Staff members disinfect a waiting room of Beijing Railway Station in Beijing, capital of China, June 18, 2020. Following the upgrade of emergency response to COVID-19 from Level III to Level II in Beijing, Beijing Railway Station has conducted strict measures to prevent and control the spread of the epidemic. (Xinhua/Chen Zhonghao)

Beijing's latest COVID-19 outbreak was caused by a virus strain from Europe, and transmitted through multiple exposure methods like contaminated environments and goods, the Chinese Center for Disease Control and Prevention (Chinese CDC) said on Friday, noting that the outbreak has been effectively controlled. 

The possibility that it may have been transmitted by animals to humans has been ruled out, and the Chinese CDC is currently investigating how the virus entered the market and its spreading mechanism.

According to an epidemiological investigation and analysis of viral gene sequencing results, the strain that caused the outbreak is the European branch I of the L genotype.

Chinese CDC also said it initially determined that the large-scale outbreak in Beijing's Xinfadi market was caused by exposure such as environmental pollution, objects, and personnel contact. The epidemic then quickly spread to more districts in Beijing and other provinces, leading to 29 Xinfadi-related outbreaks in other markets, households, and units.

The effects of the comprehensive prevention and control measures currently implemented in Beijing as well as other areas have already taken effect, and the risk of continued exposure to the relevant infected personnel has been basically eliminated, Chinese CDC said.

"The risk of subsequent new infections is low, and Beijing's outbreak has been effectively controlled," said the center.

The results of the high-throughput sequencing of the novel coronavirus genome from 52 confirmed cases in Beijing showed that all samples mutated at four sites, compared to the strain in Wuhan, according to Chinese CDC, adding the high-throughput genome-wide sequence of new coronavirus samples from the confirmed cases in North China's Hebei and Tianjin is identical to the genome-wide sequence of Beijing's samples.

This result shows that the virus detected in Xinfadi is completely different from the virus identified earlier in Wuhan, Central China's Hubei, as its strain is from Europe, suggesting that the imported products brought the virus to China and triggered the domestic transmission, Yang Zhanqiu, the deputy director of the pathogen biology department at Wuhan University, told the Global Times on Friday. 

Not just in Beijing, coronavirus was detected on the packaging of frozen white shrimps imported from Ecuador in Dalian, Northeast China's Liaoning Province, and Xiamen, East China's Fujian Province on Friday, prompting Chinese authorities to suspend imports from three shrimp producers in Ecuador.  

The CDC report shows that the virus samples mutated at four sites, making it more challenging to grasp the transmission rules of the virus, which is likely to mutate faster, Yang noted. 

While excluding the possibility of a virus spread from animals, it showed that it's either a pathagon or from a bat, but the virus detected this time in Beijing has nothing to do with animals, the expert added.

"While different types of novel coronavirus spread in different places, we may discover more new types in the coming months, as the virus has been mutating to adapt to different environments,"Yang said.

Beijing reported no new COVID-19 cases on Thursday, the fourth consecutive day. The capital reported its first new local COVID-19 case in two months on June 11, and as of Friday, the capital has reported 335 cases, with a majority linked to the Xinfadi market.