The Huanan Seafood Wholesale Market in Wuhan has been widely seen as the source of the deadly novel coronavirus infection or COVID-19 outbreak that has spread to 33 countries, infected nearly 79,000 people and claimed the lives of over 2,450. However, a new study suggests that while the infection rapidly spread within the market, it did not originate there. Rather, it was introduced to the market from another location.
"This assumption has not been fully validated because the Hua Nan market has not been confirmed as the single source of SARS-CoV-2 transmission to humans and other possible original sources of SARS-CoV-2 have not been identified in Wuhan yet," the study said.
For the study, the researchers sequenced the genomic data of 93 SARS-CoV-2 samples that were collected from 12 countries spanning four continents.
The infection did not originate at Huanan market
According to the study, a patient zero introduced the deadly pathogen to the traders and sellers at the Huanan seafood market. As a result of the massive footfall at the market, the transmission of the virus among sellers and buyers increased in early December.
"The crowded market then boosted SARS-CoV-2 circulation and spread it to the whole city in early December 2019," it said.
Two population expansions led to a wider spread
The study also suggests that COVID-19 witnessed two major population expansions — one on December 8, and the other on January 6. According to Chinese authorities and the World Health Organization(WHO), the first reported patient began exhibiting symptoms on December 8, following which, the cases confirmed showed links to the market in question. This implies that human-to-human transmission may have begun in late November or early December, and rapidly spread upon reaching the market.
"We suggest that SARS-CoV-2 may have already circulated widely among humans in Wuhan before December 2019, probably beginning in mid to late November. Some infected patients may have been overlooked because they had mild symptoms," the study said.
Another expansion could have been on January 6, 2020, owing to the holiday on Chinese New Year. It was on this day that a second-level emergency response was issued by the National Center for Disease Control and Prevention (CDC), warning citizens about the new infection, probably serving as a deterrent against travel and public gathering.
Patients from other countries
The study also said that among patients from the United States, Japan, France and Australia, there may have been at least two sources of infection. Specifically, the US has reported five sources, the authors wrote.
As the samples in other countries were limited, the infections were said to have originated from the same source. The scientists also said that some of the infections may have been contracted in Singapore and the Guangdong province in southern China, in addition to those who contracted it in Wuhan.
"We have found that some patients in Japan and United States might have been infected in Guangzhou, and one patient in France might have been infected in Chongqing or Singapore," the study said.