Unpasteurized milk and cheeses made from it are responsible for nearly all foodborne illnesses caused by contaminated dairy products. And the growing popularity of and access to these products threaten to increase the number of disease outbreaks caused by these food items, a new study says.

Unpasteurized dairy products cause 840 times more illnesses and 45 times more hospitalizations than pasteurized products do, according to the article, which will be published in the June issue of the journal Emerging Infectious Diseases.

“Consumer demand for organic and natural foods … has been on the rise. However, in contrast to some perceptions, natural food products are not necessarily safer than conventional ones, as evidenced by higher rates of foodborne illnesses associated with unpasteurized dairy products,” wrote the authors, consultants for EpiX Analytics of Boulder, Colo.

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There are roughly 760 reported cases of foodborne illness caused by unpasteurized milk and raw milk cheeses a year and on average 22 of those people require hospitalization, the study said.

Those figures are likely the tip of a much larger iceberg, said Kirk Smith, who is supervisor of the foodborne, waterborne, vectorborne, and zoonotic sector of the Minnesota Department of Health. Smith said the database from which the figures were drawn captures outbreaks. Individual cases of illness typically don’t come to the attention of these kinds of detection systems.

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“Outbreaks get all the press. But really the non-outbreak associated cases probably really dwarf the number of outbreak-associated cases,” said Smith, who was not involved in this study.

Unpasteurized or raw milk and raw milk cheeses can be contaminated with a number of different bacteria that can make people sick, including E. coli, salmonella, listeria, and Campylobacter. These bacteria can trigger vomiting and diarrhea, but can cause more severe illnesses as well.

Campylobacter infection can lead to Guillain-Barré syndrome, a form of progressive paralysis from which most but not all people recover. Some strains of E. coli can cause hemolytic uremic syndrome, which can lead to kidney failure. Listeria infections in pregnancy can result in miscarriage, and people with severe listeria infections can die.

“Raw milk is a risky product and is linked to a lot of outbreaks,” said Megin Nichols, who works on raw milk related issues in the Centers for Disease Control and Prevention’s division of foodborne, waterborne, and environmental diseases. “Especially states that allow the legal sale of raw milk for human consumption, those states have more raw milk related outbreaks of illnesses than states that do not allow the sale of raw milk legally.”

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The Food and Drug Administration prohibits distribution of raw milk across state lines if it has been packaged for sale to the public. Raw milk can only cross state lines if it is en route to a pasteurization facility or is slated to be made into aged cheese.

Raw milk regulations, state by state The Food and Drug Administration does not permit the sale of raw (unpasteurized) milk for human consumption, and advises states not to allow the sale of raw milk. But rules regarding raw milk regulation within a state are set by the individual jurisdiction. Some states permit the sale of raw milk in retail stores, some at farmers markets, etc., some on a farm, some permit cow-share programs, and some states only allow the sale of raw goat milk. All other states ban the sale of raw milk for human consumption. Talia Bronshtein Source: National Conference of State Legislatures

It has been thought that cheese made from raw milk was safe to eat if it is aged for 60 days; the aging is thought to kill harmful bacteria. But the FDA is currently reviewing the scientific basis for that position.

Rules regarding raw milk regulation within a state are set by the individual jurisdiction. And those rules are a mishmash.

Although 19 states prohibit raw milk sales, 31 have regulations that allow consumers access to raw milk. Some states allow sales of raw milk in stores, others restrict those sales to farmers markets or on the farm. Some states allow consumers to buy a share of a cow or a herd, which would give them access to raw milk. A couple of states restrict raw milk sales to goat’s milk.

Though public health experts have long warned against drinking raw milk and eating cheeses made with unpasteurized milk, the consumption trend seems to be going in the opposite direction. “We are seeing the trend towards more permissive sale of raw milk,” Nichols said.

The locavore movement — favoring foods produced locally — as well as the growth of artisanal cheese production may be contributing to this. Nichols noted that consumers need to know that just because a product is labeled “organic” or “local” doesn’t mean it is safe to consume — and that’s especially true with dairy products.

Pasteurization is a process for preventing spoilage that dates back to 1864 when French scientist Louis Pasteur discovered that heating wine to just below the boiling point kept it from going sour. The process has been used in milk production for decades.

Before it was adopted, illnesses caused by milk consumption were common — a fact that appears to have been lost with the passage of time, Smith said. “I think people just kind of forget how things used to be before we had these public health advances.”