The US Centers for Disease Control and Prevention (CDC) has had to issue yet another warning against drinking raw milk last week.

The reason – 19 states are now on high alert for the Brucella strain RB51, a potentially deadly bacteria linked to unpasteurized dairy. The strain is resistant to first-line drugs and its similarity (symptom-wise) to the common cold or flu can make it hard to diagnose.

This particular outbreak is connected to raw milk produced and distributed from Miller’s Biodiversity Farm in Quarryville, Pennsylvania. Fortunately, only one person has been formally diagnosed with brucellosis but officials have warned that raw milk drinkers across at least 19 states, including Minnesota, Mississippi, and Calfornia, may be affected.

The warning follows an investigation into raw milk sold by Miller’s Biodiversity Farm, which began after a New York resident contracted brucellosis in November 2018. RB51 was detected in milk samples from the farm and a cow that tested positive for the strain has since been separated from the milking herd. 

Anyone who has consumed raw milk (or raw milk products) from the farm since 2016 may have been exposed and should speak to a medical professional, the CDC advises. They also recommend disposing of any products that have been leftover or stored. 

So, what exactly is the deal with raw milk and Brucella? 

Raw milk has become a trend among the health-conscious, organic tribe, considered more "natural" or "real" than pasteurized (heat-treated) alternatives. According to raw milk advocates, it contains more nutrients, probiotics, and flavor than the standard bottle of milk you might buy from a supermarket shelf. Some even go so far as to claim pasteurized milk has been linked to allergies, osteoporosis, arthritis, heart disease, growth problems, and cancer.

But according to the US Food and Drug Administration (FDA), pasteurization does not reduce milk's nutritional value nor does it cause lactose intolerance and allergies. (If you are naturally sensitive to milk proteins, milk will affect you whatever form it comes in.) Or, as one 2015 review on the pros and cons of raw milk puts it: "There is no evidence that raw milk has any inherent health or nutritional benefits, those media claims were shown to be myths."

There are, however, dangers. Milk is heat-treated for a reason. It kills a variety of nasty and life-threatening pathogens, including Salmonella, E. coli, Listeria, and Campylobacter. It also destroys organisms responsible for diseases like typhoid fever, tuberculosis, diphtheria, Q fever – and brucellosis. There is, in sum, a reason it has been adopted by mainstream producers since being developed by Louis Pasteur in 1864.

But now, thanks to the trend for raw milk, cases of preventable diseases like listeriosis and food poisoning are increasing.

According to the CDC, unpasteurized (or raw) milk and cheese is consumed by just 3.2 percent and 1.6 percent of the population respectively. Yet, they are responsible for 96 percent of illnesses caused by contaminated dairy products. That is 849 times more illness and 45 times more hospitalizations than dairy that has gone through the recommended pasteurization process. 

RB51 is actually a weakened strain that is transmitted to cows via a vaccine to protect animals against stronger strains of the bacteria. It can, however, pass into a cow's milk and, therefore, to humans, causing brucellosis.

Once exposed, symptoms may start anytime between five days to six months later and resemble the flu. Think: sweats, loss of appetite, headache, fatigue, muscle, and joint pain. If left untreated, it can develop into something more serious, including arthritis, heart problems, enlargement of the spleen or liver, and even meningitis. 

Because of this, the CDC is advising consumers to "look for the word 'pasteurized' on product labels."