NEW YORK (Reuters Health) - Despite significant improvements in animal hygiene over the past several decades, unpasteurized milk can still be contaminated with germs that make people sick, researchers warn in a report in the journal Food Safety.

In recent years, raw milk advocates have claimed that pasteurizing milk destroys beneficial organisms, and that unpasteurized milk is safe and can actually prevent and treat heart disease, cancer and other illnesses, explain Dr. Jeffrey T. LeJeune and Paivi J. Rajala-Schultz of the Ohio State University College of Veterinary Medicine in Columbus.

But in fact, there's some evidence that disease from raw milk may be on the rise, according to the researchers. From 1973 to 1992, there were an average of 2.4 such outbreaks annually, they note, while from 1993 to 2006 there were 5.2 per year.

"Although some of this increase may be a result of increased detection and reporting, it is clear that disease associated with the consumption of raw milk is still an important public health concern in the United States," they state.

Pasteurization involves heating milk to destroy disease-causing organisms, and is "the cornerstone of milk safety," the researchers note. What's more, they add, there's no evidence that this process affects the nutritional content of milk.

Cattle-borne diseases, such as brucellosis and bovine tuberculosis, have been virtually eradicated from US cattle, the researchers note. Nevertheless, cows can harbor bugs that are harmful to humans such as E. coli, Salmonella and Listeria without being sick themselves, and the nutrients contained in milk and its neutral pH make it an excellent bacterial breeding ground, LeJeune and Rajala-Schultz explain. While chilling milk can help keep growth of bacteria under control, it can still leave populations of pathogens large enough to make people ill.

Twenty-six states have banned the sale of raw milk, the researchers note, but "various schemes have been developed to make raw milk available to the consumer," for example selling it as pet food and offering consumers "shares" in cows in return for a supply of raw milk from the animal.

There's no evidence that raw milk has any health benefits, and it can be harmful, LeJeune and Rajala-Schultz warn, particularly for vulnerable groups such as very young people, ill people, older people and people with impaired immune system function. Even healthy young adults can get sick from drinking raw milk, they add.

They conclude: "Physicians, veterinarians and dairy farmers who promote, or even condone, the human consumption of unpasteurized milk and dairy products may be at risk of subsequent legal action."

SOURCE: Food Safety, January 1, 2009.

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