Dear member / clinic,

The current Delta outbreak is again highlighting the significance of airborne transmission of SARS-CoV-2.

We have mentioned air filtration in an earlier email, but would like to highlight additional recent evidence that portable HEPA air purifiers can remove up to 99% of airborne viral particles and significantly reduce the risk of airborne viral transmission in enclosed spaces. We recommend clinics consider HEPA air purifiers as an adjunct to other ventilation strategies.

Such air purifiers are already being used in at least one UCC in NZ and EDs in Australia. They’re reasonably inexpensive, and some model suggestions and desired characteristics are supplied below; please refer in particular to this Harvard spreadsheet which includes a tool for calculating the performance needed for different size spaces, frequency of filter changes, and an analysis of the performance of different models. Please note the spreadsheet has three tabs.

It is vital for Urgent Care Clinics to have a multi-layered approach to minimise the airborne spread of Covid-19 within their facilities, including, per our earlier advice:

  • Red and green streaming of patients
  • Assess respiratory patients in separate areas and preferably outside the clinic
  • Minimise the length of stay of at risk patients in the clinic
  • Telemedicine and bookings, where practicable
  • Assess the adequacy of the building’s ventilation system and improve ventilation by opening windows and doors where possible, and utilising portable HEPA air cleaners.
Evidence and more detailed recommendations on HEPA air purifiers and measures against airborne transmission are linked here and copied below.

With best wishes,

David Gollogly, Jasmine Mackay, Richard Chen, Kelvin Ward
Pandemic Response Subcommittee

Airborne transmission is now widely recognised as the dominant mode of transmission of SARs-CoV-2. Nosocomial infection in healthcare settings was recognised early in the pandemic between patients in GP waiting rooms in Italy, and closer to home to healthcare staff during the Victorian outbreak in mid 2020. Consequently GPs in New Zealand moved predominantly to virtual consultations during the March 2020 and August 2021 Level 4 lockdowns.
Urgent Care Clinics, by their very nature remain open for face-to-face consultations for patients with acute medical conditions and accidents. Therefore clinics must mitigate indoor airborne transmission when there is a clinical need to have patients inside the building, using a multifaceted approach.

Recommendations to reduce the risk of airborne transmission

  • Opening windows to improve natural ventilation
  • Adding HEPA air purifiers within the clinic.

Evidence for the use of HEPA air purifiers

  • A recent study in Melbourne demonstrated that “With 2 small domestic air cleaners in a single patient room of a hospital ward, 99% of aerosols could be cleared within 5.5 minutes.”
  • In a classroom setting with one infectious individual, two HEPA filters reduce the concentration of airborne virus particles by a factor of 4. Combined interventions (masking, natural ventilation and HEPA filtration) produced a >30 fold reduction
  • Another classroom study of HEPA filtration demonstrated a 90% reduction in aerosol concentration and an estimated 6 fold reduction in inhaled dose with an air change rate of 5-6 per hour.
  • In a conference room setting the combination of the two HEPA air cleaners and universal masking reduced overall exposure to airborne particles by up to 90%. The air cleaners were most effective when they were located in the centre of the room close to the aerosol source. Moreover, the combination of HEPA air cleaners and universal masking was more effective than was either intervention alone.
Portable HEPA filter air purifiers cost in the region of $500, and we urge clinics to consider using them in spaces where potential-Covid patients might be treated.
At least one NZ urgent care clinic is already using HEPA air purifiers, and one Australian ED has them in every patient treatment and waiting area.
Air purifiers are available through mainstream retail stores.
  • Basic models like this feature a HEPA filter (Grade H11) that removes 99.5% of particles as small as 0.3 microns and greater from the air if setup speed and budget are of concern.
  • The ED mentioned above uses Beurer and Samsung models.
  • The Melbourne study used .. domestic appliances (Samsung™ AX5500K) equipped with H13 HEPA filters capable of filtering 99.97% of particles at a Clean Air Delivery Rate of 467 m3/hr on the highest fan speed setting.”

Further information

Technical recommendations for HEPA filtration from the Healthy Buildings Program at the Harvard School of Public Health (Highly recommended – note there are three spreadsheet tabs)
How can airborne transmission of COVID-19 indoors be minimised?