Authorities of the city of Lanzhou in northwest China on Tuesday confirmed that several thousand people have tested positive for a bacterial disease brucellosis due to a leak caused by a biopharmaceutical company in 2019.

According to CNN, people might have gotten infected by the disease either by consuming the contaminated food or by breathing in the bacteria.

The Lanzhou Veterinary Research Institute, situated in the Gansu province of China, in a press release said that it has set up a team to deal with the outbreak of brucellosis in the region. This disease happens when someone is in contact with livestock which is hosting the bacteria brucella.

The Lanzhou Veterinary Research Institute team headed by Secretary of the municipal party committee Li Rongcan and Zhang Weiwen, deputy secretary of the municipal party committee and mayor, the team will identify 11 public medical institutions to address the outbreak.

The release said, “As of September 14, 2020, a total of 21,847 people were tested, 4646 were initially screened positive, and 3,245 were confirmed by the Provincial Center for Disease Control and Prevention; 3,159 health files were established; a total of 23,479 consultations were held; 9 on-site medical diagnosis and treatment lectures were held and distributed.”

According to the team the outbreak resulted from the leakage of gas from the Lanzhou Biopharmaceutical Factory which also produces vaccine for the disease which infect animals primarily. “From July 24 to August 20, 2019, Lanzhou Biopharmaceutical Factory used expired disinfectants in the production of brucella vaccine causing incomplete sterilization of waste gas from production fermentation tanks, and the waste gas carrying bacteria-containing fermentation liquid formed bacteria-containing aerosols,” the statement said.

The statement pointed out that due to wind flow humans came into contact with the bacteria. “During the production period, the main wind direction in the area was southeast. In the downwind direction, human body inhalation or mucosal contact produced positive antibodies, resulting in a positive Brucella antibody incident… This incident was accidental and exposure (was for) a short time.”

According to CNN, several researchers working in the Lanzhou Veterinary Research Institute had fallen ill first after being exposed to the virus. Heilongjiang province, which is situated in northeast China, also saw infections due to exposure to brucella.

The United States’ Centers for Disease Control and Prevention (CDC) says exposure to brucella can lead to Malta fever or Mediterranean fever. The symptoms are usually headaches, muscle pain, fever and fatigue. The CDC says that even though the symptoms might subside eventually, there is always a risk of some of these symptoms to become chronic and patients can develop arthritis or swelling in certain organs.

Brucella outbreaks in China were on the decline since 1980s due to vaccine introduction as well as improved control measures but minor outbreaks have been reported over the past few decades.