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Transmission and Prevention of COVID-19
Eve Cuny, MS
The world has experienced nearly a full year of the longest and most serious pandemic in 100 years. During this year, medical scientists have amassed an astounding amount of evidence regarding the transmission and prevention of COVID-19. Although more information is certain to emerge as the scientific community continues to explore this novel disease, there are things that can be done now to make dental care as safe as possible for dental healthcare personnel (DHCP) and their patients.
Transmission Routes for COVID-19
To understand how to prevent the spread of diseases, one must first explore and understand the transmission routes. One classification for modes of transmission for infectious diseases describes direct and indirect transmission. Direct transmission includes direct contact and droplet spread. Indirect transmission includes airborne, vehicle borne, and vector borne1 (Table 1). Respiratory viruses may be transmitted through contact, droplets, or via the airborne route.2 Droplet transmission occurs when a person is exposed to droplets of varying sizes and particles when near an infected person. These droplets tend to fall to the ground and surfaces relatively quickly, which is why the recommendation for maintaining a 6-foot distance from others relates to droplet-transmissible diseases.2 Airborne transmission results when exposed to smaller droplets and particles capable of traveling greater distances over longer periods of time.
Early in the pandemic, health experts warned that COVID-19 most likely spread through contact with respiratory droplets that are released when an infected person coughs, sneezes, or speaks. One study did explore the survival of the SARS-CoV-2 virus on a variety of surfaces, but it is now believed that contact with contaminated surfaces or objects is not a common means by which the virus is transmitted.3,4 What had been uncertain from the beginning of the pandemic was the extent to which COVID-19 may be transmitted as an airborne infection.5 Increasingly, evidence is showing that COVID-19 can be transmitted via the airborne route, over greater time and distance that was first believed.6-8
On October 5, 2020, the Centers for Disease Control and Prevention (CDC) issued an updated description of how COVID-19 spreads.4 The agency describes a virus that spreads easily from person to person via respiratory droplets that are released when an infected person coughs, sneezes, sings, talks, or breathes-the droplet route. The report also concludes that although it is not the most common way COVID-19 is spread, that airborne transmission is possible under certain circumstances. These include an enclosed space where an infectious individual is generating respiratory droplets for a prolonged period (>30 minutes to hours). People in the space greater than 6 feet away from the infected person, or people who have passed through shortly after the infected person left, may have been infected in this way.2 Inadequate ventilation or air handling that allowed a build-up of suspended respiratory droplets and particles has also been implicated in airborne transmission.
The recommended precautions for infection prevention related to COVID-19 should be viewed as a tiered approach, with varying strategies for the different levels of potential exposure. For the general population, the focus continues to be source control. In a July 2020 report, the CDC indicated that, according to their best estimate, approximately 40% of all COVID-19 infections may not produce symptoms. Therefore, simply screening for symptomatic individuals and having them isolate is not a broadly effective prevention strategy.9 Asymptomatic individuals still reproduce virus and could potentially infect others. Thus, recommendations that include the wearing of face coverings, maintaining a distance of at least 6 feet from others, and frequent hand hygiene are the focus of public health strategies to mitigate the spread of COVID-19 in the community.10,11
The CDC has developed numerous guidelines to prevent the spread of infection in all healthcare settings (Table 2). Infection prevention in dental care settings begins with standard precautions. Standard precautions apply to all body fluids, secretions, and excretions, except for sweat, regardless of the patient's known infectious status. Standard precautions are focused on strategies that will prevent DHCP from contacting potentially infectious body fluids of patients, such as the use of personal protective equipment (PPE).12
Contact transmission may be either direct or indirect. Examples of direct transmission are when microorganisms transfer directly from an infected individual to another person, such as when someone contacts an infected person's body fluids with an ungloved hand that has a cut or abrasion. Indirect transmission is when infectious material is transferred by a contaminated intermediate object or person.13 This includes diseases transmitted via healthcare worker's hands and the use of contaminated dental or medical instruments or devices.
Droplet transmission is technically a form of contact transmission. Rather than transferring from person to person via touch or a contaminated object or person, droplets transmission occurs with the infected respiratory droplets carrying infectious pathogens transmit infection when they travel directly from the respiratory tract of the infectious individual to susceptible mucosal surfaces of the recipient. Droplets are typically described as being >5 µm in size. Organisms transmitted by the droplet route do not remain infective over long distances, and therefore do not require special air handling and ventilation.13 COVID-19 is primarily transmitted by the droplet route, requiring strict adherence to the use of PPE to protect the mucous membranes of the face.1
Airborne transmission occurs when very small particles or droplet nuclei, which are desiccated droplets, are released. Because of their small size, these can travel over long distances and remain suspended in the air for a prolonged time.13 Because these small particles may enter the respiratory tract of exposed individuals and may be small enough to transfer through or around the open edges of a surgical mask, enhanced PPE is part of the recommended precautions for airborne diseases.
One of the most important changes in dental infection control during the COVID-19 pandemic has been an increased attention to PPE. Standard precautions for infection control for DHCP have long included the use of gowns, gloves, protective eyewear, and masks during dental procedures.12,14,15 Now, some elements of airborne precautions have been added during the pandemic for certain procedures.16
For procedures performed on patients not suspected or confirmed to be infected with COVID-19, DHCP should wear a surgical mask, eye protection, a gown or protective clothing, and gloves. This is consistent with standard precautions. In locations where there is moderate to substantial community transmission, DHCP are more likely to encounter patients with asymptomatic or presymptomatic infections and should add additional precautions.16 During aerosol-generating procedures, DHCP should use an N95 or better respirator.16 If a patient has symptoms or is confirmed to be infected with COVID-19, routine care should be delayed. If they must be treated, it may be necessary to provide care in an airborne illness isolation room (AIIR). Most dental facilities do not have AIIRs and the patient may need to be referred to a hospital equipped to treat patients with COVID-19. Employers must develop a respiratory protection program that includes medical evaluation, fit testing, and training when initiating the use of respirators.17Fit testing must be done when an employee initially and annually thereafter. During the COVID-19 pandemic, OSHA has temporarily waived the requirement for annual fit testing.18
Employees should receive training on when to use PPE, what PPE is necessary, how to properly don and doff PPE to prevent self-contamination, how to properly dispose of or disinfect and maintain PPE, and the limitation of PPE.16 In addition to enhanced PPE, there are also newer recommendations for the sequence of donning (putting on) and doffing (removing) the PPE (CDC dental interim). The suggested sequence is detailed in Figure 1.
Staying Motivated to Stay Safe
As the months of living with a pandemic drag on, many people are becoming weary with the interruptions and disruptions to normal life, sometimes called "pandemic fatigue." The World Health Organization (WHO) defines it as, "demotivation to follow recommended protective behaviours, emerging gradually over time and affected by a number of emotions, experiences and perceptions."19 The WHO goes on to explain, "at the beginning of a crisis, most people are able to tap into their surge capacity-a collection of mental and physical adaptive systems that humans draw on for short-term survival in acutely stressful situations. However, when dire circumstances drag on, they have to adopt a different style of coping, and fatigue and demotivation may be the result." As the impact of prolonged restrictions builds, including social, economic, emotional, and others, people can experience a shift in how they perceive the risk from the pandemic, resulting in relaxing precautions such as social distancing and mask wearing, despite rising cases in many locations.19
DHCP perform procedures that have been identified as high or very high risk.20 Despite the risks, they are not immune to pandemic fatigue. Acknowledging and discussing the very real emotional impact of living in a pandemic may be the first step to helping the dental team cope. While the WHO report focuses on what governments can do to ease pandemic fatigue, some of the same strategies should be effective for dental teams. These include discussion in several key areas, including (1) how individuals would like to implement recommended controls, (2) shifting from the attitude of "the pandemic controls our behaviors" to "our behaviors control the pandemic," (3) engage everyone in the development of policies related to COVID-19, (4) set goals and pledge to follow agreed upon behaviors, and (5) find effective ways to communicate that engage people.21
1. Centers for Disease Control and Prevention (CDC). Principles of Epidemiology in Public Health Practice, Third Edition. An Introduction to Applied Epidemiology and Biostatistics. Accessed October 10, 2020. https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section10.html.
2. Centers for Disease Control and Prevention (CDC). Scientific Brief: SARS-CoV-2 and Potential Airborne Transmission. Accessed October 11, 2020.https://www.cdc.gov/coronavirus/2019-ncov/more/scientific-brief-sars-cov-2.html.
3. 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;382(16):1564-1567. doi: 10.1056/NEJMc2004973. Epub 2020 Mar 17. PMID: 32182409; PMCID: PMC7121658.
4. Centers for Disease Control and Prevention (CDC). Accessed October 5, 2020. How COVID-19 Spreads. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/how-covid-spreads.html.
5. Anderson EL, Turnham P, Griffin JR, Clarke CC. Consideration of the aerosol transmission for COVID-19 and public health. Risk Anal. 2020;40(5):902-907. doi: 10.1111/risa.13500. Epub 2020 May 1. PMID: 32356927; PMCID: PMC7267124.
6. Cai J, Sun W, Huang J, et a. Indirect virus transmission in cluster of COVID-19 cases, Wenzhou, China, 2020. Emerg Infect Dis. 2020;26(6):1343-1345. doi: 10.3201/eid2606.200412. Epub 2020 Jun 17. PMID: 32163030; PMCID: PMC7258486.
7. Alsved M, Matamis A, Bohlin R. Exhaled respiratory particles during singing and talking. Aerosol Science and Technology. 2020;54(11):1245-1248. doi:10.1080/02786826.2020.1812502
8. Morawska L, Cao J. Airborne transmission of SARS-CoV-2: the world should face the reality. Environ Int. 2020;139:105730. doi: 10.1016/j.envint.2020.105730. Epub 2020 Apr 10. PMID: 32294574; PMCID: PMC7151430.
9. Luo L, Liu D, Liao X, et al. Contact settings and risk for transmission in 3,410 close contacts of patients with COVID-19 in Guangzhou, China: a prospective cohort study. Ann Intern Med. 2020 Aug 13. doi: 10.7326/M20-2671. Epub ahead of print. PMID: 32790510.
10. Centers for Disease Control and Prevention (CDC). Considerations for Wearing Masks. Accessed October 11, 2020. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/cloth-face-cover-guidance.html.
11. Centers for Disease Control and Prevention (CDC). How to Protect Yourself and Others. Accessed October 11, 2020. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html.
12. Kohn WG, Harte JA, Malvitz DM, et al. Guidelines for infection control in dental health care settings--2003. J Am Dent Assoc. 2004;135(1):33-47. doi: 10.14219/jada.archive.2004.0019. PMID: 14959873.
13. Siegel JD, Rhinehart E, Jackson M, Chiarello L; Health Care Infection Control Practices Advisory Committee. 2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Health Care Settings. Am J Infect Control. 2007;35(10 Suppl 2):S65-164. doi: 10.1016/j.ajic.2007.10.007. PMID: 18068815; PMCID: PMC7119119.
14. Center for Disease Control and Prevention (CDC). Recommended infection-control practices for dentistry. MMWR Morb Mortal Wkly Rep. 1986;35(15):237-42. PMID: 3083228.
15. Recommended infection-control practices for dentistry, 1993. Centers for Disease Control and Prevention. MMWR Recomm Rep. 1993 May 28;42(RR-8):1-12. PMID: 8502212.
16. Centers for Disease Control and Prevention (CDC). Interim Infection Prevention and Control Guidance for Dental Settings During the Coronavirus Disease 2019 (COVID-19) Pandemic. Accessed October 11, 2020. https://www.cdc.gov/coronavirus/2019-ncov/hcp/dental-settings.html
17. Occupational Health and Safety Administration (OSHA). Respiratory Protection. OSHA 3079. Accessed September 6, 2020. https://www.osha.gov/Publications/osha3079.pdf.
18. Occupational Safety and Health Administration (OSHA). Temporary Enforcement Guidance - Healthcare Respiratory Protection Annual Fit-Testing for N95 Filtering Facepieces During the COVID-19 Outbreak. Accessed September 6, 2020. https://www.osha.gov/memos/2020-03-14/temporary-enforcement-guidance-healthcare-respiratory-protection-annual-fit.
19. World Health Organization, Regional Office for Europe. Pandemic fatigue - reinvigorating the public to prevent COVID-19. Policy framework for supporting pandemic prevention and management. 2020. https://apps.who.int/iris/bitstream/handle/10665/335820/WHO-EURO-2020-1160-40906-55390-eng.pdf.
20. Occupational Health and Safety Administration (OSHA). COVID-19 Control and Prevention. Dentistry Workers and Employers. Accessed October 11, 2020. https://www.osha.gov/SLTC/covid-19/dentistry.html
21. Habersaat KB, Betsch C, Danchin M, et al. Ten considerations for effectively managing the COVID-19 transition. Nature Hum Behav. 2020; 4(7):677-687. doi: 10.1038/s41562-020-0906-x. Epub 2020 Jun 24. PMID: 32581299.