Why climate change appears to be increasing the frequency of food-borne illnesses

Climate change appears to be fuelling a rise in people getting sick from food-borne illnesses in Canada and around the world, says a Canadian food safety expert.

The disparate causes include increased flooding that is washing contaminants like salmonella, Listeria and E. coli onto crops, and rising ocean temperatures that allow bacteria to flourish in shellfish.

"As the planet becomes warmer and the air temperature becomes warmer, I expect that we're going to see more outbreaks," said Lawrence Goodridge, a professor of food safety at the University of Guelph in Ontario.

While precise numbers linking climate change to food-borne illness aren't available, Goodridge has tracked a growing number of examples of the link between the two.

Last year in North Carolina, Hurricane Florence caused widespread flooding.

Floodwaters led to lagoons of hog waste at farms overflowing and contaminating crops, said Goodridge. The contaminants in those floodwaters forced the state to ban crops in flooded areas from being used for human consumption.

Destructive weather events like hurricanes can also cause a spike in food-borne illnesses because of the widespread power outages they often create.

"If we can't refrigerate our food anymore, you know, as the temperature increases in the refrigerator or freezer, the temperature of the food increases and the bacteria grow," said Goodridge.

But climate change also has more subtle ways of harming the food supply. Over the years, small temperature increases in the ocean have been connected to hundreds of people getting sick in British Columbia, said Eleni Galanis, a physician epidemiologist with the British Columbia Centre for Disease Control.

As the sea warms, it's easier for vibrio bacteria to grow and accumulate in greater numbers in shellfish like mussels and oysters. That's led to an increase in the number of people in B.C. getting sick after eating raw or undercooked shellfish.

Vibrio parahaemolyticus, the most common form of the bacteria found in B.C. waters, causes diarrhea in humans that can last for up to a week and lead to dehydration.

Galanis said that in the last three years, stringent restrictions have been put in place in the shellfish industry to curb the number of people getting sick. The industry now tests for vibrio bacteria and monitors water temperatures where the shellfish grow.

If a shellfish has vibrio, it is placed in a freshwater tank, and because of how it eats food, the bacteria get cleaned out of the shellfish, which then becomes safe to eat.

If a shellfish company notices the top layers of water where the aquatic animals grow are too warm, they would lower the shellfish into deeper, cooler waters to impede bacterial growth.

"I think that's a message of hope that we can counter some of the impacts of climate change in our food sources," said Galanis.

Still, there are lots of hurdles to countering climate change's effect on food-borne illness.

Goodridge said some studies indicate the warming weather will lead to an increase in houseflies.

"They fly onto manure or feces, and then they come and fly onto food, so they can deposit those pathogens on food," he said.

Despite concerns about food-borne illnesses increasing because of climate change, little research is being conducted to determine how many people are actually being made sick, said Goodridge.

He said while Canada has some of the best methods for monitoring food safety in the world, few systems are in place to track how food-borne illness is connected to climate change.

Goodridge said we live in a reactive society, so fears we'll only act once a huge outbreak linked to climate change makes large numbers of people sick and leads to deaths.

"I think if history tells us anything, that is the wrong approach," he said.

To change that, Goodridge and others have been researching ways to safely kill bacteria on fruits and vegetables.

He said bacteria can be destroyed if food is cooked thoroughly, but most fruits and vegetables are consumed raw, and washing them won't necessarily remove harmful bacteria.

Researchers have turned to plants that contain naturally occurring chemicals that kill bacteria. Those chemicals can be extracted and turned into an antimicrobial spray that can be applied to fruits and vegetables.

There are also bacteriophages — naturally occurring viruses that infect and kill bacteria — that are increasingly being used to kill off bacteria. Each phage infects specific bacteria and won't harm others, such as healthy gut bacteria that help people digest food, said Goodridge.

He says roughly one in eight Canadians gets sick each year due to a food-borne illness, according to the Canadian Food Inspection Agency. 

"Even though we have a safe food supply, there's still much work to be done," said Goodridge. "As we increasingly see more [extreme] weather events due to climate change, there will be even more work to do."

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