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Authorities in China say that a coronavirus patient was infected after just 15 seconds of contact with a sick person.

Officials said that a 56-year-old man in the eastern province of Zhejiang was caught on surveillance cameras visiting a vegetable market late last month.

At the time the man had no symptoms, and had not come in contact with any infected people or traveled outside of his region during the previous 14 days. But he was seen standing next to a woman in a market stall for 15 seconds before departing again without buying anything.

The woman has since been shown to have had the virus at the time. Neither was wearing a mask. On Tuesday the man was diagnosed with coronavirus and quarantined.

The details of the infection were reported by the Jiangbei health commission in the coastal city of Ningbo in eastern China and reported by Chinese state media. It is unclear how the local health commission concluded that the market encounter was the source of the man’s infection.

A day later, officials in Zhejiang announced severe travel restrictions in Ningbo and three other cities in Zhejiang province — even though the region has yet to record a single death from the virus and is over 350 miles from the epicenter in Hubei, where 14 cities and 50 million people are in lockdown.

A second case of rapid infection was reported in Zhejiang on Wednesday.

A man in Hangzhou was reportedly infected after spending just 50 seconds with a confirmed patient at a hospital in the city when neither of them were wearing masks, based on surveillance camera footage reviewed by officials. Again, the man had no prior contact with infected patients and had not traveled outside the region, according to a report by Beijing Evening News.

Authorities in Zhejiang have shut down public transport, closed “unessential” public venues — and even banned funerals and weddings — in the cities of Ningbo, Wenzhou, Hangzhou, and Taizhou, which have a combined population of around 30 million.

Each household has also been issued a “passport” that allows just one person per home to go outside every two days to buy necessities.

Chinese authorities, stinging from criticism that their delayed response to the outbreak allowed it to spread so quickly, have been taking drastic measures to try to contain the epidemic — but so far these measures are just not working.

On Thursday the death toll spiked again with 73 new cases, bringing the total to 565. Confirmed infections have now passed 28,000 — the youngest of whom is a newborn baby — with another 25,000 suspected cases.

But, a public health expert in London, who has been modeling infection rates in China, suggests that the official figures are publicizing only a small fraction of the overall infection rate because authorities there are focusing on only the severe infections.

“We think 10% or less of all infections in China are being detected at the current time,” Neil Ferguson, a professor at the faculty of medicine at Imperial College London, said in a video posted on YouTube. “The next step down is what is being detected overseas, there we think sensitivity is somewhat higher, but still we may be detecting only a quarter of all infections.”

Ferguson added that “we estimate that maybe up to 50,000 new infections a day occurring in China which is obviously much larger than the official case numbers. We think the epidemic is roughly doubling in size every five days.”

“It is hard to evaluate how effective controls are, but there is limited evidence of it slowing in China,” Ferguson said.

Ferguson said that the infection rate is likely to peak in Hubei province in about a month and in the whole of China a month or two after that.

Internationally, the virus continues to spread, with 216 cases confirmed in 24 countries, including deaths in Hong Kong and the Philippines.

On Thursday Saudi Arabia became the latest country to suspend travel to China, and at least nine countries are denying entry to travelers from the country — including the U.S.

KLM and Air France added their names to a list of at least 25 airlines that have suspended or reduced flights to and from China. However, given how porous international borders are, and how long it takes for symptoms of the coronavirus to appear, the threat remains.

“The rest of the world will see epidemics at various times after [the peak in China] depending on how many travelers have come to [the countries] in the past few weeks from China,” Ferguson said.