At least 3 200 people in the northwestern province of Gansu, China, have tested positive for a bacterial zoonotic disease called Brucellosis, authorities said this week, in an outbreak caused by a leak at a biopharmaceutical company late last year.

The Health Commission of Lanzhou, the capital city of Gansu province in China, confirmed that an outbreak had seen 3 245 people contract Brucellosis, which is often caused by contact with livestock carrying the brucella bacteria, or by drinking unpasteurized milk. Another 1 401 people had tested preliminary positive, though no fatalities have been reported. Authorities have tested 21 847 people out of the city’s 2.9 million population. 

The outbreak resulted from a leak at the Zhongmu Lanzhou biological pharmaceutical factory, which happened between late July to late August last year. The factory used expired disinfectants and sanitisers while producing brucella vaccines for animal use, meaning that not all bacteria were eradicated in the waste gas. The gas formed aerosols that contained the bacteria and leaked into the air, carried by wind to the Lanzhou Veterinary Research Institute, where the outbreak first hit. Infections at the institute started being reported in November, and by the end of December, at least 181 people at the institute were infected with brucellosis, according to Chinese state-run news agency Xinhua

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Other infected patients include students and faculty members at Lanzhou University, spreading to Heilongjiang province. 

An investigation was launched into the leak at the factory and by January, authorities had revoked vaccine production license for the plant, and withdrew product approval numbers for its two Brucellosis vaccines. In February, the factory issued a public apology and said that it would cooperate with local authorities in the response and cleanup efforts, and contribute to a compensation programme for the affected, which will be launched in batches starting in October. 

The Lanzhou Health Commission also announced that 11 public hospitals would provide free and regular checkups for the infected patients. 

What is Brucellosis?

The disease, also called Malta fever or Mediterranean fever, can cause symptoms including headaches, muscle pain, fever and fatigue. The duration of the disease can be anywhere from a few weeks to months to years. Some symptoms may become chronic and never disappear, like arthritis or swelling in certain organs, according to America’s Centers for Disease Control and Prevention (CDC). It can also damage the male testes, female ovaries and other reproductive systems.

Human-to-human transmission is rare, and most people are infected by eating contaminated food or breathing in the bacteria, which seems to be the case in Lanzhou.

Brucellosis was more common in China in the 1980s but infections have declined since the emergence of vaccines and better disease prevention and control. There have been a few outbreaks around the world in the past few decades; in Bosnia, a 2008 outbreak that infected about 1 000 people resulted in the culling of sheep and other infected livestock. In the US, about 60% of female bison in Yellowstone National Park carry the bacteria.