One person was sickened and an unknown number of people in 19 states were exposed to potentially serious bacteria after consuming unpasteurized milk from a Lancaster County farm.

The Centers for Disease Control and Prevention issued a food safety alert Friday after milk samples from Miller’s Biodiversity Farm in Quarryville tested positive for Brucella strain RB51. A New York resident who drank unpasteurized milk purchased from the farm was diagnosed with brucellosis in November 2018, according to the CDC.

Pasteurized dairy products were not affected. Heating milk to a specific temperature for a certain period of time, a process pioneered by Louis Pasteur in 1864, kills not only Brucella but also organisms causing listeriosis, typhoid fever, tuberculosis, diphtheria, and other illnesses, according to the U.S. Food and Drug Administration. Devotees of raw milk products assert that pasteurization degrades dairy’s nutritional value and shelf life, and makes people more likely to have lactose intolerance, all of which the FDA calls myths.

Miller’s Biodiversity Farm referred a call for comment to the Real Food Consumer Coalition, which acts as a consultant for the farm.

The cow that tested positive for RB51 has been removed from the milking herd, according to the CDC.

The animal, which was purchased along with others from a facility in Virginia, was vaccinated with the RB51 strain of the vaccine, according to Liz Reitzig of the Real Food Consumer Coalition. The vaccine usually protects about 70 percent to 80 percent of the vaccinated animals from average exposure, according to the U.S. Department of Agriculture.

In December 2018, the state Department of Agriculture issued an order for Miller’s Biodiversity Farm to stop sales of any dairy products made with raw cow’s milk while the investigation was conducted.

The CDC warned that anyone who consumed raw milk or raw milk products from this dairy farm since January 2016 might have been exposed. It urged people who consumed the products to contact a doctor to determine if they are infected and to avoid long-term health problems caused by brucellosis.

Brucellosis is an infectious disease found in sheep, cattle, goats, pigs, dogs, and other animals and can spread to humans who come in contact with infected animals or animal products contaminated with the bacteria. Person-to-person spread of the bacteria is rare, according to the CDC.

Early cases of brucellosis are difficult to diagnose because the symptoms, which can include fever, sweats, loss of appetite, headache, fatigue, muscle and joint pain, are similar to flu. The infection can lead pregnant women to miscarry. If left untreated, complications such as arthritis, heart problems, enlargement of the spleen or liver, and meningitis can develop. Symptoms can start anywhere from five days to six months after exposure.

The RB51 strain is resistant to first-line antibiotics.

In September 2017, a New Jersey woman became ill from Brucella RB51 after drinking unpasteurized milk from the New York-based company Udder Milk.