Infectious bird flu survived milk pasteurization in lab tests, study finds. Here’s what to know.

A “small but detectable amount” of infectious diseases H5N1 bird flu The virus was able to survive a common approach to pasteurizing milk, according to new research co-authored by scientists at the National Institutes of Health.

The evidence, Published Friday in The New England Journal of Medicine, were based on experiments carried out in the agency’s laboratory. The researchers note that this is not the same as finding the infectious H5N1 virus in supermarket milk.

So far, authorities have not detected infectious viruses in any supermarket milk samples.

The discovery comes while authorities are still identifying new infected herds in this year’s unprecedented outbreak of H5N1 avian influenza in dairy cattle.

Infections have been detected in cows on farms in at least a dozen states, with the majority of positive tests coming from raw milk samples that were full of viruses. The authorities called on States to restrict raw milk sales that could spread the virus and have warned consumers against consuming raw milk.

“The study reflected experimental conditions and should not be used to draw any conclusions about the safety of the U.S. milk supply,” a Food and Drug Administration spokesperson said in a statement.

In the real world of commercial dairy processing, milk from infected cows is likely being mixed with milk from healthy cows, diluting the virus and making it less likely there will be enough of it to survive. Technical details of how milk is pasteurized, as well as additional steps to treat it, also reduce risk. Pasteurization involves treating milk at high temperatures for a period of time to eliminate contamination.

Results from previous FDA studies on 297 samples of retail dairy products, such as milk and yogurt, did not detect any infectious viruses. Previous tests found only a few harmless fragments of virus remains from pasteurization.

Laboratory experimental conditions

“These are more or less experimental laboratory conditions. And we think that mechanical pasteurization in dairy production will probably be more effective than what we do,” said Vincent Munster, head of the virus ecology unit at the National Institute of Allergy and Infectious Diseases.

Munster’s laboratory in Montana has been working for years studying the ability of viruses to remain infectious under a variety of conditions, including previous work on pasteurizing pathogens in milk, such as a coronavirus outbreak in Jordanian camels.

In this study, they looked at two pasteurization approaches, tested on milk with added H5N1 concentrations at levels similar to those seen in some highly infectious cows.

One pasteurization method analyzed milk heated to 72 degrees Celsius (about 161 degrees Fahrenheit) for 15 seconds, similar to “high temperature for a short time” method that is widely used throughout the dairy industry. This yielded milk that Munster said still contained “minimal amounts of infectious virus.”

“We’re really talking about about 10 virus particles, whereas the initial dose would be somewhere around 10 million or 100 million virus particles,” Munster said.

He also pointed out differences between the laboratory study and real-world industrial practices that give commercial milk pasteurization a head start against the virus.

“There is an initial period in the pasteurization of dairy milk where the milk needs to go from, say, 4 degrees to 72 degrees. [Celsius]. And obviously, when it starts to reach about 56 degrees, it starts to inactivate the virus,” he said.

The second pasteurization approach – half an hour at 63 degrees Celsius – was more effective. The infectious virus was undetectable within 20 seconds, long before pasteurization was complete.

“Pasteurization methods were developed to actually reduce the amount of viable bacteria in milk to extend the shelf life of the refrigerator, so to speak. And they are not necessarily designed initially to inactivate viruses,” Munster said.

Pasteurize milk for longer or at higher temperatures

Munster believes that even adding an additional 5 to 10 seconds of pasteurization could offer the dairy industry a “safety buffer” by ensuring that there are no remaining active viruses in the milk, even if its raw milk supply has higher concentrations of infectious viruses than than the laboratory. .

“If you really want to be 100% certain that there is no active virus, increasing the pasteurization duration by as much as 5 to 10 seconds would allow you to increase that safety margin,” Munster said.

But an FDA spokesperson said testing data so far shows that the pasteurization processes used by U.S. dairy companies are effective in killing H5N1. Many companies “use higher temperatures, often much higher than minimum standards,” the spokesperson said, and equipment that heats milk more consistently.

“[T]The United States would be hesitant to change pasteurization parameters without data demonstrating a public health need,” the spokesperson said, warning that changing standards would affect the taste of dairy products.

The agency has so far not released the results of its own study to validate raw milk pasteurization for H5N1, first announced earlier this year. Last month, it was cited “the totality of the evidence” by reiterating that “the commercial supply of milk is safe”.

The spokesperson said the FDA study “is a top priority for the agency” and that they are working to share the results in the near future. The agency seeks to validate “real-world processing conditions” with equipment used in commercial facilities.

“Sound science is critical to informing public health decisions, like those made by the FDA, related to food safety, and we take the current situation and the safety of the milk supply very seriously,” the spokesperson said.

Munster said the FDA and the U.S. Department of Agriculture also have studies on pasteurization among several groups that have confirmed that heating milk is often able to completely inactivate the threat of the H5N1 virus.

“Fortunately, they inactivate viruses very well. But I think the point of focus should be twofold: ensuring that pasteurization is up to the task that we’re asking it to do, and the data suggests that it is, but also that we should minimize any virus-positive milk.” H5N1 to actually enter dairy pasteurization,” he said.