How did 6,000 people in China get infected by brucellosis in single outbreak?

More than 6,000 people in China have been infected by brucellosis in a single outbreak that originated at a biopharmaceutical factory last year. The factory had used expired disinfectants to make brucellosis vaccines, leaving the bacteria in its waste gas. The contaminated gas later formed aerosols that drifted downwind to a veterinary institute in Lanzhou, infecting students there.