The new national public health warning about the risk of exposure to drug-resistant Brucella from raw milk is over three incidents dating back to 2017, according to the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota.

The federal Centers for Disease Control and Prevention (CDC) in Atlanta issued its latest warning about the antibiotic-resistant Brucella RB51 strain on Jan. 23.

The warning was in response to the third and most recent case involving a New York resident who drank raw milk from Miller’s Biodiversity Farm in Quarryville, PA and who then contracted the RB51 strain.

State health departments in New York and Pennsylvania are currently investigating the Brucella RB51 exposures from the raw milk dairy. It’s possible that Miller’s Biodiversity Farm supplied raw milk to the public in as many as 19 states, according to that CDC Health alert Network (HAN) notice.

Two other recent confirmed cases of Brucella RB51 occurred in July and November of 2017. The victims were both women and residents of Texas and New Jersey.  CDC did not believe those two incidents were related.

The HAN notice CDC issued in 2017 was over raw milk produced under the Udder Milk brand name by unknown dairy farms for distribution in Connecticut, New Jersey, New York, and Rhode Island.

The New York resident learned of the Brucella RB51 diagnosis in November 2018 after drinking raw milk from the Pennslyvania dairy, and milk samples from the farm also tested positive for Brucella RB51. Anyone who drank raw milk or consumed other raw milk products from the dairy since 2016 is at risk of exposure, according to CDC.

Brucella strain RB51 is a live-attenuated cattle vaccine strain, which can be shed in milk and can cause infections in humans who consume milk that is not pasteurized. It is resistant to rifampin and penicillin. CDC recommends both doxycycline and trimethoprim-sulfamethoxazole as first-line treatment. The diagnosis should involve a blood culture.

Among the symptoms of brucellosis are fever, sweats, general malaise, loss of appetite, headache, fatigue, muscle, and joint pain, along with potentially more severe complications like endocarditis and neurologic symptoms. Pregnant women are at risk of miscarriage.

RB51, according to CDC,  is a weakened strain of Brucella abortus bacteria used to vaccinate young female cattle. Intensive vaccination campaigns have nearly eradicated B. abortus, which can cause abortions in cattle. The bovine vaccine reduces the risk of people contracting brucellosis from infected cows. However, in rare cases, vaccinated cows can shed RB51 in their milk. The only way to avoid this potential exposure to RB51 is to drink pasteurized milk. The heat of pasteurization kills RB51, other types of Brucella, and a variety of other disease-causing bacteria.

Human brucellosis cases in the United States have fallen from about 3,000 per year in the 1950s to 100-150 –per year in recent years. Most cases of brucellosis in the U.S. are caused by strains other than B. abortus and occur in people who traveled to countries wher Brucella is more common and drank contaminated milk or had contact with infected animals.

CDC reports that among cases who acquired brucellosis in the U.S., infections occur from contact with feral swine or, more rarely, dogs, or because of accidental exposures among lab workers testing samples from ill people.