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

Red and green streaming patients. Assessment of red stream patients outside the clinic as much as possible. This may include in cars, carparks, portable cabins or separate assessment areas which are isolated from the rest of the clinic.
Universal masking for all patients and staff
Minimise length of stay in the clinic of patients with covid symptoms
Telemedicine and bookings where practicable
Review the adequacy of the ventilation system of your clinic. “Many of the current ventilation strategies that rely on centralised air distribution and ceiling level supply or recirculation can provide the optimum conditions for rapid disease spread in high occupancy buildings”
This will include an assessment of the percentage of fresh vs recirculated air that the HVAC system supplies, and the level of filtration of any recirculated air. ASHRAE recommends MERV13 filters or higher for air recirculated by HVAC systems.
Additional measures should be taken to mitigate risk, particularly where ventilation / filtration by HVAC systems is deemed inadequate for a healthcare setting. These include:

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.

Be aware that there are various levels of quality and that true HEPA filters are preferable to “HEPA like” or similar descriptions.
Avoid “add-ons” like ioniser functions
Ensure that the clean air delivery rate (CADR) of the filter(s) is sufficient for the volume of the room to provide 5-6 air changes per hour (ACH). (The requirement may be up to 9 ACH in high risk settings in a pandemic.)

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 https://www.kmart.co.nz/product/large-family-air-purifier/2998311 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?

https://www.cdc.gov/coronavirus/2019-ncov/community/ventilation.html#refphf