How does coronavirus disease 2019 (COVID-19) spread?

Updated: Jun 25, 2021
  • Author: David J Cennimo, MD, FAAP, FACP, FIDSA, AAHIVS; Chief Editor: Michael Stuart Bronze, MD  more...
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Answer

The principal mode by which people are infected with SARS-CoV-2 is through exposure to respiratory droplets carrying infectious virus (generally within a space of 6 feet). Additional methods include contact transmission (eg, shaking hands) and airborne transmission of droplets that linger in the air over long distances (usually greater than 6 feet). [31, 32, 33]  Virus released in respiratory secretions (eg, during coughing, sneezing, talking) can infect other individuals via contact with mucous membranes.

On July 9, 2020, the World Health Organization issued an update stating that airborne transmission may play a role in the spread of COVID-19, particularly involving “super spreader” events in confined spaces such as bars, although they stressed a lack of such evidence in medical settings. Thus, they emphasized the importance of social distancing and masks in prevention. [33]

The virus can also persist on surfaces to varying durations and degrees of infectivity, although this is not believed to be the main route of transmission. [31]  One study found that SARS-CoV-2 remained detectable for up to 72 hours on some surfaces despite decreasing infectivity over time. Notably, the study reported that no viable SARS-CoV-2 was measured after 4 hours on copper or after 24 hours on cardboard. [34]

In a separate study, Chin and colleagues found that the virus was very susceptible to high heat (70°C). At room temperature and moderate (65%) humidity, no infectious virus could be recovered from printing and tissue papers after a 3-hour incubation period or from wood and cloth by day two. On treated smooth surfaces, infectious virus became undetectable from glass by day 4 and from stainless steel and plastic by day 7. “Strikingly, a detectable level of infectious virus could still be present on the outer layer of a surgical mask on day 7 (~0.1% of the original inoculum).” [35]  Contact with fomites is thought to be less significant than person-to-person spread as a means of transmission. [31]

Utilizing a decision analytical model, Johansson et al from the US Centers for Disease Control and Prevention assess transmission from presymptomatic, never symptomatic, and symptomatic individuals across various scenarios to determine the infectious period of transmitting SARS-CoV-2. They estimate at least 50% of new SARS CoV-2 infections originated from exposure to individuals with infection, but without symptoms. [44]

 


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