Study: combination of PPE and HEPA filtration offers health workers best Covid protection

A Monash University study has demonstrated that full PPE, with a fit-tested N95 mask, in conjunction with a HEPA filtration system, offers health workers the best protection against virus aerosol exposure.

The study was led by Dr Simon Joosten, from the Monash University School of Clinical Sciences, and co-funded by the Monash Institute of Medical Engineering and Monash Partners Academic Health Science Centre.

It used a live virus aerosol model and highlighted the fact that the standard PPE strategy that was developed with droplet transmission in mind is not geared to prevent aerosol transmission and may offer insufficient protection in a healthcare environment, namely a hospital setting in this case.

Studying the interaction of virus aerosol and PPE, the research found that the installation of a HEPA filter that cleans the room volume 13 times an hour, combined with a fit-tested N95 mask and full PPE, offered almost complete prevention of nasal contamination by live virus aerosol.

The experimental study reportedly used a nebuliser to pump bacteriophage PhiX174 into a sealed clinical room for 40 minutes, testing three scenarios:

●     A health care worker in full PPE: surgical mask, gloves, gown, face shield.

●     A health care worker in full PPE: but with a fit-tested N95 mask.

●     A health care worker in full PPE: with a fit-tested N95 mask and a HEPA filter system.

Virus exposure was then captured via skin swabs applied to the face, nostrils, forearms, neck and forehead.

It found significant infiltration in scenario one (more than 200 virus particles detected in nostril), slightly less infiltration in scenario two (between 25-200 virus particles detected in nostrils) and almost complete prevention in scenario three (zero to one virus particle detected).

Quantitative fit-testing of masks is carried out by hospital respiratory protection programs and involves a quick test to measure how much air is being filtered by the mask, as opposed to leaking through the sides using a machine that tests for leaks. This ensures that the right mask with the best fit can be chosen by staff on the ward.

While this research is currently under peer review, the findings, when presented to hospital management at Monash Health and Epworth Health, resulted in immediate impact with Dr Joosten involved in helping both health services deploy HEPA filter technology on hospital wards caring for Covid-19 patients.

Dr Joosten says the findings demonstrate that standard PPE alone does not protect against infectious aerosol at high load.

“Our study highlights the need to provide multiple layers of protection to health care workers during the Covid-19 pandemic,” says Dr Joosten.

“Among the most important protective measures are vaccination, personal protective equipment and ventilation.

“Here we show that personal protective equipment and ventilation interact to provide added protective benefit against virus-laden aerosol.”

Monash Health Chief Medical Officer, Professor Anjali Dhulia, says Dr Joosten’s previously published and most recent HEPA filter data research contributed to the deployment of HEPA filter technology at Monash Health.

“Dr Joosten continues to provide ongoing input to Monash Health in this space given his research expertise,” says Professor Dhulia.

Dr Lachlan Henderson, Group Chief Executive, Epworth HealthCare, says keeping patients, staff and doctors safe has been the priority throughout the pandemic.

“Epworth has been a leader in implementing a higher level of PPE than was required across key areas like our emergency departments, intensive care units and Covid-19 ward,” says Dr Henderson.

“We have also regularly reviewed airflows at each of our hospitals. Dr Joosten’s virus aerosol research was critical in guiding our infection control team to deploy HEPA filter technology at Epworth as an added layer of protection.”