Contaminated exhaust from a vaccine factory has been blamed for more than 200 cases of bacterial infection in Lanzhou, Gansu province, local authorities said on Thursday.

The infections were caused by the use of expired disinfectant at a factory that produces animal vaccines between July 24 and Aug 20, according to a statement from the provincial health and agricultural authorities and the government of Lanzhou.

The failed disinfections resulted in the brucella bacteria entering the exhaust emitted by the factory, a branch of China Animal Husbandry Industry Co, which infected students and faculty at Lanzhou Veterinary Research Institute of the Chinese Academy of Agricultural Sciences, which is near the factory, said the statement.

As of Wednesday, 181 students and faculty from the institute had tested positive for the brucella antibody since the first two cases were reported on Nov 28. Only one of them showed symptoms, though, the statement said.

Since December, 22 students and faculty of Lanzhou University also tested positive for the brucella antibody, among whom six had been to the institute. Another 13 cases in Heilongjiang province also worked at the institute in August.

The brucella bacteria, transmitted by contact with infected livestock including cattle and sheep or by eating unpasteurized dairy products, can cause brucellosis, also known as the Mediterranean fever.

Cui Buyun, a researcher in infectious diseases at the Chinese Center for Disease Control and Prevention, said patients with the disease can display symptoms such as fever, joint pain and sweating, but it is sensitive to antibiotics and rarely causes death or other serious consequences. There has been no reported human-to-human transmission of the disease, he said.

The workshop for producing animal brucellosis vaccines in the factory has been suspended from production since Dec 7. Local authorities have urged the factory to conduct thorough inspections and rectifications, and production will remain suspended until approval is received.

Major hospitals in Lanzhou have opened priority services so people living near the factory can receive free consulting, diagnosis and treatment, the statement said.

The bacteria that caused the infections was meant for the production of vaccines and was weakened in toxicity, so it generally will not cause symptoms in people infected after being transmitted over a distance. Cases with slight symptoms can recover with proper treatment, the statement said.

Xinhua contributed to this story.