Thousands of people in northwest China have tested positive for a bacterial disease after a leak from a state-owned biopharmaceutical plant making animal vaccines last year.

Health officials in Lanzhou city said 3,245 people had contracted brucellosis, a disease often caused by close contact with infected animals or animal products.

Another 1,401 people tested as an early positive for the disease, and health authorities said there was no evidence of person-to-person transmission so far.

What is brucellosis?

Brucellosis is a bacterial disease caused by various Brucella species, which mainly infect cattle, swine, goats, sheep and dogs. Humans generally acquire the disease through direct contact with infected animals, by eating or drinking contaminated animal products, or by inhaling airborne agents. 

The majority of cases are caused by ingesting unpasteurised milk or cheese from infected goats or sheep. Person-to-person transmission is rare. The disease causes flu-like symptoms, including fever, weakness, malaise and weight loss.

How people were infected?

Chinese authorities found a biopharmaceutical plant had used expired disinfectant in its production of Brucella vaccines for animals between July and August last year. 

Contaminated gas from the China Animal Husbandry Lanzhou Biopharmaceutical Factory in Lanzhou formed aerosols containing the bacteria, and this was then carried by wind to the Lanzhou Veterinary Research Institute, infecting nearly 200 people there as of December last year.

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