CDC has stated the identification of a close contact should not consider whether the individuals are wearing masks. Is there evidence of transmission of COVID at the workplace when both COVID case and the co-worker are wearing protective masks ? or conversely of protection by masks at the workplace? This would not include the healthcare setting of caring for COVID patients.

The CDC’s advice to not consider whether individuals were wearing masks when determining if a Close Contact had occurred should not be misinterpreted to imply that masking does not substantially decrease the person to person transmission of the SARS-Co-V-2 virus (the Virus).  Furthermore, limited data exists regarding workplace transmission of the Virus, and inherent variations between worksites and workforces necessitates caution when making comparisons between industries and employers. The CDC and other respected public health groups strongly recommend universal mask wearing, and the currently available data, as well as our understanding of particle science, strongly supports this recommendation.1
 
Evidence now exists  that environments where masks are not universally used have higher rates of COVID-19 transmission, and environments where masks are universally required have lower rates of transmission especially when both individuals involved in a Close Contact were wearing masks.  Additionally, as our understanding surrounding the mechanism of transmission of the Virus has evolved from that of large respiratory droplet to that of large and small (i.e. aerosol) respiratory droplet transmission, substantial evidence from the particle science community supports the biologic plausibility for the efficacy of mask use for both those wearing the mask and those surrounding mask wearers from airborne pathogens, especially when masking is universally used by all individuals involved in an interaction.
 
A September 11, 2020 MMWR article described the relative risk of contracting COVID-19 in different settings in the United States during July 2020.  The highest risk environments included restaurants, bars/coffee shops, gyms, and church/religious gatherings.2  These environments were noted to be places where mask use and social distancing were difficult to maintain.
 
A July 17, 2020 MMWR described the lack of transmission of the Virus from two infected hair stylists when a universal face covering policy was implemented in Springfield, Missouri during May 2020.  Among 139 clients exposed to two symptomatic hair stylists with confirmed COVID-19 while both stylists and clients wore face masks, no symptomatic secondary cases were reported.3
 
A workshop focused on airborne transmission of the Virus organized by the National Academies of Science, Engineering, and Medicine in August 2020, provided the mechanistic evidence for universal masking at this time.  Studies estimate that surgical masks reduce aerosol emissions of influenza from the source by 67%-75% and reduce intake by 50%-83%.  Others have shown masks or face coverings can reduce aerosol and droplet emission at the source by 52%-90% depending on mask type, fit, and use.  Masks also reduce wearer intake of aerosols and droplets by 25%-90%.  Furthermore, masks reduce jet propagation of respiratory plumes, limiting the distance traveled by droplets and aerosols in the plumes.  Despite the data to support the protective value of masks, the fact that not all masks provide the same protective value, and the variation in the way masks are worn, will create additional confounders as we continue to study the transmission of the Virus.4
 
The information above combined with our observations from Asian countries  where mask usage is almost universal, despite numerous confounders, argues for the universal wearing of face masks in public and the workplace.
 
Despite the current body of information in support of universal masking, we still have much to learn. While recommendations currently exist regarding the characteristics of an effective mask and proper usage, a universal certification for different types of masks does not currently exist.  We still do not know the minimum dose of Virus required to cause disease, nor the potential variation in susceptibility from person to person of acquiring infection.  Current estimates suggest that over 40% of those infected with COVID-19 are asymptomatic, and these individuals are capable of transmitting disease.  Current studies have shown for those with symptomatic COVID-19, the period of highest viral shedding and thus infectivity occurs at symptom development or shortly before.  In light of the above, mask wearing while in the public and at work  should be considered universal precautions analogous to the use of barrier gloves for the prevention of blood borne pathogens.  Mask wearing is one important layer in the mitigation efforts for COVID-19 and should not be considered to eliminate all of the risk of transmitting or acquiring COVID-19.  Additional layers of mitigation for COVID-19 should include hand and surface hygiene, social distancing, maximizing indoor air quality, accurate and accessible testing, and contact tracing with recommended periods of isolation and quarantine based on current knowledge.
 

Citations

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Disclaimer:
The Forum does not necessarily represent an official ACOEM position. The Forum is intended for health professionals and is not intended to provide medical or legal advice, including illness prevention, diagnosis or treatment, or regulatory compliance. Such advice should be obtained directly from a physician and/or attorney. Questions are answered with the best available data or recommendations at the time. 

  1.  CDC Partner Update from 10/5/20: Wear it Don't Share It - The Art and Science of Cloth Masks, https://www.youtube.com/watch?v=iutetOVWJxg.
  2.  Community and Close Contact Exposures Associated with COVID-19 Among Symptomatic Adults ≥ 18 Years in 11 Outpatient Health Care Facilities - United States, July 2020; MMWR, September 11, 2020, 69(36);1258-1264. https://www.cdc.gov/mmwr/volumes/69/wr/mm6936a5.htm.
  3.  Absence of Apparent Transmission of SARS-CoV-2 from Two Stylists After Exposure at a Hair Salon with a Universal Face Covering Policy – Springfield, Missouri, May 2020; MMWR, July, 17, 2020, 69(28);930-932. https://www.cdc.gov/mmwr/volumes/69/wr/mm6928e2.htm.
  4. Airborne Transmission of SARS-Co Proceedings of a Workshop-In Brief; National Academy of Science October 2020, p 8. https://www.nationalacademies.org/our-work/airborne-transmission-of-sars-cov-2-a-virtual-workshop.