Virus Transmission in Schools

Seeing the progression of the fourth wave and the current occurrences of COVID-19 outbreaks, I decided to bring up the topic of COVID-19 transmission in schools.

In Quebec, our national institute of public health (INSPQ) is nothing to laugh at. They kept track of all outbreaks ever since the beginning of the pandemic and do an amazing job of giving free access to that data. What’s particularly interesting is when you look at occurrences of COVID outbreaks in Quebec; most COVID-19 cases are reported mainly in 3 types of environments: workplaces, healthcare and long-term care facilities, and schools1.

Many people have already covered that SARS-CoV-2 is airborne (Justin Morgenstern MD did a pretty good review on this topic)2. The fact that outbreaks occur in these above-mentioned environments is yet but another cue in favor of airborne transmission, as these are all indoor spaces. Furthermore, schools in Quebec are not known for their state-of-the-art ventilation systems; most of them are old and weren’t built with centralized ventilation and heating systems. Many of the workplaces where outbreak occurs also have inexistent, derelict or underperforming ventilation systems.

Also, most health instances around the world have recognized that ventilation plays a role in SARS-CoV-2 transmission, and that transmission risk is higher in indoor spaces. Thus, ventilation and indoor air quality are most definitely critical to reduce the risk of exposure in indoor spaces.

Here is an interesting report of the impact of various public health measures that were implemented in different Georgian schools at the end of last year (Nov-Dec 2020).

The results of the reports demonstrated that ventilation strategies are associated with a lower incidence of COVID-19 cases in K5 schools (kindergarten to grade 5). Additionally, utilizing air filtration/air disinfection portable devices, equipped with either/or HEPA filtration and UVGI (Ultraviolet Germicidal Irradiation) is also associated with a decreased incidence in COVID-19 cases compared to school without such systems. Combination of ventilation and air purification has been associated with a whopping 48% reduction of the incidence of COVID-19(!).

I’d say that these results are eloquent in demonstrating that ventilation, but also air disinfection, are effective measures to reduce the risk of COVID transmission in indoor spaces.

Considering that Sanuvox units have been shown to effectively deactivate SARS-CoV-2 (as UVGI is effective against any biological pathogens), it is questionable that such an easy risk mitigation measure is still doubted to be effective. Especially since the INSPQ has recommended the use air purification devices to prevent tuberculosis in indoor spaces3, which has undoubtedly been shown to be an airborne-transmitted disease…

 


 

1 https://www.inspq.qc.ca/covid-19/donnees/eclosions

2 https://first10em.com/covid-is-airborne-a-brief-update/

3 https://www.inspq.qc.ca/sites/default/files/publications/1948_mesures_prevenir_micobacterium_tuberculosis.pdf

 


 

Summary of a report by the Center for disease control and prevention (CDC) on the impacts of mask mandate and ventilation improvements on COVID-19 transmission rates in elementary schools (Georgia, USA)

Mask Use and Ventilation Improvements to Reduce COVID-19 Incidence in Elementary Schools — Georgia, November 16–December 11, 2020
https://www.cdc.gov/mmwr/volumes/70/wr/mm7021e1.htm?s_cid=mm7021e1_w

Figure 1

Figure 1. Impacts of ventilation improvement in elementary schools as a prevention strategy for COVID-19. During the period from November 16 to December 11 2020, data was collected from K-5 schools (kindergarten to grade 5) in Georgia (USA), following the implementation of different recommended prevention strategies for COVID-19. A total of 169 schools in Georgia completed the study and had COVID-19 case data. Out of 169 schools, 123 schools were selected from reporting having knowledge on ventilation improvements taken. Ventilation strategies included opening windows and doors, as well as using fans (dilution), or using filtration methods (HEPA) with or without air purification (UV germicidal irradiation, UVGI). Data is presented as an adjusted rate ratio, which is a measure reporting the incidence of COVID-19 cases occurring at any point in time, compared to control (No ventilation improvement).

 

Figure 2

Figure 2. Impacts of the application of mask mandate in elementary schools as a preventive measure against COVID-19 transmission.  During the period from November 16 to December 11 2020, data was collected from K-5 schools (kindergarten to grade 5) in Georgia (USA), following the implementation of different recommended prevention strategies for COVID-19. A total of 169 schools in Georgia completed the study and had COVID-19 case data. Prevention strategies varied from school to school, with 65,1% requiring masks for teachers and staff members, but only 51,5% schools requiring mandatory masks for students. Data is presented as an adjusted rate ratio, which is a measure reporting the incidence of COVID-19 cases occurring at any point in time, compared to control (optional mask requirement).


Make sure to read this related press release:

Limitations of CO2 measures as an indicator of indoor air quality

Resume of a publication by the National Collaborating Centre for Environmental Health (NCCEH)
‘’Can CO2 sensors be used to assess COVID-19 transmission risk?’’.

https://ncceh.ca/content/blog/can-co2-sensors-be-used-assess-covid-19-transmission-risk

  • Carbon dioxide (CO2) is monitored to assess air quality and adequate ventilation indoors
    • Human activity indoors increase levels of CO2
    • CO2 measures are also used as an indicator for hard-to-detect volatile organic compounds (VOC) and microorganisms
    • Ventilation settings are then calculated accordingly to prevent CO2 buildup, and also reduce exposures to potentially harmful compounds and pathogens

 

  • Indoors CO2 acceptable standards has been arbitrarily established at around 1000 ppm
    • Nonetheless, recent reviews have failed to demonstrate a clear link between increasing CO2 concentration and lower reported quality of air and associated symptoms1
    • Furthermore, a study has shown that CO2 linked to human activity had effects on perceived air quality and cognitive impairment, but that pure CO2 at the same concentration did not have these effects, suggesting that something else related to human activity (breathing, talking) was responsible for the symptoms reported2

 

  • Thus, CO2 measures might not be an adequate indicator of airborne biological contaminants, such as bacteria and viruses:
    • Historically, many studies have demonstrated a link between adequate ventilation (as per CO2 levels) and lower transmission of airborne diseases.
    • Yet, multiple factors can affect CO2 emissions and have little to no effect on increasing airborne microbial count.
      • Animals and other living beings
      • Combustion devices
    • Also, some factors can increase or decrease the airborne charge of biological contaminants, but have no effect on CO2 emissions
      • Superspreaders; People that emit high charges of airborne pathogens, but don’t produce more CO2
      • Singing and talking has been linked to an increase in emission of viral particles
      • Wearing a mask reduces the emission of airborne bio-contaminants, but has no effects on CO2 production
      • Air disinfection and filtration have no effect on CO2 levels but reduce airborne particle charge

 

In summary, even though CO2 measures and monitoring can be installed at low cost and used to evaluate ventilation, it might not be an adequate measure of the risk of exposure to airborne pathogens (such as SARS-CoV-2). It does, however, helps to educate the public about the importance of improving ventilation and indoor air quality (IAQ).


1 https://eta-publications.lbl.gov/sites/default/files/ashrae_journal_-_september_2019_76_-_77.pdf
2 https://onlinelibrary.wiley.com/doi/abs/10.1111/ina.12284