It doesn’t take long for airborne coronavirus particles to make their way through a room. At first, only people sitting near an infected speaker are at high risk, but as the meeting or class goes on, the tiny aerosols can spread.
That doesn’t mean everyone faces the same level of risk, however.
As an engineer, I have been conducting experiments tracking how aerosols move, including those in the size range that can carry viruses.
What I’ve found is important to understand as more people return to universities, offices and restaurants and more meetings move indoors as temperatures fall. It points to the highest-risk areas in rooms and why proper ventilation is crucial.
University campuses have also been struggling with COVID-19. Cases among 18- to 22-year-olds more than doubled in the Midwest and Northeast after schools reopened in August.
As the case numbers rise, the risk to anyone who spends time in those rooms rises as well.
An experiment shows who’s at greatest risk
Most current models describing the role of ventilation on the fate of airborne microbes in a room assume the air is well mixed, with the particle concentration uniform throughout.
In a poorly ventilated room or small space, that is likely true. In those scenarios, the entire room is a high-risk region.
However, in larger spaces, such as classrooms, good ventilation reduces risk, but likely not uniformly. My research shows that how high the level of risk gets depends a lot on ventilation.
To understand how the coronavirus can spread, we injected aerosol particles similar in size to those from humans into a room and then monitored them with sensors.
We used a 30-foot by 26-foot university classroom designed to accommodate 30 students that had a ventilation system that met the recommended standards.
When we released particles at the front of the classroom, they reached all the way to the back of the room within 10 to 15 minutes.
However, because of active ventilation in the room, the concentrations at the back, about 20 feet (6.1 metres) from the source, were about one-tenth of the concentrations close to the source.
That suggests that with appropriate ventilation, the highest risk for getting COVID-19 could be limited to a small number of people near the infected speaker.
As the time spent indoors with an infected speaker increases, however, risk extends to the entire room, even if ventilation is good.
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CDC finally acknowledges the aerosol risk
In the past, the transmission of respiratory diseases has focused on the role of larger particles that are generated when we sneeze and cough.
These droplets fall quickly to the ground, and social distancing and mask wearing can largely prevent infection from them.
The Centers for Disease Control and Prevention finally acknowledged that risk on October 5 after Trump was hospitalized and several other people in or close to the administration tested positive for COVID-19.
While these smaller particles, on average, carry less virus than larger particles that people emit when they cough or sneeze, the high infectivity of SARS-CoV-2 combined with the high viral load before symptoms appear makes these particles important for airborne disease transmission.
How much ventilation is enough?
To minimize COVID-19 transmission indoors, the CDC’s top recommendation is to eliminate the source of infection. Remote learning has effectively done this on many campuses. For face-to-face teaching, engineering measures such as ventilation, partition shields and filtration units can directly remove particles from the air.
Of all the engineering controls, ventilation is probably the most effective tool to minimize infection spread.
Understanding how ventilation lowers your risks of getting COVID-19 starts with air exchange rates. An air exchange of one per hour means that the air supplied to the room over one hour equals the volume of air in the room.
For classrooms, the current regulations of primary air flow correspond to an air exchange of about six per hour. That means that every 10 minutes, the amount of air brought into the room equals that of the volume of the room.
How high the concentration gets depends in part on the number of people in the room, how much they emit and the air exchange rate.
With social distancing reducing classroom populations by half and everyone wearing masks, the air in many indoor spaces is actually cleaner now than it was before the pandemic.
Parts of the room to avoid
It’s important to remember that not all parts of a room are at equal risk.
The corners of the room will likely have a lower air exchange – so particles can linger there longer.
Being close to an air exit vent could mean that airborne particles from the rest of the room could wash over you.
About 95 percent of particles in the room will be removed by a properly functioning ventilation system in 30 minutes, but an infected person in the room means those particles are also continuously emitted.
The pace of particle removal can be accelerated by increasing the air exchange rate or adding other engineering controls such as filtration units. Opening windows will also often increase the effective air exchange rate.
As schools, restaurants, malls and other communal spaces start accommodating more people indoors, understanding the risks and following the CDC’s recommendations can help minimize infection spread.
This story has been updated with the CDC’s newly released guidance on aerosols.
The Canadian government says it will donate up to 200,000 vaccine doses to fight the mpox outbreak in Congo and other African countries.
It says the donated doses of Imvamune will come from Canada’s existing supply and will not affect the country’s preparedness for mpox cases in this country.
Minister of Health Mark Holland says the donation “will help to protect those in the most affected regions of Africa and will help prevent further spread of the virus.”
Dr. Madhukar Pai, Canada research chair in epidemiology and global health, says although the donation is welcome, it is a very small portion of the estimated 10 million vaccine doses needed to control the outbreak.
Vaccine donations from wealthier countries have only recently started arriving in Africa, almost a month after the World Health Organization declared the mpox outbreak a public health emergency of international concern.
A few days after the declaration in August, Global Affairs Canada announced a contribution of $1 million for mpox surveillance, diagnostic tools, research and community awareness in Africa.
On Thursday, the Africa Centres for Disease Control and Prevention said mpox is still on the rise and that testing rates are “insufficient” across the continent.
Jason Kindrachuk, Canada research chair in emerging viruses at the University of Manitoba, said donating vaccines, in addition to supporting surveillance and diagnostic tests, is “massively important.”
But Kindrachuk, who has worked on the ground in Congo during the epidemic, also said that the international response to the mpox outbreak is “better late than never (but) better never late.”
“It would have been fantastic for us globally to not be in this position by having provided doses a much, much longer time prior than when we are,” he said, noting that the outbreak of clade I mpox in Congo started in early 2023.
Clade II mpox, endemic in regions of West Africa, came to the world’s attention even earlier — in 2022 — as that strain of virus spread to other countries, including Canada.
Two doses are recommended for mpox vaccination, so the donation may only benefit 100,000 people, Pai said.
Pai questioned whether Canada is contributing enough, as the federal government hasn’t said what percentage of its mpox vaccine stockpile it is donating.
“Small donations are simply not going to help end this crisis. We need to show greater solidarity and support,” he said in an email.
“That is the biggest lesson from the COVID-19 pandemic — our collective safety is tied with that of other nations.”
This report by The Canadian Press was first published Sept. 13, 2024.
Canadian Press health coverage receives support through a partnership with the Canadian Medical Association. CP is solely responsible for this content.
HALIFAX – The Nova Scotia government says it could be months before it reveals how many people are on the wait-list for a family doctor.
The head of the province’s health authority told reporters Wednesday that the government won’t release updated data until the 160,000 people who were on the wait-list in June are contacted to verify whether they still need primary care.
Karen Oldfield said Nova Scotia Health is working on validating the primary care wait-list data before posting new numbers, and that work may take a matter of months. The most recent public wait-list figures are from June 1, when 160,234 people, or about 16 per cent of the population, were on it.
“It’s going to take time to make 160,000 calls,” Oldfield said. “We are not talking weeks, we are talking months.”
The interim CEO and president of Nova Scotia Health said people on the list are being asked where they live, whether they still need a family doctor, and to give an update on their health.
A spokesperson with the province’s Health Department says the government and its health authority are “working hard” to turn the wait-list registry into a useful tool, adding that the data will be shared once it is validated.
Nova Scotia’s NDP are calling on Premier Tim Houston to immediately release statistics on how many people are looking for a family doctor. On Tuesday, the NDP introduced a bill that would require the health minister to make the number public every month.
“It is unacceptable for the list to be more than three months out of date,” NDP Leader Claudia Chender said Tuesday.
Chender said releasing this data regularly is vital so Nova Scotians can track the government’s progress on its main 2021 campaign promise: fixing health care.
The number of people in need of a family doctor has more than doubled between the 2021 summer election campaign and June 2024. Since September 2021 about 300 doctors have been added to the provincial health system, the Health Department said.
“We’ll know if Tim Houston is keeping his 2021 election promise to fix health care when Nova Scotians are attached to primary care,” Chender said.
This report by The Canadian Press was first published Sept. 11, 2024.
ST. JOHN’S, N.L. – Newfoundland and Labrador‘s chief medical officer is monitoring the rise of whooping cough infections across the province as cases of the highly contagious disease continue to grow across Canada.
Dr. Janice Fitzgerald says that so far this year, the province has recorded 230 confirmed cases of the vaccine-preventable respiratory tract infection, also known as pertussis.
Late last month, Quebec reported more than 11,000 cases during the same time period, while Ontario counted 470 cases, well above the five-year average of 98. In Quebec, the majority of patients are between the ages of 10 and 14.
Meanwhile, New Brunswick has declared a whooping cough outbreak across the province. A total of 141 cases were reported by last month, exceeding the five-year average of 34.
The disease can lead to severe complications among vulnerable populations including infants, who are at the highest risk of suffering from complications like pneumonia and seizures. Symptoms may start with a runny nose, mild fever and cough, then progress to severe coughing accompanied by a distinctive “whooping” sound during inhalation.
“The public, especially pregnant people and those in close contact with infants, are encouraged to be aware of symptoms related to pertussis and to ensure vaccinations are up to date,” Newfoundland and Labrador’s Health Department said in a statement.
Whooping cough can be treated with antibiotics, but vaccination is the most effective way to control the spread of the disease. As a result, the province has expanded immunization efforts this school year. While booster doses are already offered in Grade 9, the vaccine is now being offered to Grade 8 students as well.
Public health officials say whooping cough is a cyclical disease that increases every two to five or six years.
Meanwhile, New Brunswick’s acting chief medical officer of health expects the current case count to get worse before tapering off.
A rise in whooping cough cases has also been reported in the United States and elsewhere. The Pan American Health Organization issued an alert in July encouraging countries to ramp up their surveillance and vaccination coverage.
This report by The Canadian Press was first published Sept. 10, 2024.
