“Small but detectable amounts” of infectious material H5N1 avian flu A new study co-authored by scientists at the National Institutes of Health found that the virus was able to survive common methods of pasteurizing milk.
According to the survey results, Published The study, published Friday in the New England Journal of Medicine, was based on experiments carried out at the agency’s laboratories, and researchers noted that it differs from findings of infectious H5N1 virus in milk sold in grocery stores.
So far, authorities have not detected the infectious virus in milk samples from supermarkets.
The discovery comes as authorities are still identifying the bodies. New infection cluster An unprecedented outbreak of H5N1 avian influenza in dairy cows this year.
Infections have been detected in cattle on farms in at least 12 states, with most of the cattle that have tested positive. Raw milk The samples were tested for high levels of the virus. Suppressing the sale of raw milk It can spread the virus, Consumers were warned not to drink raw milk..
“This study reflects experimental conditions and should not be used to draw conclusions about the safety of the U.S. milk supply,” a Food and Drug Administration spokesman said in a statement.
In the real world of commercial dairy processing, milk from infected cows would likely be mixed with milk from healthy cows, diluting the virus and making it less likely that it would be present in sufficient quantities to survive. The technical details of pasteurizing milk, as well as additional steps to process the milk, also reduce the risk. Pasteurization involves treating milk with high temperatures for a period of time to kill contaminants.
FDA research findings to date 297 Samples Previous tests have not found any infectious virus in commercially available dairy products, such as milk or yogurt. Harmless remaining fragments of the virus From pasteurization.
Laboratory conditions
“These are more or less laboratory conditions. We think that mechanical pasteurization in dairies is probably more effective than what we have,” said Vincent Munster, chief of the virus ecology division at the National Institute of Allergy and Infectious Diseases.
Munster’s Montana lab has for years studied viruses’ ability to remain infectious under different conditions, including pasteurizing pathogens that were introduced into milk during coronavirus outbreaks. Jordan Camels.
The study looked at two different pasteurization methods and tested them on milk spiked with H5N1 concentrations similar to those found in highly infected cows.
One of the pasteurization methods they looked at involves heating milk to 72°C (about 161°F) for 15 seconds. “High temperature for a short time” The method is widely used in the dairy industry, and milk produced this way still contained “traces of infectious virus,” Munster said.
“We’re really talking about 10 or so virus particles, but the first dose will be somewhere around 10 million or 100 million virus particles,” Munster said.
He also noted discrepancies between lab studies that suggest commercial milk pasteurization is a step ahead against the virus and actual industry practice.
“Pasteurization of dairy products involves an initial step in which milk is raised from 4 degrees to 72 degrees. [Celsius]”And apparently once the temperature reaches about 56 degrees, the virus starts to become inactive,” he said.
The second pasteurization method (63 degrees for 30 minutes) was more effective: within minutes, long before pasteurization was over, infectious virus was no longer detectable.
“Pasteurization was developed to reduce the amount of viable bacteria in milk, so to speak, to extend its shelf life in the refrigerator, and it wasn’t necessarily designed in the first place to inactivate viruses,” Munster says.
Pasteurizing milk for longer or at higher temperatures
Munster believes that simply increasing pasteurization times by five to 10 seconds could give the dairy industry a “safety buffer” that would ensure no active virus remains in the milk, even if the raw milk supply had higher concentrations of infectious virus than in the lab.
“If you want to be 100% sure there’s no active virus, just increasing the pasteurization time by about five to 10 seconds can actually increase your margin of safety,” Munster said.
But an FDA spokesman said testing data to date shows that pasteurization processes used by U.S. dairy companies are effective at killing the H5N1 virus. Many companies “use higher, often much higher, temperatures than the minimum standards and use equipment that heats milk more consistently,” the spokesman said.
“[T]”The United States would be hesitant to change pasteurization standards without data demonstrating a public health need,” the spokesman said, warning that any changes to standards would affect the flavor of dairy products.
The agency has not yet released the results of its own study examining the effectiveness of pasteurizing raw milk against H5N1, which it first announced earlier this year. Quote The “totality of evidence” repeatedly asserts that “commercial milk is safe”
A spokesman said the FDA study is a “top priority for the agency” and they are working to release results in the near future. The agency aims to examine “real-world processing conditions” using equipment used in commercial facilities.
“Sound science is important when making public health decisions like FDA’s regarding food safety, and we take the current situation and the safety of our milk supply very seriously,” the spokesperson said.
Munster said several groups have found that heating milk often completely inactivates the H5N1 virus threat, and the FDA and U.S. Department of Agriculture are also conducting research on pasteurization.
“Fortunately, these pasteurization methods inactivate the virus very well. But I think the focus is two-fold: making sure pasteurization can do the job that we want it to do, and the data shows that it can, and then minimizing the amount of H5N1-positive milk that actually goes into these dairy pasteurization methods,” he said.