VAIL, COLO. – Aged cheese made from unpasteurized milk is not pathogen free and has been responsible for numerous food poisoning outbreaks, Dr. Mary P. Glodé said at a conference on pediatric infectious diseases sponsored by the Children’s Hospital Colorado.
A common misperception is that the aging or curing process involved in cheese making kills any pathogens present in raw milk. Not so. Last February the Food and Drug Administration and Health Canada jointly published a draft assessment of the risk of listeriosis from soft-ripened cheese. Listeriosis is the third leading cause of death from food poisoning in the United States. The agencies found that the risk of listeriosis was 50-160 times greater per serving if the cheese was made with raw, unpasteurized milk than with pasteurized milk.
The public comment period regarding the draft document has expired, and the FDA is expected to soon announce some sort of action. Possibilities include adopting a European-style approach featuring much closer regulation of animal health and hygiene during the milk collection process so that milk is less contaminated as it comes from the animal, extending the current 60-day aging rule for cheese to 90 days or longer in order to help eliminate pathogens, or banning all cheeses made with raw milk from interstate commerce. The FDA banned interstate commerce of raw milk in 1987, but made an exception for cheese made from raw milk provided it was aged for at least 60 days, noted Dr. Glodé, professor of pediatrics and section head of pediatric infectious diseases at the Children’s Hospital Colorado and the University of Colorado, Denver.
Despite the 26-year-old ban on interstate transport of fluid raw milk, enthusiasts throughout most of the country are still able to obtain it. Raw milk sales are illegal in only a handful of states. Retail sale is legal in 10 states, and on-the-farm sale is legal in another 16. In other states, it’s possible to acquire a share in a raw milk herd or purchase raw milk as "pet food."
A Centers for Disease Control and Prevention analysis concluded that 85% of a series of 239 hospitalizations due to tainted dairy products involved raw milk or cheese made from raw milk. Almost two-thirds of the hospitalized individuals were under age 20.
The CDC estimates that 1.3 million food-borne illnesses due to contaminated dairy products occur annually in the United States, with half involving pathogenic bacteria. Eighty percent of food-borne illness outbreaks involving fluid milk are due to unpasteurized milk, even though less than 1% of milk consumed in the United States is unpasteurized.
Pathogens detected in up to 5%-11% of samples gathered from bulk tank milk used for raw milk cheese production include Escherichia coli 0157, Salmonella, Shigella, Yersinia enterocolitica, Listeria monocytogenes, and Campylobacter jejuni.
Yet raw milk or cheese made from raw milk is by no means always the culprit in food-borne illnesses due to tainted dairy products. For example, a CDC analysis of all reported cases of listeriosis in 2009-2011 implicated cheese in 6 of 12 outbreaks affecting 38 states – but the culprit cheese was made from pasteurized milk in 5 of the 6 outbreaks. Since the cheese was made from pasteurized milk, it is likely that the contamination occurred later, during the cheese-making process. Mexican-style cheeses made from pasteurized milk were implicated in four outbreaks, a chive and white brine cheese made from pasteurized milk was identified as the source in another, and an aged blue cheese made from raw milk was implicated in one multistate outbreak (MMWR 2013;162:448-52).
Raw milk advocates claim the product is more nutritious than pasteurized milk, but this hasn’t held up under scientific scrutiny, Dr. Glodé said.
A more intriguing argument for raw milk, in her view, comes from a single British cross-sectional study, the Study of Asthma and Allergy in Shropshire, which ended up linking consumption of unpasteurized milk to the hygiene hypothesis of atopy.
This was a large-scale study led by investigators at St. George’s University of London. It aimed to determine the explanation for the often-documented observation that farmers’ children have a reduced prevalence of allergic disorders. The investigators queried the parents of nearly 5,000 rural children regarding the kids’ diet, allergic status, and farming exposures, then performed skin prick and blood testing in 879 of the children.
Children who consumed unpasteurized milk, even infrequently, had a 41% reduction in current eczema symptoms as well as a 76% reduction in atopy compared with non–raw milk drinkers. Total IgE levels were 59% lower in the raw milk drinkers, and they also showed greater production of whole blood stimulated interferon-gamma. These benefits were seen regardless of whether the rural raw milk–drinking children were in farming or nonfarming families.