People walk on the footpath along the Yellow River in Lanzhou, northwest China's Gansu Province, June 11, 2020.  (Photo by Ma Xiping/Xinhua)

10,528 people in Lanzhou of Northwest China's Gansu Province returned positive antibody tests to brucellosis as of November 30 after a local Brucella leakage occurred between July and August in 2019, the Lanzhou government announced on Thursday.

As of November 30, Lanzhou carried out a total of 79,357 tests among locals, involving 68,671 residents. The number of people tested has grown because workers and temporary residents of Yanchang Road subdistrict in the city, the worst impacted area, as well as those who previously worked or lived there, were included in the testing in addition to local residents, the authority explained.

An expert team has been set up to engage in the treatment of people returning positive test results. So far, 1,604 people have received treatment, the authority said. 

From July 24 to August 20, 2019, the Zhongmu Lanzhou biological pharmaceutical factory, which is close to the Lanzhou Veterinary Research Institute, used expired disinfectant in its Brucella vaccine production, leading to the incomplete sterilization of waste gas from the production fermentation tank.

The waste gas carrying the bacteria-containing aerosols then spread to Lanzhou Veterinary Research Institute along with the prevailing southeast wind at that time, leading to infections, according to a report released by Health Commission of Lanzhou on September 15.

The report said it is an accidental incident — an exposure that occurred within a short period of time. 

Eight people from the company have been held accountable for the incident (either warned or fired from the company), the authority announced on November 5. 

The factory that caused the incident stopped its production on December 7, 2019. Its Brucella vaccine production license was withdrawn.

The first compensation fund of 10 million yuan ($1.52 million) was allocated on September 24 for monitoring, diagnosis, treatment and compensation for the people infected.

The compensation agreement was refined on November 24, alongside a supplementary agreement, which clarifies that Lanzhou factory is directly responsible for the incident, and promises that residents who suffer relevant symptoms in the future will receive free treatment and lifelong care.

As of December 2, 3,244 people had signed compensation agreements, the authority said.

Brucellosis is a zoonotic infectious disease caused by Brucella bacterium, which causes damage in the reproductive systems and joints of humans and animals. The incubation period for the disease can sometimes last from weeks up to months, according to experts.