Why Is COVID-19 So Infectious?

Respiratory diseases, such as COVID-19 can be spread via droplet transmission in aerosols. Recent studies have shown that exhalations, sneezes, and coughs create a gas cloud that can extend the lifetime of a droplet and increase the trajectory of this cloud further than was originally thought. In fact, gas clouds from actions such as sneezing have been proven to span as far as 23 feet to 27 feet.¹

With the rising number of positive COVID-19 cases across the nation, it is important to understand why the virus is so infectious so that we may better protect ourselves. The pathogenesis of the virus shows that the lung epithelial cells are the primary target for COVID-19 and, thus, actions like sneezing can spread the virus through aerosols.² Current studies are indicating a high level of virus titers in the oropharynx area when symptoms are not yet present.³ A study on those initially infected in Wuhan, China showed an average incubation period of 5.2 days, with 95% of cases showing symptoms by day 12.5.⁴ During this time, it was estimated that each infected person had spread the virus to an average of 2.2 more people. Experts state that until this number drops below 1, we will continue to see a spike in the number of new cases.⁴

The other factor that plays into the novel coronavirus’ contagiousness is its ability to survive outside of the body. One study showed that the virus, although reduced, was still viable for 3 hours within aerosols and up to 72 hours on surfaces such as plastics and stainless steel. Cardboard and copper were also tested, and while the virus was found to be less stable, it was still detected up to 4 hours later on copper surfaces and up to 24 hours later on cardboard.⁵

This creates an interesting dilemma for the dental professional who has direct patient contact. Procedures that create aerosols can lead to exposure of these microorganisms, including viruses. Many areas have restricted patient contact to emergency procedures only, but it is important to stay vigilant when following infection control guidelines. The use of N95 masks has been recommended for those dealing with direct patient contact for their ability to filter out 95% of incoming aerosolized droplets.⁶

With COVID-19 possibly more than three times as infectious as the flu, according to Robert R. Redfield, MD, director of the US Centers for Disease Control and Prevention (CDC), new recommendations are being released on a daily basis so keep checking for any new information released by the CDC.

References

1. Bourouiba, L. Turbulent gas clouds and respiratory pathogen emissions Potential implications for reducing transmission of COVID-19. JAMA. 2020. Available at: https://jamanetwork.com/journals/jama/fullarticle/2763852?resultClick=1
2. Rothan HA, Byrareddy SN. The epidemiology and pathogenesis of coronavirus disease (COVID-19) outbreak. J Aut. 2020. Available at: https://www.sciencedirect.com/science/article/pii/S0896841120300469?via%3Dihub
3. Fauci AS, Lane HC, Redfield RR. COVID-19—Navigating the uncharted. N Engl J Med. 2020; 382:1268-1269. Available at: https://www.nejm.org/doi/full/10.1056/NEJMe2002387
4. Li Q, Guan X, Wu P, et al. Early transmission dynamics in Wuhan, China, of novel coronavirus-infected Pneumonia. N Engl J Med. 2020; 382: 1199-1207. Available at https://www.nejm.org/doi/full/10.1056/NEJMoa2001316
5. van Doremalen N, Bushmaker T, Morris DH, et al. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med. 2020. Available at https://www.nejm.org/doi/full/10.1056/NEJMc2004973
6. US Centers for Disease Control and Prevention. Coronavirus Disease 2019 (COVID-19)-FAQ About Personal Protective Equipment. Available at https://www.cdc.gov/coronavirus/2019-ncov/hcp/respirator-use-faq.html