Raw milk could be riskier amid avian flu outbreak in U.S. Stick to pasteurized dairy, experts warn

An outbreak of avian flu in U.S. dairy cattle has federal officials in Canada and the U.S. testing milk sold in stores to ensure pasteurization and other food safety measures are working. 

Cows sickened with H5N1 in the U.S. produced milk that was abnormally thick and yellowish. The first known outbreak of this form of H5N1 in dairy cattle has since been confirmed in several U.S. states.

After U.S. scientists discovered fragments of the virus in one in five samples of processed milk, officials on both sides of the border introduced surveillance of milk being sold on store shelves to ensure it is free of traces of the virus.

Early research from the U.S. Food and Drug Administration shows pasteurization works to neutralize H5N1, even when fragments of the virus are present in milk.

No cases have been reported in Canadian cows. The Canadian Food Inspection Agency says commercially sold milk and milk products remain safe to consume, largely because all milk sold and used in most types of cheese in Canada is pasteurized.

Here are some of the measures taken to keep disease-causing bacteria and viruses like bird flu out of dairy products in Canada.

Pasteurization is the process of heating a food to kill germs like bacteria, viruses and moulds. 

"Apart from sanitation and hand washing, milk pasteurization has been the best and most effective food safety intervention in history," said Keith Warriner, a professor of food safety at the University of Guelph's food science department. 

Warriner said dairy products are pasteurized at 72 C for 15 seconds. Historically, that temperature and time were used to reduce a heat-resistant bacterial pathogen in milk called Coxiella burnetii, which causes Q fever, a flu-like illness.

Nowadays, it is pathogens like E. coli O157:H7 in dairy products that lead to outbreaks. But Warriner said such outbreaks are less common in Canada than in the U.S., where some states allow raw milk to be sold.

In Australia, a young boy died in 2014 after his parents gave him unpasteurized (raw) milk to drink, believing it would be good for him. The boy developed haemolytic uraemic syndrome, a complication from bacteria like E. coli getting into the bloodstream and kidneys. 

Warriner pointed to the Australian case to show why Canada continues to mandate pasteurization. 

After milk from several farms is collected and brought to a dairy plant, scientists conduct analytical tests for safety and quality and food processors then skim the cream and pasteurize the products. 

In Canada, farmers may drink raw milk from their own cows but aren't allowed to sell it to others. There have been legal challenges to the mandate.