Something in the air
Covid-19 spreads via contaminated surfaces or through airborne transmission, but can the virus move through a hotel’s ventilation system? Brittney Deguara reports.
If a person with Covid-19 is safely tucked away in a hotel room in a managed isolation and quarantine (MIQ) facility, they can’t spread the virus, right?
Maybe. Maybe not.
If this person coughs, sneezes or even breathes near the room’s ventilation system, there appears to be a chance – depending on the type of ventilation installed – that microscopic Covid-19 particles could be sucked up into air ducts and transported through the building, potentially into other parts of the hotel.
This may be the case in the Northland community Covid-19 case discovered on Sunday.
The Ministry of Health is exploring the possibility of infection through ventilation systems in MIQ. It has also suggested replacing filters in some facilities.
Australian scientists are also scrambling to determine whether this is a viable source of transmission after a cluster of cases was detected in a Brisbane MIQ facility. There appears to have been no close contact between the guests.
So what do we know about spread through ventilation? How big is the risk?
How Covid-19 spreads
The two main ways Covid-19 spreads are:
■ An individual inhales large infected droplets expelled by an infected person through, say, coughs or sneezes.
■ An individual touches a contaminated surface covered in viral particles and transfers the virus into their system.
It appears the virus can survive on some surfaces for up to 72 hours. The amount of time it survives depends on the temperature, humidity and UV light.
If someone infected with
Covid-19 coughs near a ventilation system in a building that recirculates air, the infected microdroplets could be redistributed throughout the building.
There is a third way. Covid-19 can be passed on through microdroplets – also known as aerosols – which are also released through coughs and sneezes. While similar to the first form of transmission, epidemiologists see this as a different method, as the virus particles are airborne for much longer.
Gravity normally brings the larger droplets down to earth. But the microdroplets are so small (1 micrometre – which is a length equal to 0.001mm – to 100 micrometres in diameter) that they tend to hover in the air.
They can survive for hours (researchers don’t yet know exactly how long), and how they move depends on what’s going on nearby.
They could be pushed upwards by a person’s body heat, or they could be sucked into a building’s ventilation system. Typically, there are thousands, or hundreds of thousands, of microdroplets expelled when someone sneezes, according to aerosol chemist Dr Joel Rindelaub, from the University of Auckland.
And the bad news is that they can travel tens of metres from where they originated.
This type of transmission is thought to be how two health workers in a Christchurch MIQ facility were infected.
More than 200 experts warned the World Health Organisation (WHO) of the potential for the virus to be airborne back in July.
How ventilation systems work
There are 32 managed isolation and quarantine facilities around the country. The ventilation system in each one is different.
‘‘One of the criteria that is used in selecting hotels suitable for managed isolation in the first place is the nature of their ventilation and air circulation systems,’’ director-general of health Dr Ashley Bloomfield said at yesterday’s news conference.
It is not known what type of ventilation system was used in the Pullman Hotel in Auckland, where the Northland woman was infected. The ministry is working with the hotel to understand whether the system played a role in the infection.
Experts interviewed said that, typically, hotels use a combined heating, ventilating and airconditioning (HVAC) system.
So how does a HVAC system work?
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.
Scott Roberts, engineering director of Jacksons Engineering HVAC Solutions, explained it is more common to have a separate ventilation vent so that, even when the airconditioning is turned off, fresh, clean air is still flowing through the room.
So, in one hotel room you’ll have a ventilation vent bringing in fresh air 24 hours a day, an air-conditioning vent distributing cold or hot air when turned on, and a vent taking out stagnant air through separate ducts. The stagnant air is expelled typically through an exit, usually on the roof. The system shouldn’t leak older or stagnant air into other hotel rooms.
There is another type of ventilation system that recirculates the air.
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 fairly regular filter, not one designed to capture minute particles.
This energy-saving option is common in office buildings. It is also sometimes used in hotel lobbies or restaurants, and hotels in repurposed buildings, according to Roberts.
The WHO advises against this type of ventilation system, due to the risk of infection.
All of these systems are called mechanical systems. Manual or
natural systems – simply opening a window – are also used in most MIQ facilities.
What happens when microdroplets enter ventilation systems?
Once infected microdroplets escape the body, they go on a journey.
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.
Professor David Murdoch, dean of the University of Otago and co-leader of The Infection Group, says more fresh air moving into a room reduces the risk of infection.
So, simply opening a window can reduce the risk of airborne spread, as the microdroplets will be sucked out of the window and dispersed.
With non-circulating HVAC
systems, there appears to be no risk of infected particles moving from room to room through the ventilation system.
A risk still remains, however, for those cleaning and servicing ventilation grates and fans. A Nebraska-based study found a number of grates in rooms with infected patients had traces of the virus.
According to Rindelaub, aerosols on ducts, grates or fans don’t have a long life – they might survive for about
three days.
Are the new variants a problem?
There are still so many unknowns with the South African and UK variants. Preliminary findings show them to be up to 70 per cent more transmissible than earlier variants.
Microdroplets infected with either of these two variants will move through the air the same way earlier variants do, according to Rindelaub.
The new variants share the N501Y mutation in the spike protein – the part of the virus that protrudes from the outside, helping to infect cells. This mutation makes the virus latch on to receptors on cells better than earlier variants.
So, if an MIQ facility has a recirculating ventilation model in place and 1000 microdroplets
travel into another room, it’s possible that these infected particles will have an increased likelihood of latching on to a host than if it were 1000 microdroplets of the earlier variants. But this remains a theory.
How to reduce the risk?
Having a safe ventilation strategy is just as important as wearing PPE, says Rindelaub.
As a way to reduce the risk associated with infection through ventilation systems, a study published in Environment International suggests increasing the amount of outside air coming in and eliminating recirculation.
To eliminate potential exposure to microdroplets on ventilation grates or in ducts, Rindelaub suggests leaving isolation rooms empty for a few days to let the virus degrade. During this time, no cleaners, maintenance staff or new arrivals should enter the room.
The Ministry of Health has started checking the ventilation systems in some MIQ facilities.
Without knowing exactly what ventilation systems are in each facility, it’s hard to gauge the overall risk from this kind of transmission.
We know the virus can move through ventilation systems, so if there are recirculation systems installed, it may well be an issue.