LANZHOU -- A total of 6,620 people have been confirmed antibody-positive for brucella since contaminated factory exhaust caused infections in 2019 in Lanzhou, capital of Northwest China's Gansu province, local authorities told a press conference on Thursday.

The infections were caused by the use of expired disinfectant between July and August 2019 at a factory that produces animal brucellosis vaccines. The failed disinfections resulted in the bacteria entering the exhaust emitted by the factory.

The Lanzhou municipal government said it has conducted tests on 55,000 people, accounting for 97.5 percent of the population in the Yanchanglu sub-district, where the factory is located.

As of Wednesday, 337 people received compensation from the factory, which allocated 10 million yuan (about $1.5 million) to a special account.

Authorities said they would continue to conduct free testing, and offer free treatments to those who are tested antibody-positive and develop symptoms. They will also ensure long-term health follow-up and take a lifelong responsibility for them.

At the press conference, officials also said dismantlement of the factory was completed on Oct 8, and construction of a new factory site is near completion.

Brucella, transmitted by contact with infected livestock including cattle and sheep or by eating unpasteurized dairy products, can cause brucellosis, also known as Mediterranean fever. It is characterized by fever, malaise and headaches. The risk of human-to-human transmission is said to be minimal.