to use syndromic surveillance for early detection and understanding of emerging infectious diseases.

COVID ‐19 pandemic‐related lockdown: response time is more important than its strictness

“…Therefore, under these two assumptions, initiating a lockdown as early as a period equal to the doubling time would result in half as many death incidents. Other studies estimated the doubling time to be lower than 4 days (Lurie et al , 2020; Muniz‐Rodriguez et al , 2020; Silverman et al , 2020). Notably, all of the aforementioned studies were conducted on infection or mortality data collected during different time phases between December 2019 and the beginning of March 2020, and it is possible that the effective doubling time diverged across countries and through time.…”

Tracking the onset date of the community spread of SARS-CoV-2 in western countries

“…(11,22,23,24) Our findings also agree with epidemiological data from syndromic surveillance of severe acute respiratory illness (SARI) that detected an excess of non-influenza SARI cases above the seasonal average in France, the USA and Brazil since late-February/early-March and further confirm SARS-CoV-2 positive samples among hospitalised SARI cases in Brazil since mid-February (16th-22nd February) (Available from: http://info.gripe.fiocruz.br). (9,41,42) The TN1 projections and the molecular clock analyses provide quite convergent estimates of the probable onset date of community transmission of SARS-CoV-2 in those locations where the epidemic was mostly driven by one seeding event. For countries with evidence of few and multiple independent seeding events, however, our TN10 and TN100 projections push back the timeline of community spread 10-20 days earlier than molecular clock estimates, respectively.…”

“…The high proportion of asymptomatic/presymptomatic infectious individuals coupled with limited testing might have facilitated the undocumented dissemination of the novel coronavirus between and within countries before its detection by public health systems. (8,9) Consistent with this hypothesis, one study retrospectively identified the presence of SARS-CoV-2 in a patient with no history of recent travel that was hospitalised in France in late December 2019. (10) This early detection of the virus in Europe in December 2019, however, did not demonstrates that community transmission chains detected several weeks later actually originated from this very first case.…”

Validating and modeling the impact of high-frequency rapid antigen screening on COVID-19 spread and outcomes

“…As of 25 September 2020, there have been more than 32.1 million confirmed cases globally with more than 980,000 confirmed deaths (1). However, these numbers and the current mapping of disease spread present an incomplete picture of the outbreak largely due to the lack of adequate testing, particularly as undetected infected cases are the main source of disease spread (2)(3)(4)(5)(6)(7). It is estimated that the reported detection rate of actual COVID-19 cases is only 1-2% (5).…”