Bacterial outbreak infects thousands after factory leak in China

A microscope view of the brucella bacterium responsible for brucellosis, also known as Malta fever.

(CNN)Several thousand people in northwest China have tested positive for a bacterial disease, authorities said on Tuesday, in an outbreak caused by a leak at a biopharmaceutical company last year.

The Health Commission of Lanzhou, the capital city of Gansu province, confirmed that 3,245 people had contracted the disease brucellosis, which is often caused by contact with livestock carrying the bacteria brucella.
Another 1,401 people have tested as preliminarily positive, though there have been no fatalities reported, the city's Health Commission said. In total, authorities have tested 21,847 people out of the city's 2.9 million population.
    The disease, also known as Malta fever or Mediterranean fever, can cause symptoms including headaches, muscle pain, fever and fatigue. While these may subside, some symptoms can become chronic or never go away, like arthritis or swelling in certain organs, according to the United States' Centers for Disease Control and Prevention (CDC).
      Human-to-human transmission is extremely rare, according to the CDC. Instead, most people are infected by eating contaminated food or breathing in the bacteria -- which seems to be the case in Lanzhou.
      This outbreak stemmed from a leak at the Zhongmu Lanzhou biological pharmaceutical factory, which occurred between late July to late August last year, according to the city's Health Commission. While producing Brucella vaccines for animal use, the factory used expired disinfectants and sanitizers -- meaning not all bacteria were eradicated in the waste gas.
      This contaminated waste gas formed aerosols that contained the bacteria -- and leaked into the air, carried by wind down to the Lanzhou Veterinary Research Institute, where the