ECOH News

Control COVID Transmission at Holiday Gatherings

April 6, 2022

Another holiday weekend is approaching, and COVID-19 rates are increasing, largely due to the highly infectious BA.2 subvariant of Omicron. Going into the third spring of the pandemic, many of us are wondering how to prevent transmission as we gather to celebrate seasonal festivities.

It’s not easy, but it can be done. Below are some ways you can lower infection risks when you get together with family and friends.

Use Multiple Layers of Protection

The “swiss cheese” model, first suggested by safety expert James Reason, has been widely adapted for the COVID-19 pandemic to illustrate that there is no single silver bullet for preventing infection. We need to use a variety of strategies to minimize risk – every little bit helps. If the virus figuratively gets through a hole in one slice of cheese, it can be blocked by subsequent layers.

Multiple layers Improve success

Reduce the likelihood that someone infected will be present

You want to do all you can before your event to make sure that an infected person will not attend your event Remember that COVID can be contagious even when someone does not have symptoms.  This will be easier if your guests understand some conditions for attending.  It is not always easy to ask family and friends to abide by rules, but it may be more acceptable if you are clear that this applies to everyone.  These conditions can include:

  1. Ensure that all those eligible have been fully vaccinated and boosted.
  2. Ask everyone to take a rapid test just before coming to your event. Rapid tests are not 100% accurate in detecting infection, but they are one more thing that can help lower risk.  Ontario Health has new guidance about swabbing your throat and nose to get the most accurate results possible. 
  3. Ask that people agree not to attend if they may have been exposed to someone with COVID, or if they are experiencing any COVID symptoms.
  4. Keep your gatherings small. The fewer people present, the lower the chances that someone will be infected, and the easier it will be to maintain physical distances. If you have a large family or friend group, consider holding your celebrations with smaller groups in different places, and have the groups meet up electronically for part of the event.

Control Airborne Spread

It is now widely accepted that SARS-CoV-2, the virus that causes COVID-19, can be transmitted through the air.  Infectious aerosols can be emitted when an infected person breathes, talks, sings, coughs, or sneezes, and another person can be infected if they inhale these aerosols. The risk of infection increases greatly in indoor settings where infectious aerosols can accumulate in the air to a critical concentration.

The risk of transmission is much lower outdoors – so, if possible, hold your event outdoors and maintain physical distance between people not in the same household.

If your event is indoors, ensure the best ventilation possible through the following measures:

  1. Open windows
  2. If possible, use filters with a high filtration rating in your home ventilation system. If the system can accommodate it, filters with a MERV rating of 13 or more are recommended. (MERV stands for Minimum Efficiency Rated Value and is a filter rating system.)  Check with someone knowledgeable about your system before installing higher-rated filters because they won’t work in all systems.
  3. If your ventilation system uses a fan that normally goes on and off based on temperature, set it so that it is running all the time while people are visiting.
  4. Run kitchen and bathroom exhaust fans continuously if they are not too noisy. If you do this, make sure you have some windows open to supply enough make-up air.
  5. Aim for a total of at least 6 air changes per hour from all sources.  If you cannot achieve that through open windows and your home ventilation system, consider a portable air cleaner (HEPA unit).

Links to various resources have been provided at the end of this blog to help you assess your ventilation and choose an appropriate portable air cleaner.   

Avoid Transmission Through Close or Direct Contact

Transmission by fomites (contaminated surfaces or objects) is not believed to be as important as was thought when the pandemic started.  But it’s still a good idea to reduce risk by avoiding the possibility of touching contaminated objects.

 In addition, physical distancing rules recommended since the start of the pandemic are still good advice – transmission is much more likely at close contact.

To reduce risk as much as possible, we should continue to prevent the possibility of transmission through these routes. Therefore:

  1. Maintain physical distance from people in different households as much as possible. If you have a small gathering and a table with adjustable size, open up the table to its largest size to allow the greatest possible distance between households.
  2. Try to avoid people from different households working in the kitchen at the same time. If guests are bringing food, it should not require on-site preparation. 
  3. Serve food in a way that minimizes the need to pass dishes around to many people. For example, serve food on separate serving dishes for each household group.
  4. Wearing a good face-covering/respirator is effective in preventing transmission but may not be feasible if your gathering involves eating and drinking. But it is a good idea to wear one when you are in close contact with others and not eating/drinking.  Use one with good fit and filtering properties like an N95 or equivalent and conduct a seal check to make sure it fits well.
  5. Of course, good hygiene practices including hand washing/cleaning must be observed by everyone!

Ventilation Resources

  1. ECOH webinar – explains concepts of aerosol transmission and good ventilation https://www.ecoh.ca/mitigating-airborne-transmission-with-effective-ventilation-strategies-webinar/
  2. OHCOW tool – explains and provides a spreadsheet tool for assessing ventilation. Designed for classrooms but works for other spaces too. https://www.ohcow.on.ca/covid-19/ventilation-calculation-tool/
  3. Clean air crew – good information on assessing ventilation and sourcing portable air cleaners https://cleanaircrew.org/ventilation/, including information on how to make a Corsi-Rosenthal box, a do-it-yourself inexpensive effective air cleaner, https://cleanaircrew.org/box-fan-filters/

ECOH wishes you a happy, healthy spring holiday!  If you need our help with COVID controls or other health and safety needs, please contact us.

Marianne Levitsky, MES, CIH, ROH, FAIHA

Senior Industrial Hygiene Associate

Marianne Levitsky is a Certified Industrial Hygienist/Registered Occupational Hygienist and a Senior Industrial Hygiene Associate at ECOH, where she has been involved in developing ECOH’s COVID-19 response and advising clients on re-opening plans. She was founding President of Workplace Health Without Borders, a non-profit organization that engages volunteers in promoting occupational health for workers everywhere. She was previously Director, Best Practices, Prevention for the WSIB and an occupational hygienist with the Ontario Ministry of Labour. She is adjunct faculty at the University of Toronto and was a member of the Toronto Board of Health. Marianne has received the OHAO Hugh Nelson award and the Yant Award from AIHA, both of which recognize excellence in occupational hygiene. She has served as chair of the AIHA International Affairs Committee and is an AIHA Fellow.

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