Is it cold, COVID or the flu? Experts say its ‘very difficult’ to differentiate

As flu season approaches amid the rise of new COVID-19 variants, experts say it’s very difficult to differentiate between a cold, flu, or a COVID-19 infection and regardless of what an infected person has, Canadians still need to wear masks and physically distance themselves from others in order to stay safe.

“A lot of these illnesses have overlapping symptoms…like a runny nose, sore throat, general aches, fatigue, and cough…these are features of all of them,” Isaac Bogoch, an infectious diseases specialist at the Toronto General Hospital tells Global News.

“It’s going to be very challenging to conclusively separate a cold, influenza, and COVID 19.”

Typically, Canada reaches the beginning of flu season from late October to early January, a Public Health Agency of Canada (PHAC) spokesperson told Global News in May. 

Bogoch says if a person is feeling unwell, they should stay home.

“You don’t want to get anyone else sick…we know how transmissible COVID-19 is and you shouldn’t be going into a workplace or a school to transmit it to others,” said Bogoch.

Earlier this week, Prime Minister Justin Trudeau urged Canadians to get vaccinated againstCOVID-19 and influenzato reduce the “danger” of needing other health measures this winter.

“One of the things to remember as flu season approaches is people got to get vaccinated, whether it’s getting the flu vaccine or getting up-to-date on your COVID shots,” he told reporters on Monday.

The National Advisory Committee on Immunization (NACI) also “strongly” recommends COVID-19 bivalent vaccines to be given as boosters this fall over the original shots, which vaccine makers retooled to better target the ever-changing virus. At the same time, certain pharmacies have opened up their online portals to get Canadians in line for their flu shot when it becomes available in the respective region.

Though there’s no specific way to differentiate between the flu, cold or COVID based on symptoms alone, Bogoch says COVID-19 rapid tests can still be useful, at least in the first five to 10 days of being infected.

“It’s a pretty decent indicator…we don’t want to infect others. It’s something that we can prevent,” said Bogoch, adding that even if a person gets a negative test, they should still take their symptoms seriously.

However, Dr. Earl Rubin, director of the infectious disease division of the Montreal Children’s Hospital, says people need to understand the limitations of a rapid test.

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“A negative rapid test in somebody who has no symptoms is not really that helpful. If your symptoms just started a few hours before, it may take two or three days for the rapid test to become positive,” said Rubin.

He said that about 25 per cent of COVID-19 cases never become positive, but “certainly a positive test is useful.”

“We would want people to still kind of exclude themselves for five days, be careful around vulnerable people and wear a mask,” said Rubin.

He says that currently there are a lot of respiratory viruses going around. One in particular is the respiratory syncytial virus, or RSV.

“It’s very difficult to differentiate, never mind RSV from COVID or any of the respiratory viruses, because with the newer variants, Omicron, in particular, the symptoms are more of an upper respiratory tract infection. So, the runny nose, the sore throat, the blocked nose, the cough, things that everybody prior to COVID is very familiar with in terms of any viral illness,” said Rubin.

He says the only thing that really helps in knowing what you’re infected with is if a known contact has tested positive for COVID. That, in a way, eliminates the possibility of flu or a common cold.

“We will see what time will bring in terms of influenza, which can also give that high fever and (make you) sick for a number of days similar to COVID. Right now, we don’t have that much influenza. Not yet anyway, but we expect it to come. So, it’s very difficult to differentiate,” Rubin said.

He says what also makes it difficult for clinicians to differentiate is the fact that more children are getting sick of late and showing severe symptoms from common viruses like RSV.

During the pandemic, Rubin says, people were wearing masks, distancing, and working from home so children weren’t getting infected by common viruses and as a result they may now be lacking in immunity.

“Thankfully…healthy young children don’t get that sick with COVID, but they can get equally as sick with influenza,” said Rubin. “We’re also seeing that younger children are not immune to (common viruses) because they weren’t getting them in the last two years.”

Dr. Rod Lim, site chief of Children’s Hospital’s pediatric emergency department, previously told Global News it “will be a quite challenging season” with the susceptibility of children getting sick.

“We know that children have basically been sheltered for two to two and a half years now, so the susceptibility of the population is very high, and the mixing is almost back to pre-pandemic levels. So, we do anticipate that this will be quite a challenging season,” he said.

Lim added that respiratory viruses are also not following historic time trends, meaning health-care workers don’t know when influenza will hit and whether it will correspond with other viruses that may be circulating, such as COVID-19, or respiratory syncytial virus, or RSV.

“All of this is making it very difficult clinically just to look at somebody and say, this is COVID or otherwise,” said Rubin.

He said kids should do a COVID test if they can, and if they’re sick and showing symptoms then they should stay home.

“If a COVID test is done and is shown to be negative repeatedly, then kids in school or anybody in the community should be wearing masks,” said Rubin. “(Masks) are really important…that will not only help limit the spread of COVID, but hopefully the other respiratory viruses that are there as well.”

— with files from Matthew Trevithick and Aaron D’Andrea