File Photo:Xinhua

Studies on the evolutionary relations between the novel coronaviruses have provided more clues, suggesting it's still difficult to determine the origin of the virus, while experts called for more solid and authoritative researches. 

The US has found at least four COVID-19 cases of unknown source, media reported Saturday.

"The two concerns should be put together to consider to avoid arbitrary information without adequate evidence," Zhang said.

An English paper submitted by Yu Wenbin, an associate researcher at the Chinese Academy of Sciences, to ChinaXiv on February 21 indicated that the Huanan Seafood Market in Wuhan, the epidemic epicenter, might not be where the virus was originally from.

The article said the haplotypes of the 58 new coronaviruses, numbered H1-H58, were divided into five groups: A, B, C, D, and E, with A being the oldest and E the youngest.

However, in Hubei, only coronavirus from Group C are detected, but in the US the viruses from all five groups have been found.

Therefore, Yu and his colleagues believe that the novel coronavirus which caused the epidemic in Hubei might be imported from some other places.

Zhou further explained that the research is science based. "If all the test results of novel coronavirus in the US are found to be Group C, then it might be transmitted from China. But if not, it might be local."

The article was echoed by Pan Hwai-tzong, a pharmacologist in Taiwan in a recent local TV show, who noted that more multiple genetic types of the new coronavirus have been found in the COVID-19 cases in the US than those in the Chinese mainland.

Wuhan virologist Yang Zhanqiu told the Global Times on Saturday that unknown cases of the US influenza deaths need further retrospective examination before a conclusion could be made where it originated.

More inexplicable evidence is complicating COVID-19 knowledge.

The Lombardy outbreak in Italy was from a man who never met anyone from China, local media la Repubblica reported.

A patient in California diagnosed with coronavirus infection did not travel anywhere known to have the virus, the US Centers for Disease Control and Prevention announced Wednesday night. The patient was also not exposed to anyone infected.