Webinar – Dr Simon Joosten on why we need HEPA filtration

Table of Contents

Doctor Simon Joosten has been working on COVID wards in large Melbourne hospitals since the beginning of 2020 and presents research conducted over the course of 2020 and 2021 that influenced both the Victorian Government, Epworth Health and Monash Health to purchase HEPA filters. The presentation is pared down to the research that changed people’s minds about the use of HEPA filters.

Firstly, the CDC and WHO defined SARS and COVID modes of transmission to include aerosols only in early 2021, April 30 for the WHO, and May 7 for the CDC. At that point the pandemic had been present for over a year, so the official inclusion of aerosol transmission was extremely late. Infectious Disease Control groups also were belated from the time of onset in recognising the way this disease was being spread. Eventually it was realised that one of the biggest aerosol generators in hospital settings were the patients themselves. People make aerosol wherever they go, and the amount exposure is dependent on proximity, shared air and whether or not air is pumping through that person’s lungs.

Many hospitals are designed for comfort and temperature, often they are old buildings with poor ventilation and with windows that don’t open. Patients are cared for in wards and shared spaces like an open plan office, usually in older hospitals where there are up to four patients in a single space with no intervening wall.

When there are thousands of people with COVID existing levels of supply do not suffice, and other methods and environmental solutions are needed to mitigate the spread. At the start of the pandemic, it quickly became clear that to rebuild a whole hospital infrastructure would not be possible. The prime goal in a hospital space is to protect patients in that space who are not able to wear protective equipment. The requirement is that all workers should be wearing high grade protective equipment; in particular, gloves, face shields and fitted N 95 masks.

To address this transmission rate in hospital environment the first solution was to optimise personal protective equipment, a strategy that is not wholly palatable for businesses, but in hospitals is vitally important.

The second solution was to optimise ventilation or environmental issues which is now a priority in the area of transmission mitigation in both CDC and WHO documents. This demonstrates that cheap and easily up-scalable technology can be used to enhance the effect of PPE.

Goal: quantifying levels of risk of aerosol infection

Method of Testing:

  1. Live virus Phi X174 (non-harmful to humans, used to kill e. coli) nebulised into a space to simulate Covid expulsions
  2. Aerosol streams measured
  3. Agar plates with e. coli show where Phi X174 is present
  4. PPE and nose/body is swabbed to quantify how much virus is present, with and without a HEPA filter.


Graphs showed the effects of the HEPA filter, and the key outcome was that with a surgical mask and a HEPA filter, counts were still noted from inside the nostril.

A fitted N95 mask with a HEPA filter showed counts at almost zero, concluding that the HEPA filter enhances the effect of a N95 mask. The four key findings of the research are:

  1. No combination of mask and PPE will prevent significant skin and upper airway contamination at high virus aerosol load.
  2. Combining a fit tested N 95 mask with the use of an air filter provides almost complete protection for healthcare workers against skin and upper airway contamination.
  3. When using a mask, it must be fit tested and a N 95 mask, but it cannot be used alone.
  4. The mask must be combined with adequate ventilation strategies in the experimental setup studied..

Health services need to provide extensive quantitative fit testing programs for mask wearing, and perhaps businesses, and also optimise strategies that address ventilation and environmental issues. Once COVID reaches pandemic proportions, environmental management becomes paramount.


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