What I learned from the 2nd ISIAQ webinar on Spread of Infectious Diseases in Indoor Environments

ISIAQ, the International Society of Indoor Air Quality and Climate is an international, independent, multidisciplinary, scientific, non-profit organization “whose purpose is to support the creation of healthy, comfortable and productive indoor environments.” The ISIAQ Board of Directors and The Academy of Fellows are hosting a webinar series on the spread of COVID-19 and infectious diseases in indoor environments. What an excellent idea and I look forward to the upcoming webinars.

The webinar on April 7 was given by Dr. Maosheng Yao, Peking University, titled: “Aerosol and Breath Transmission of SARS-CoV-2 Virus.”  Below are my notes and what I learned from this webinar.

Summary of the talk: airborne SARS-CoV-2 transmission is very likely playing an important role in current COVID-19 pandemic in indoor environments. However, the air is relatively safe for most open space or well-ventilated environments. Wearing a masks and sufficient ventilation in public places are the key to containing the pandemic, social distancing is also very important to fight against COVID-19.

Xu, Wu and Yao, 2017 studied fluorescent bioaerosol emission rates of human exhaled breath from 12 healthy subjects in a controlled environment (27 m3) (used the UV-APS that detects viable biological aerosol particles).  They also evaluated the emission when they were wearing a doctor mask and N95.  The mode of the exhaled particle size distribution was 1.5 microns, with no particles greater than 3 microns. (This was also confirmed later in classroom observations with 100 students.) Five people not wearing masks increased the bioaerosol concentration by 107% within 30 min; exhaled breath bioaerosol emissions accounted for about 17% of the particle increase (the rest is skin, clothing, resuspension).

Fan et al. 2017 measured Beijing subway human bioaerosol emissions and found that they increased at peak rush hour (3x higher compared to off peak) around 1 micron, and not many droplets > 5 microns were detected.

Yao’s group developed rapid flu diagnosis methods (Shen et al. 2012) to collect breath condensate and were able to detect influenza A viruses down to 29 viruses/micro-L in clinical exhaled breath condensate (EBC) samples within minutes.

Zheng et al. 2018: In this paper, they were able to detect bacterial pathogens (H. Influenzae and MRSA) in EBC; and EBC and throat samples agreed from 35-65%.

Dr. Yao is conducting both high volume sampling and low volume sampling in hospitals. Note that similar to other recent papers, semi-closed environments appear more concerning for possible airborne transmission. Additional work in progress is EBC sampling to try and detect SARS-CoV-2 using above mentioned methods (which is both dangerous and difficult!). Also working on analyzing surface swabs and finding SARS-CoV-2 on some hospital surfaces…(papers forthcoming!)

Pyankov et al. 2018 studied MERS virus aerosol survival and showed that inactivation was more efficient at high air temperature and low relative humidity. Note that during the webinar there was some discussion of whether absolute humidity would be a useful metric as well given that transmission is occurring in indoor environments.

Yao also discussed air quality impacts on microbial aerosols including flu, and cited this paper: Zhang et al. 2019 and this paper: Ali et al. 2018.

Webinar highlights and Presenter bio.