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 (USA), where more than 72,500 saliva samples were tested for SARS-CoV-2 using quantitative RT-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 reported in symptomatic individuals. Regardless of symptomatic status, approximately 50% of individuals who test positive for SARS-CoV-2 seem to be in non-infectious 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 super-carriers and possibly also super-spreaders.

Higher viral load drives infrequent SARS-CoV-2 transmission between asymptomatic residence hall roommates

“…We found transmission rates similar to studies involving mostly symptomatic populations, supporting the idea that asymptomatic infected individuals can transmit as efficiently as symptomatic individuals (Madewell et al, 2020). This is strengthened by the observation that viral loads are similar between symptomatic and asymptomatic individuals (Lennon et al, 2020;Yang et al, 2021).…”

“…Residential students were required to test weekly with each residence hall assigned to a day of the week, thus treating each hall as a cohort. The screening test was developed at CU Boulder and is described in detail elsewhere, including primer and probe sequences and fluorophores along with example standard curves (Yang et al, 2021). Briefly, students selfcollected 1 mL saliva under observation at designated on-campus sites.…”

“…The factors underlying this variable transmission risk are a matter of intense scrutiny. Although many studies have found a broad range in viral load over 6 orders of magnitude or more (Kissler et al, 2020;Lennon et al, 2020;Yang et al, 2021), whether this contributes to the risk of transmission is unclear. In addition, time spent with a close contact is also a potential contributing factor, but understanding its impact is hampered by differences in isolation practices and variability in the timing of case detection.…”

“…However, studies with high testing penetrance of large populations indicate that 40-90% of cases may be asymptomatic (Lavezzo et al, 2020;Lennon et al, 2020;Poletti et al, 2020). Importantly, asymptomatic infected individuals still transmit virus and show no difference in peak viral load compared to symptomatic individuals, and they are also expected to be more mobile because they are not experiencing illness (Cevik et al, 2021;Lavezzo et al, 2020;Lee et al, 2020;Yang et al, 2021). Therefore, it is critical to study this potentially large reservoir of viral carriers.…”

A novel RT-LAMP workflow for rapid salivary diagnostics of COVID-19 and effects of age, gender and time from symptom onset

“…Based on these observations, we suggest that salivary diagnostics in symptomatic individuals should be performed as soon as possible after symptom onset to increase chances of detection, especially for young females. Recent reports show that saliva has higher sensitivity than nasal/nasopharyngeal swabs to identify asymptomatic cases (41), and that viral load distribution is equivalent in saliva from symptomatic and nonsymptomatic individuals (42). Therefore, rapid salivary diagnostics stands as an invaluable opportunity to efficiently monitor and curb SARS-CoV-2 transmission.…”