Possible Coronavirus Transmission Linked to Frozen Food

Viruses can often lay dormant while frozen and then begin infecting a host once defrosted.
Viruses can often lay dormant while frozen and then begin infecting a host once defrosted.

In Tianjin city just outside of Beijing, a coronavirus case is leading experts to question whether the patient contracted COVID-19 from frozen fish. This is a worrying turn of events after months of advice that the coronavirus could not be easily transmitted through food or its packaging.

The case in question involves a 22 year old man who worked at the Conrad Hotel in Tianjin. His role primarily involved washing dishes but he also sometimes washed frozen fish. After contracting COVID-19, authorities were not able to determine any contact between the man and any known or suspected cases of the disease, and have also confirmed that the man had not travelled within the past 14 days. He had however, washed frozen fish - and Chinese health officials say the virus was found on chopping boards used to cut up imported salmon at the Xinfadi market, which supplies more than 70 percent of Beijing’s fresh produce. A current cluster from the market is thought to be linked to 158 people who have contracted COVID-19 in an ongoing outbreak in Beijing.

Yang Zhanqiu, a virologist at Wuhan University, has speculated that the man may have become infected by handling the food or even the ice used to freeze it.

Could COVID-19 Be Transmitted Through Frozen Food?

Unlike with bacteria, refrigerating or freezing viruses, including coronaviruses, doesn’t necessarily kill them. Instead viruses often lay dormant while frozen and then begin infecting an animal or human host once defrosted.

All known evidence so far suggests that receptors for the coronavirus only exist on mammals including humans, and it’s not possible for fish to be infected with the disease.

However, it’s possible that the virus could be transmitted onto the fish by humans when catching, transporting or handling the fish - then it could lay dormant during the freezing process - only to find a new human host during the thawing or preparation stage. Given that the coronavirus was found on chopping boards used to cut up imported salmon on the Xinfadi market it’s not too far-fetched to think this may be what’s happened.

However, the theory should not yet be accepted as the correct source of transmission. Shi Guoqing, the deputy director of China’s Centre for Disease Control and Prevention (CDC), said there was “no evidence” salmon was the immediate source of the outbreak.

The Beijing Outbreak

The current outbreak in Beijing is the first serious cluster since March when the Chinese government declared victory over the coronavirus, and has led to mass testing and lockdowns in Beijing and surrounding areas. At least 158 cases have been reported with most being able to be traced back to the Xinfadi market. The market supplies more than 70 percent of Beijing’s fruit, vegetables, seafood and meat and is used by tens of thousands of people every day.

A number of those tested have been asymptomatic. Beijing officials said Saturday that 45 workers at the Xinfadi market tested positive for the coronavirus though they showed no symptoms. Wet markets are thought to be emerging as hot spots for the coronavirus as the produce is stored at low temperatures in wet conditions - ideal conditions for the virus to survive.