The novel coronavirus that causes Covid-19 was detected on a chopping board for imported salmon at a market in Beijing.

The discovery was made as Chinese authorities searched for the source of new Covid-19 infections in the city, which saw Beijing shut down its largest wholesale market for vegetables and meat amid fears of a resurgence.

It has also locked down 11 residential communities in the vicinity.

At least 45 of the 517 samples so far collected from traders and employees at the Xinfadi market have tested positive for the virus.

Thousands of nucleic acid tests were being carried out among traders and customers who visited the Xinfadi wholesale market, and residents of the apartment complexes.

Major supermarket chains throughout the city have since stopped selling salmon as news of the new cases spread.

Prior to these new cases, Beijing, a city of some 21 million, did not report a new case for 55 days.

The streak was broken when a 52-year-old man, surnamed Tang, was diagnosed with Covid-19 earlier this week.

Within 48 hours, six new cases were diagnosed, leading to nucleic acid tests on their contacts.

The market came under focus after it was found out that of the first three cases, two had been to the market, and the third worked with one of them at a meat research institute, Chinese media reports said.

Here's what happened, in-depth

On Thursday, June 11, Xicheng District reported one new Covid-19 case -- a 52-year-old Beijing local, surnamed Tang.

Two close contacts, both of whom are Tang's family members, were put under medical observation.

Tests for both of them have come back negative.

Health authorities traced the source

On Friday, June 12, Beijing health authorities released the results of Tang's epidemiological investigation.

It showed that he had visited several places, including a shopping mall, vegetable market and entertainment venues in Fengtai District.

Two markets suspected

Beijing immediately shut down the beef and lamb trade center of wholesaler Xinfadi Market and Jingshen sea food market in Fengtai District where Tang had visited.

In total, six major wholesale markets in Beijing were suspended, or partially suspended, on Friday.

The novel coronavirus was also detected on a chopping board for imported salmon at Xinfadi market.

This discovery led to nine people being put into quarantine even though their test results were negative.

The imported salmon was from Jingshen seafood market, which was shut down on Friday.

Another individual who got Covid-19 went to the market

The authorities suspect that the Xinfadi market might be the source of the infection.

This was because Tang had gone to the market to buy meat on June 3, while another individual in China who also tested positive had collected samples of the market two days later.

This other individual was one of two new Covid-19 cases Beijing reported on June 12, resulting in two consecutive days of new coronavirus cases.

These two cases are colleagues at the meat research center in Beijing's Fengtai District.

Before this two cases, Tang's case reported on Thursday was the city's first domestically transmitted case in eight weeks.

These cases sparked fears of a second outbreak.

However, Chinese health experts believe sporadic cases are normal as the epidemic has not ended.

They have also judged a resurgence to be unlikely as the capital's 20 million residents are deeply aware of measures to be taken.

But this has still led Beijing on Friday to change its decision to reopen schools from first to third grades.

Local authorities have been urged to strengthen inspection of imported meat and vegetables to prevent them from becoming the "invisible virus transmission route".

Top photo via Global Times & Unsplash