Just 2% of SARS-CoV-2−positive individuals carry 90% of the virus circulating in communities

Abstract

We analyze data from the fall 2020 pandemic response efforts at the University of Colorado Boulder, where more than 72,500 saliva samples were tested for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using qRT-PCR. All samples were collected from individuals who reported no symptoms associated with COVID-19 on the day of collection. From these, 1,405 positive cases were identified. The distribution of viral loads within these asymptomatic individuals was indistinguishable from what has been previously observed in symptomatic individuals. Regardless of symptomatic status, ∼50% of individuals who test positive for SARS-CoV-2 seem to be in noninfectious phases of the disease, based on having low viral loads in a range from which live virus has rarely been isolated. We find that, at any given time, just 2% of individuals carry 90% of the virions circulating within communities, serving as viral “supercarriers” and possibly also superspreaders.

SARS-CoV-2 and the role of airborne transmission: a systematic review

“…The authors also appear to expect that live virus should be detectable in all locations where COVID-19 patients are present. However, it is clear that viral load is extremely variable both in time (He et al 2020) and between people (Yang et al 2021). Aerosol generation is also highly variable among different people (Asadi et al 2019;Edwards et al 2021).…”

Testing Saliva to Reveal the Submerged Cases of the COVID-19 Iceberg

“…While an estimated 7.5% of SARS-CoV cases and 9.8% of MERS-CoV (Wilder-Smith et al, 2005 ; Al-Tawfiq, 2020 ) cases remained asymptomatic, current estimates suggest that anywhere from 17 to 30% of SARS-CoV-2 positive subjects remain asymptomatic (Pollock and Lancaster, 2020 ; Johansson et al, 2021 ). As SARS-CoV-2 viral load in paucisymptomatic and asymptomatic subjects has been shown to not differ from those with symptoms (Yang et al, 2021 ), asymptomatic individuals can silently spread SARS-CoV-2 throughout their communities.…”

Epidemic dynamics in inhomogeneous populations and the role of superspreaders

“…This assumption may be justified when differences in the salient parameters are small. However, one of the interesting features of the current COVID-19 pandemic is the huge variation in infectivity: small numbers of infectious events or individuals seem to be responsible for a large number of cases [2–14]. This feature seems to be present in other coronavirus epidemics including SARS [15–17] and MERS [18–20].…”

“…This feature seems to be present in other coronavirus epidemics including SARS [15–17] and MERS [18–20]. One can point to different explanations for this phenomenon: individual variations in viral load and shedding [14, 21, 22], in droplet production (see the review in [23]), in contact networks [8, 10, 12, 24, 25], and differences in the features of ventilation systems at certain events and venues [26, 27]. Inhomogeneity seems to have played an important role for other epidemics as well [28–30], leading to the rule of thumb that “20% of patients produce 80% of infections” [31].…”