RB51 brucellosis in humans has historically been associated with which exposure?

• A. Drinking raw milk
• B. Vaccine needle sticks and exposure to aborted infected calves/placentas
• C. Handling dairy products
• D. Eating undercooked beef

Answer: (B)

RB51 brucellosis in humans is tied to exposure to the vaccine strain itself, not to eating or drinking typical foods. This live attenuated vaccine is used in cattle, and human infections have historically occurred mainly from occupational exposure during vaccination or from contact with aborted infected calves or their placentas. Needle-stick injuries or direct contact with birth fluids and tissues can introduce the vaccine strain into a person, leading to brucellosis. While brucellosis can be acquired from unpasteurized dairy or certain animal products, those routes are not the classic exposure story for RB51 specifically, making vaccine handling and aborted-tissue exposure the best-fitting association.