Researchers in China have warned that cold winter temperatures may accelerate the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and lead to new outbreaks of coronavirus disease 2019 (COVID-19).
The team’s review of studies assessing the factors that affect SARS-CoV-2 survival and transmission suggested that the virus can survive on the surfaces of cold-chain food items for more than three weeks.
Writing in the journal Frontiers in Public Health, the team from Weifang Medical University said: “We believe that the low-temperature environment in winter may accelerate the spread of the outbreak and that new outbreaks may occur.”
Recent detection of SARS-CoV-2 on imported cold-chain items
The SARS-CoV-2 virus is transmitted primarily through contact with contaminated droplets on surfaces or contact with an infected individual.
In China, where the COVID-19 outbreak was first reported, the epidemic was brought under control by April 2020, and the normalization of epidemic prevention and control was implemented in May 2020.
“The focus of normalized outbreak prevention and control in China includes the timely detection, isolation, and treatment of imported cases,” writes Yuhua Chi and colleagues.
Recently, SARS-CoV-2 was detected on the outer packaging of cold-chain items imported into the country and transmission events have occurred among staff members, say the researchers.
“This situation is of great concern and is receiving attention from relevant management and people in China, and corresponding countermeasures have been taken,” they write. “At present, there is an increased concern regarding the upcoming winter season and the potential of a new winter outbreak.”
What did the researchers do?
The researchers set out to analyze the factors involved in SARS-CoV-2 survival and transmission in different places and environments, with a focus on low temperatures and the surfaces of items.
They conducted a systematic search of PubMed, Web of Science, EMBASE, and CNKI on 25th November 2020 and identified a total of 368 relevant articles, thirty of which were selected for further analysis.
The study found that the amount of time SARS-CoV-2 can survive outside of the host is strongly influenced by environmental factors, including climate, light, temperature, and humidity.
“The higher the temperature, the more difficult it is for the virus to survive, with a temperature of 56°C for 30 minutes inactivating all viruses,” writes the team. “At a room temperature of around 25°C, viruses quickly lose their infectivity, but in winter, they survive longer.”
SARS-CoV-2 survives on packaging surfaces of cold-chain items for long periods
The researchers say studies have reported that around 90% of SARS-CoV-2 transmission can be attributed to symptomatic and asymptomatic carriers, with the remaining 10% attributable to environmental factors, including contaminated surfaces.
“Thus, person-to-person transmission of the virus in the food environment, including manufacturing, retail, and food service industries, remains the greatest risk,” they write.
One study published in Lancet Microbe found that refrigeration had little effect on SARS-CoV-2 infectivity when transported items were kept at 4°C for 14 days, which Zheng and colleagues say had not previously been expected.
In fact, one study published on the bioRxiv server found that storing SARS-CoV-2-contaminated chicken, pork, and salmon filets at −20°C for three weeks did not reduce viral titers or the virus’s ability to survive.
“Despite the protective effect of the −18°C cold chain environment on food, it is likely to lead to the prolonged survival of SARS-CoV-2,” writes the team.
“The virus can survive for a longer period of time on the outer packaging of items, suggesting that SARS-CoV-2 has the potential to be imported across borders over long distances, carried by cold-chain items,” says Zheng and colleagues.
The possibility of new outbreaks in Winter
The researchers say that at the start of the COVID-19 pandemic, it was too early to think that SARS-CoV-2 would become a seasonal virus.
However, a growing body of evidence suggests that small seasonal effects may lead to larger outbreaks in the winter, says the team.
“The winter world acts as a ‘large cold-chain environmental reservoir’ where SARS-CoV-2 can easily survive and spread,” writes Zheng and colleagues. “Combined with extreme winter weather and climatic conditions, frequent interactions between people indoors in poorly ventilated areas during the colder months could easily cause the spread of SARS-CoV-2, leading to outbreaks of COVID-19.”
The researchers suggest preparing for the arrival of winter by developing and strictly enforcing preventive measures and health policies, going out less, adhering to social distancing, wearing masks in public places, and maintaining hand hygiene.
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