TOKYO -- The new coronavirus likely began spreading in China last fall, according to separate analyses of its genome by research teams in the U.K. and elsewhere.
These analyses, which cover all genetic information of the virus, indicate ongoing person-to-person transmission before the first patient was confirmed in the Chinese city of Wuhan. But no clues confirm where the virus came from or how it came to be, leaving an even deeper mystery.
Though evidence suggests the coronavirus originally came from bats, it remains unclear whether the virus was transmitted directly to humans or reached people through another animal.
The first confirmed patient with pneumonia caused by the coronavirus was identified Dec. 8, according to the city of Wuhan. Chinese doctors reported to The Lancet, a leading medical journal in the U.K., that this patient began exhibiting symptoms Dec. 1. But many question whether this was really the first case.
Teams worldwide are analyzing the genome of the virus to discover when it jumped to humans, and information is being collected in an international database. Tracing the mutations of the virus might reveal when person-to-person transmission began.
Researchers at University College London estimate that infections among people began between Oct. 6 and Dec. 11, based on genetic information of the virus drawn from more than 7,500 patients in China, Europe, the U.S. and elsewhere. The team suggests the virus spread beyond China early on and eventually triggered the pandemic.
A separate team at the U.K.'s University of Cambridge estimates that infections spread to people between mid-September and early December, based on a study of genetic material from about 1,000 people.
The Cambridge research also suggests the virus may not have originated in Wuhan.
The common ancestor to the new coronavirus, which is close to a type found in bats, seems to have originated in China, said Peter Forster, a fellow of the McDonald Institute for Archaeological Research at Cambridge. But this ancestor had been found more often outside of Wuhan, such as much farther south in Guangdong Province, until mid-January.
The search for when and where the outbreak started also has employed other types of analysis. Harvard University recently used satellite imagery to determine that the usage rate of parking lots at large hospitals in Wuhan increased significantly last August. Experts say that while this kind of analysis is inconclusive, the parking lot imagery could be related to COVID-19.
Reports also suggest the virus reached Europe and the U.S. and began spreading earlier than thought. The U.S. Centers for Disease Control and Prevention published an early report that said the disease may have begun spreading in the country between late January and early February.
In France, a man in his 40s was hospitalized with flu-like symptoms in late December. When a sample from him was analyzed in April, doctors confirmed he had been infected with the coronavirus. However, there was no surge in patients suffering pneumonia with an unknown origin, so this case's connection to the pandemic is unclear.
China originally said the virus began in Wuhan street markets but later issued a retraction. Beijing also has denied claims by the U.S. President Donald Trump's administration that the virus escaped from a Wuhan research facility.
The World Health Organization says it is unclear whether the virus originated in Wuhan markets. It is considering whether to dispatch a research team to assist international efforts to trace the virus to its origin, but finding the source will require the cooperation of and information from the Chinese government.