We know that COVID-19 can spread via contaminated surfaces and through airborne transmission, but what about air-conditioning and ventilation systems?
There appears to be a chance, depending on the type of ventilation installed, that if a person staying in a hotel room in a managed isolation and quarantine (MIQ) facility coughs or sneezes or even breathes near the room’s ventilation system, microscopic COVID-19 particles can be sucked into the air ducts and transported through the building, potentially into other parts of the hotel.
The Ministry of Health is exploring the possibility of infection through ventilation systems in quarantine facilities in the wake of the Northland community case. The Ministry has also suggested replacing filters in some facilities.
How big is the risk of spreading COVID-19 through hotel ventilation?
The two main ways COVID is spread:
- An individual inhales large, infected droplets expelled by an infected person through airborne transmission (such as a cough or a sneeze)
- An individual touches a contaminated surface covered in viral particle and transfers the virus to their system (for example by touching their face)
But COVID-19 can also be passed a third way, through microdroplets (also known as aerosols) – these are also released through talking or coughing. This is similar to the first form of transmission; however, epidemiologists see this as a different method as the virus particles are airborne for much longer.
While gravity normally brings larger droplets down to earth, microdroplets are so small that they tend to hover in the air. The other bad news is that they can travel tens of metres from where they originated.
In July 2020, more than 200 experts warned the World Health Organisation of the potential for the virus to be airborne and it is this type of transmission that is thought to be how two health workers in a Christchurch MIQ facility were infected.
Each ventilation system in each of the 32 MIQ facilities around the country is different. It is not known what type of ventilation system was used in the Pullman Hotel where the Northland woman was infected, the Ministry of Health is working with the hotel to understand if the system played a role in the infection.
“One of the criteria used in selecting hotels suitable for managed isolation in the first place is the nature of their ventilation and air circulation systems," explained Director-General of Health Dr Ashley Bloomfield at Monday’s news conference.
Most hotels use a combined heating, ventilating, and air-conditioning (HVAC) system.
How an HVAC system works:
In hotels, fresh air is usually sucked inside through a fan on the building’s roof. It is then cleaned as it passes through a standard filter. The filters are designed to rid the air of dust and bugs, but not minute particles or COVID-19 microdroplets.
From here, there are two ways fresh air can come into a room:
- Through one vent that channels in conditioned (hot or cold) air and fresh new air.
- Or through two separate vents.
Typically, in one hotel room, there is a ventilation vent bringing in fresh air 24 hours a day, and air-conditioning vent distributing cold or hot air when turned on, and a vent taking out all the old, stagnant air through separate ducts. The stagnant air is usually expelled through an exit on the roof and a system should not leak older or stagnant air into other hotel rooms.
There is another type of ventilation system, however, that recirculates the air. This is an energy-saving option common in office buildings.
Instead of simply removing old air, this type of system cleans the air and redistributes it through the building. The system would typically use a regular filter, not one designed to capture minute particles. The World Health Organisation has advised against this type of ventilation system.
What happens when microdroplets enter a ventilation system?
Once infected microdroplets escape the body they may be sucked up into the air duct and moved through the ventilation system, or, if there’s an open window, they’ll just be sucked outside.
More fresh air moving into a room can reduce the risk of infection, simply opening a window can reduce the spread as microdroplets will be sucked out the window and dispersed. The chances of infection from particles floating outside is significantly less than if they spread within a room and with non-circulating HVAC systems, there appears to be no risk of particles moving from room to room through the ventilation system.
Of course, there are still many unknowns regarding the new variants of the virus from South Africa and the UK. Preliminary findings show them to be up to 70 percent more transmissible than earlier variants.
How to reduce the risk?
According to experts, having a safe ventilation strategy is as important as wearing PPE.
A study published in Environment International has suggested increasing the amount of outside air coming in and eliminating recirculation to reduce the risk associated with infection through ventilation systems.
The Ministry of Health has said it is starting to check the ventilation systems in some MIQ facilities.