Universal precautions in health care settings, Face Shields, Transmissibility
As we move into colder weather months we wanted to take a moment to review what we have learned so far about the transmission of SARS-CoV-2 and what factors increase transmission. It appears that the most important factors are physical distance and duration of contact. Also important is whether the setting is indoors or outdoors (essentially all “super-spreading” events have occurred indoors), viral load of the infected person, and susceptibility of the host. Regardless, all of these variables highlight the importance of universal precautions. A meta-analysis from the WHO published in The Lancet back in June investigated the effects of physical distance, face masks, and eye protection on virus transmission in healthcare and non-healthcare settings (https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)31142-9/fulltext). They found that transmission of SARS-CoV-2 was lower with physical distancing of > 1 meter (and protection was increased when the distance was lengthened), with the use of face masks and eye protection. As we have mentioned in earlier issues of COVID-19 Corner, all Cleveland Clinic employees working in patient-facing areas are required to wear face shields over surgical masks. What do these face shields do for us? They do several things: provide eye protection, provide a second later of protection for the mucous membranes of the mouse and nose, they help prevent self-inoculation and facilitate extended use of face masks. In a 2014 study using a coughing patient simulator and influenza-laden cough aerosols, wearing a face shield reduced inhalation of large droplets by 96% and reduced large droplet surface contamination of the underlying mask by 97% (https://pubmed.ncbi.nlm.nih.gov/24467190/). Use of goggles in lieu of a face shield (if you have worn a face shield – not the most comfortable) is permissive, but the data favor face shields. The key takeaways here are that universal pandemic precautions decrease exposure to SARS-CoV-2, including in the healthcare setting. As flu season approaches, these universal precautions will also decrease exposure to other respiratory viruses, including influenza, which we hope will lead to a more mild flu season, as the Southern Hemisphere has experienced so far.
We encourage you to check out this comprehensive review of the evidence on transmission of SARS-Co-V-2, written by Paul Sax and colleagues, and published in the Annals of Internal Medicine last week (https://www.acpjournals.org/doi/10.7326/M20-5008). They review the question of whether or not one can become infected with SARS-CoV-2 from fomites, and the short answer is that while direct contact and fomite transmission are likely possible they are not a common mode of transmission. Regarding other modes of transmission, while transplacental transmission has been documented, vertical transmission has been reported only very rarely. While live virus has been isolated from stool, and viral RNA from semen and blood, to date there have been no reported cases of SARS-CoV-2 transmission via fecal-oral, sexual or blood-borne routes. The main mode of transmission is via respiratory droplets.
Timing of exposure is another important risk factor in transmission of SARS-CoV-2 and there appears to be a “period of infectiousness” during which the risk of transmission is higher. We know that those infected with SARS-CoV-2 with or without symptoms can transmit virus. Studies have shown that transmissibility peaks around 1 day before symptom onset and then declines rapidly over 7 days, as viral loads in the respiratory tract decrease quickly after symptom onset. Patients with severe disease have higher respiratory viral loads compared to those with more mild cases, although viral loads decline with time regardless. While virus can be detected via PCR long after symptom resolution there is a growing amount of data showing that beyond 8 days this is not a cultivatable virus (while this period may last longer in severely ill patients hospitalized with COVID). As we have mentioned in previous issues, for these reasons our institution has moved away from the testing method for return to work or ending isolation of infected patients and healthcare workers, and a symptom-based strategy is preferred by the CDC.
There is much more to discuss but we will leave you with this: continue to maintain best practices during the pandemic, wear your mask, social distance, make smart decisions when not at work, and most importantly, it is our duty to council our patients to do the same. And perhaps most importantly – get your flu shots and give your patients flu shots!
Shout out with any questions or comments, or anything you’d like to read about in future issues of COVID-19 Corner
Shout out with any questions or comments