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China Has A Theory About Its New COVID-19 Cases. Many Scientists Are Skeptical

Taking swab samples from agricultural products at the Xinfadi wholesale market in Beijing.
Taking swab samples from agricultural products at the Xinfadi wholesale market in Beijing.

China now reports few to none domestically transmitted COVID-19 cases — only 12 cases were reported on Dec. 15.

But a flurry of recent cases has Chinese public health officials worried. They claim that the cases stemmed from workers who had contact with imported food and packages.

Beijing has now banned nearly 100 suppliers from 20 countries and at one point recommended travel restrictions in at least two cities where frozen food handlers contracted the coronavirus.

There's a problem with this theory. The cases directly contradict international health guidance, which says such transmission is highly unlikely. Emanuel Goldman, a microbiologist at Rutgers University's New Jersey Medical School, wrote in the Lancet this summer that "the chance of transmission through inanimate surfaces is very small," adding that objects not "in contact with an infected carrier for many hours do not pose a measurable risk of transmission in non-hospital settings." Since then, Goldman told NPR that more research has come out to corroborate his claim.

What is going on? Here's what we know about the subject of transmission via fomites — objects contaminated with viral particles.

Is it possible to contract COVID-19 from touching food packaging?

"There is a theoretical possibility of catching the virus that way," says Professor Goldman of Rutgers. "It's not impossible."

But, he emphasizes, "It's unlikely."

"I think most scientists would agree with that," he says.

Why so unlikely? First, you'd have to touch a freshly contaminated surface, Goldman explains. Like a doorknob. Or food packaging.

Then, "you have to touch your face" without having washed your hands. And specifically, the mouth, nostrils or eyes — the entry points for the virus.

The World Health Organization uses the phrase "highly unlikely" to describe the chances of contamination from food packaging — but with an abundance of caution urges that the food industry "reinforce personal hygiene measures" for employees.

China concurs.

The Chinese Center for Disease Control and Prevention has said there is a "very low risk" of infection from frozen foods.

But it doesn't agree 100%. China's CDC claims that it has identified one case in which live viruses were carried into China via the cold surfaces of imported items and later infected workers. The organization warned workers handling foods stored in refrigerated conditions that they are at "a relatively high risk" of getting the coronavirus and should increase their efforts to protect themselves.

What's the science behind China's claim that people have been infected with SARS-CoV-2 by touching contaminated objects?

China has reported at least four clusters of cases since this summer that it attributes to virus-contaminated objects that have traveled from virus-stricken countries and regions.

In November, Shanghai health authorities stated that seven cases were linked to the city's Pudong International Airport. They claim that the source is a shipping container from North America, which two of the seven patients entered to clean without masks. The other five infected individuals include those who also worked in the airport freight section as well as their spouses.

The port city of Tianjin also identified two new COVID-19 patients earlier that same month. A Tianjin CDC official, Zhang Ying, said both individuals, a warehouse loader and a truck driver, had been in physical contact with a shipment of hog heads from North America. According to CCTV footage, officials said the truck driver, not wearing any personal protective equipment, picked up a hog head when it fell out of the warehouse.

The frozen meat and its package have yet to be tested to this day, but Zhang said samples taken from the spot where the pig head fell on the ground came back positive for the coronavirus. There was also a genetic match to the samples taken from the two patients.

The biggest cluster of cases that Chinese researchers are linking to fomite transmission came in June. More than 300 people connected to the Xinfadi Agricultural Wholesale Market, a sprawling facility that supplies 90% of all fruits and vegetables in Beijing, became ill.

Investigators took 1,900 samples from various places in the market. They reported that about 40 came back positive for the coronavirus, including a sample from a cutting board used to chop salmon. Overnight, salmon of all sorts was dumped from supermarkets and restaurants out of fear that consuming salmon may lead to infection — despite expert guidance that salmon cannot be infected and then pass the virus on to humans who eat its meat.

The exact origin of the Xinfadi cluster is still unclear. But a team of Chinese researchers from Tsinghua University, the Beijing CDC, and the Chinese Academy of Medical Sciences jointly published a study in October positing that based on genome sequencing results, this particular strain of the virus has European origins. They concluded that the source of the Xinfadi cases was likely "imported food via cold-chain logistics." And while the same researchers concede that it is not clear whether the amount of virus found in the sample from the salmon cutting board was enough to infect a person, "the risk from food and environment contamination exists."

Goldman isn't convinced. He points out that the Xinfadi study found only viral RNA, or genetic remnants of the virus. That would only indicate that the coronavirus was present on the surface some time prior to testing. A test for live viruses, on the other hand, would strengthen the case for fomite transmission.

"The virus is fragile. It does not survive very well outside the human body," Goldman explains. "Without a test for infectious virus, it doesn't really tell you anything."

But in one instance, the Chinese CDC claimed to have done precisely that. A small cluster of COVID-19 cases was discovered in the port city of Qingdao in early October. Health officials traced the source to two dock workers being treated at a local hospital for the virus after unloading frozen imported codfish in September. Subsequent testing in October by the Chinese CDC found live coronavirus samples on the packaging. "Being able to isolate live viruses [from samples] this time means there must exist living viruses that spread and infect," said Gao Fu, director of the Chinese CDC, during an Oct. 17 press conference.

The following month, a team of researchers, including Gao, published its findings in Biosafety and Health,a peer-review journal managed by the National Institute for Viral Disease Control and Prevention and the Chinese CDC. When 421 surface samples were taken for codfish packages, 50 tested positive for viral RNA, and only one later proved to be infectious.

"I don't think this changes anything for ordinary folks in the real world, who will not be dealing with imported frozen packaging directly upon receipt of shipment. All the other tests the Chinese have done further downstream after receipt of imported packages have been negative for live virus," Goldman told NPR after reviewing the article. "This paper is kind of like a proof of principle. Yes, [fomite transmission] could happen, but it's still very rare."

What has China done to prevent fomite transmission?

The State Council has already suspended imports from nearly 100 suppliers in 20 countries where outbreaks were reported among factory workers. It also issued nationwide regulations stipulating that all imported foods that require cold storage, as well as their storage facilities, be thoroughly disinfected before the products are unloaded and handled by movers. All goods must also be tested for the coronavirus upon arrival at the port of entry.

So far, among the 873,475 samples customs officials have swabbed from imported products, 13 have tested positive for viral RNA.

The measures have created private furor among diplomats and importers, who dispute that their food products are spreading the coronavirus.

Reuters reported that behind a closed-door WTO meeting in November, China's major trade partners such as Canada pushed China to stop its stringent testing regiment, at least not without demonstrating a science-based explanation.

The U.S. Department of Agriculture said it also prodded China on two occasions to match its trade restrictions with an accurate assessment of risk, adding that Beijing's most recent COVID-19 trade regulations "are not based on science and threaten to disrupt trade."

So far, China has remained steadfast in upholding its policies, which it argues are rooted in science and designed to "protect people's lives to the maximum extent."

Amy Cheng contributed research from Beijing.

Copyright 2021 NPR. To see more, visit https://www.npr.org.