A team of Chinese researchers has found the coronavirus that causes Covid-19 can survive for more than a week on the surface of chilled fresh salmon, raising implications that it could be a source of international transmission.
The experiment discovered that the virus remained infectious for eight days after being kept at a temperature of 4C.
The experiment also found that Sars-CoV-2, the official name for the virus, remained infectious on the salmon for two days at 25C, which the researchers called "regular room temperature".
Salmon is typically kept at 4C in markets, restaurants and during transport, extending the virus's lifespan by six days. High-quality salmon can be moved across the world in a matter of days. For instance, Chile's fishing authority said last year that salmon could reach Shanghai in two-and-a-half days.
"Under such condition, [coronavirus] contaminated fish from one country can be easily transported to another country within one week, thus serving as one of the sources for international transmission," said the Chinese scientists led by Dr Dai Manman in a non-peer-reviewed paper published in biorxiv.org on Monday.
"This calls for strict inspection or detection of [the coronavirus] as a critical new protocol in fish importation and exportation before allowing sales."
Two of China's coronavirus outbreaks - the initial outbreak in Wuhan and a later spread in Beijing in June - have both been associated with wet markets that sold seafood.
The first strain of Sars-CoV-2 was detected in the Huanan Seafood Market in Wuhan at the end of last year. Numerous international studies suggested the virus emerged elsewhere, most likely outside Wuhan.
China temporarily halted salmon imports in mid-June after the virus was reportedly discovered on salmon chopping boards at Xinfadi market, the centre of the Beijing outbreak. Authorities later ruled out salmon as the source of transmission.
The cases in Wuhan and Beijing created "concerns that fish or meat-attached Sars-CoV-2 could be a potential source of Covid-19 transmission", wrote Dai, associate professor with the South China Agricultural University in Guangzhou.
Additionally, the scientists cited other countries finding Sars-CoV-2 on meat or in meatpacking employees as a reason to investigate the virus's survival time on salmon.
Link probed in Auckland cluster
Links to transport of chilled food have been investigated in the re-emergence of Covid-19 in Auckland.
A month on, where the first person became sick still remains a mystery.
The earliest known case in the current wave has been pinpointed to a worker at an Americold cool store in Mt Wellington who fell ill on July 31, however testing of surfaces there has revealed no trace of the virus, despite Dr Ashley Bloomfield telling NZ in August: "We know the virus can survive within refrigerated environments for quite some time."
- South China Morning Post, additional reporting NZ Herald