COVID-19: Food safety risk?
The facts
The potential role of food in the Covid-19 pandemic and preventative measures
The COVID-19 pandemic has created unprecedented and unpredictable disruptions to every domain of social and economic life. Owing to the many sources of uncertainty revolving around the epidemiology, virology, and clinical medicine, no one can precisely calculate how long the medium and long-term ripple effects will last, and predict how long it will take to go back to pre-pandemic norms. Not surprisingly, this crisis has also created uncertainty in the security and safety of the food supply chain, with distinct challenges for farmers, distributors, producers, consumer- and packaged-goods companies, and retailers alike. Indeed the food supply chain and the food industry are in the spotlight due to the concern, at times amplified by the media, on the potential role of food in the transmission of infection to people.
Before going through some of these concerns, let’s have a look at the current scientific stances on the potential COVID-19 food safety risk.
The potential role of food in the COVID-19 transmission
Despite the large scale of the COVID-19 pandemic, currently, no sufficient and consistent information is available on the presence and survival of the SARS-CoV-2, the causing agent of COVID-19, in food. Moreover, there is no evidence that food has been a source or vehicle of infection for people, while it is known with certainty that most of the people currently ill have been contaminated by contact with other infected people and that the main person-person virus transmission is connected to the respiratory tract. The scientific response is provided by EFSA with a short note dated March 9, 2020: the Agency claims that ‘to date, there is no evidence that foods can pose a risk to public health with COVID-19’, hence the possibility of SARS-CoV-2 transmission through the food sector is considered negligible and mainly by secondary contamination’.
The same view is backed by the German Federal Institute for Risk Assessment (BfR), along with the FAO, FDA and CDC of the United States that jointly noted that, given the current state of knowledge, food is not a vehicle for the transmission of infection and that the risk of infection by the virus from food products, food packaging, or bags, and treated water, is thought to be very low’.
Furthermore, the experience of previous related human coronavirus (HCoV) outbreaks, such as SARS and MERS, demonstrates that there have never been proven cases of transmission through the consumption of food. Indeed, coronaviruses cannot multiply in food but need an animal or human host to effectively replicate.
However, given the unpredictable epidemiological development of COVID-19, and the high uncertainty on the alternative modes of transmission, more research and global collaborative efforts are needed to fill the plethora of scientific gaps.
While food has not been shown to be an infectious carrier for SARS-CoV-2, food plants have suffered widely publicised problems during the COVID-19 pandemic so far due to recently documented COVID-19 outbreaks among people who work in slaughterhouses and meat processing plants in the EU and elsewhere (i.e. the US and Canada). Although these plants continue to be important vectors for the spread of COVID-19, there is no evidence of the SARS-Cov-2 virus spreading to consumers through the food or packaging that workers in these facilities may have handled. Several factors contributed to the spread of the virus in the meat industry, such as the poor working, employment, and housing conditions affecting workers, lack of personal protective equipments (PPE), cold, and ventilation.
Risk amplification or real risk?
Below are the chronology and a brief explanation of reported events of frozen food and outer packaging found to be contaminated by SARS-Cov-2. These discoveries sparked media-amplified concerns that SARS-Cov-2 can spread on food surfaces and enter the food chain.
- China, June 2020: SARS-Cov-2 was detected on a chopping board used for imported salmon at the Xinfadi Market, Beijing’s largest wholesale food market. The imported salmon was from the Jingshen seafood market, which was shut down. Amid the concerns over food imports, the Chinese authorities strengthened the inspection of imported meat and vegetables and increased the screening of imported meat and seafood products. Although the detection sparked media concerns of salmon contamination, there is doubt on the salmon as the source of infection. Most likely, the used chopping board could instead have been contaminated with the deadly virus by an infected owner or customers, or other products that carried the virus. It is well known that beyond mammals, the novel coronavirus can hardly infect fish, birds, and reptiles, therefore it can’t be transmitted from fish to humans. Hence fishes could not catch the virus in their natural habitat, but is possible they can get contaminated by workers during their capture or transportation.
- China, since July 2020, SARS-Cov 2 was detected seven times on the packaging of imported frozen seafood products across several cities in China. On 3 July 2020, coronavirus was found on the container and the outer packaging of frozen shrimp imported from Brasil. The nucleic acid test (polymerase chain reaction-PCR) performed on the shrimp bodies and inner packages showed negative results. Due to concern over the risk of the SARS-Cov 2, this finding led to a preventative market measure of suspension of imports from three Ecuadorean shrimp producers.
- China, August 13, 2020: as part of routine screenings carried out on meat and seafood imports since June (when a new outbreak in Beijing was linked to the city’s Xinfadi seafood market, see above point), SARS-Cov 2 was detected on samples of frozen chicken wings imported from Brazil. While Brasil asked Chinese authorities to provide the results from laboratory tests, the Philippines imposed a temporary ban on poultry meat imports from Brazil, and Hong Kong halted chicken imports from the involved Brasilian facility.
Survival of SARS-CoV-2 on food and surfaces
To date, few studies have investigated the contamination and survival time of SARS-CoV-2 in feed and food. Some early information has been published regarding SARS-CoV-2 stability on surfaces and aerosols: the viable virus can persist for a limited time of up to 24 hours on cardboard, and up to several days on hard surfaces such as stainless steel (2–3 days) and plastics (3 days) in experimental environments with 40% of relative humidity and 21–23 °C of controlled temperature over 7 days. A further condition influencing the persistence is the inoculum shed. Besides this experimental condition, there is no evidence that contaminated packages exposed to different environmental conditions can transmit the infection. Theoretically, as with any other material that could have been contaminated by an infected person, whether it be a door handle or a package, the cross-contamination of food and/or packaging material by infective droplets can occur.
SARS-Cov-2 can also be transmitted from infected patients via the fecal-oral route. A recent report has documented that infection with SARS-CoV-2 is followed by persistent shedding of virus RNA in feces in high percentages of patients at densities until 7.5 log10 gene copies per gram. Importantly, a few studies have also detected live and culturable virus in feces, and the longer persistence of SARS-CoV-2 in the gastrointestinal system compared to the respiratory tract. These findings while confirming the possibility of the fecal route in the epidemiology of SARS-CoV-2 infection, have implications for: — areas with poor sanitation; — hospital environments where strict precautions must be taken in the management of patients infected with coronavirus and wastewater; — and any food production and processing environment where it is essential to apply good hygiene practices ( e.g. frequent hand washing and proper general hygiene).
Testing food and surfaces for SARS-Cov-2
SARS-CoV-2 surface and food testing is an important step in any food hygiene program aimed to prevent environmental virus circulation. The Surface (swab) qualitative testing for the target SARS-CoV-2 RNA can be used to validate and verify the effectiveness of sanitation standard operating procedures on a routine basis, or as follow-up in case of workers tested positive for COVID-19. Results can be negative or positive, with the latter meaning that the virus is not infectious but consists of RNA fragments only. Differently, a test conducted on food (and feed) can be used to check and monitor the level of contamination and the potential viral transmission through the related supply chains.
In terms of quantitative methods, so far, the SARS-CoV-2 viral load in the environment has been mainly quantified by specific realtime reverse transcriptase–polymerase chain reaction (RT-PCR), targeting RNA-dependent RNA polymerase and E genes, or by detecting viral proteins by western blotting. These methods are well established and validated, but they come with some weaknesses in case of high numbers of samples. Indeed, they are laborious, time-consuming, with low specificity, and expensive when there is a need to increase the sample sizes to perform the analysis in microtiter format, which is relevant under field conditions. These limitations make necessary the designing of an effective and rapid essay to detect (presence/absence) and quantify the surface/structural viral protein of SARS-CoV-2.
Introduction of SARS-CoV-2 in the environment and the food safety implications
One possible way by which SARS-CoV-2 can directly reach food products is the transmission from contaminated irrigation waters used on agricultural lands or sludge, which is typically applied as a soil amendment. The events recognize the transmission from human feces, through municipal wastewater treatment plants (WWTP) effluents (given it can survive the wastewater treatment process), and ultimately the introduction into the natural aquatic environment. Although SARS-CoV-2 is inactivated significantly faster than non-enveloped human enteric viruses with known waterborne transmission (such as adenoviruses, norovirus, rotavirus, and hepatitis A), as for others HCoVs (SARS and MERS) it can survive for extended periods in the aqueous environment. Infective HCoVs can be still detected in the effluent from WWTP: based on metagenomics, 80% of the samples from effluent Class B sewage sludge from 5 WWTP in the U.S. were found to contain coronaviruses. Similarly, SARS-CoV-2 was detected for the first time in untreated wastewater in Australia and in sewage from WWTPs servicing 6 cities and an airport in the Netherlands. These findings clearly signal the need to conduct wastewater surveillance of COVID-19 in the community in the framework of epidemiological monitoring of COVID-19 (the so-called wastewater-based epidemiology-WBE) and with the purpose to reduce virus circulation in the environment. Despite HCoVs are susceptible to inactivation by standard wastewater treatment protocols, the problem would mainly affect countries with substandard procedures and poor sanitization infrastructures, with the corresponding augmented risk of waterborne spread of SARS-CoV-2.
Another implication of the possible circulation of HCoVs in the natural environment is the uptake of the virus by the wildlife host, that can drink contaminated water and could subsequently serve as novel reservoir hosts for the virus (spillback into the human population). Hence the environments surrounding the WWPT could serve as potential areas where spillover into wildlife hosts, and should come under increased SARS-Cov-2 monitoring.
SARS-Cov 2 transmission via food: an unlikely scenario?
An unusual series of events would need to occur for the virus to be transmitted via the consumption of a food product. It is widely known that SARS-Cov-2 mainly spreads through the respiratory droplets produced when an infected person coughs or sneezes. Therefore, like other viruses, it may reach food products at any phase of the food chain (harvesting, preparation, processing, transport) or food packaging when an infected person sneezes or coughs towards food or packaging. As mentioned earlier, one important premise is that SARS-Cov 2 is an enveloped virus (the envelope is made of fat), thus less stable in the environment compared to non-enveloped human enteric viruses, and as such is vulnerable to all sorts of disturbances, including extreme changes in temperature and pH.
As more recently demonstrated, a moderate protein concentration in droplets markedly increases the infectivity of SARS-CoV-2, hence contaminated food and fomites could play a key role in the indirect transmission of COVID-19. Nevertheless, with proper food handling and sanitation, the likelihood of secondary contamination with SARS-CoV-2 should be negligible. In the event a food product becomes contaminated with droplets from an infected handler, coronaviruses can be inactivated by the heath (not viable SARS-Cov-2 was detected in virus transport medium after 30 minutes at 56°C and 5 minutes at 70°C), likewise SARS and MERS, so properly cooked food should be safe for eating. At room temperature coronaviruses can only survive on a contaminated surface for a few days, but they like the cold, and can survive at least two weeks at 4° C and at below freezing even longer than that.
The main concern is related to ready-to-eat food products, such as sushi, sashimi, and fresh meat (they are consumed without prior thermal treatment), that require additional sanitizing measures to guarantee food safety for consumers.
Based on these findings, the unlikely chain of events leading to human infection by the consumption of food carrying SARS-Cov-2 is the following:
- an infected person (asymptomatic or oligosymptomatic) eliminates the virus during the contagious windows (2 days before the onset of symptoms until 7–9 days after)
- the infected person handling/preparing foods could spread droplets containing viable and replicable viruses on the surface of food, or a package, and someone else could then contract the virus by touching the surface and then their mouth or nose
- or the consumer ingests the contaminated ready-to-eat food or foods not thoroughly cooked (the virus is destroyed by a temperature of 70°C)
- the virus survives to the ultra-acidic human digestive tract.
Good hygienic practices to prevent SARS-Cov-2 food contamination
The EU as well as national and international health organizations and institutions have adopted strict rules that guarantee a high level of food safety and that include biosecurity measures and good hygiene practices for both food workers and consumers.
Proper hygiene is essential not only to prevent COVID-19 but also other foodborne infections (e.g. Salmonella, E.coli, Campylobacter). There are many online manuals published by numerous international organizations, health agencies, and the European Commission targeting all operators involved in the stages of the food supply chain (producers, carriers, wholesalers, and retailers) as well as consumers. These manuals contain the measures for preventing COVID-19 infection and essentially refer to the existing hygiene practices and correct implementation of food safety management systems, mandatory for all food operators (e.g. HACCP).
Of particular relevance are the cleaning and disinfection procedures in establishments for equipment and the production of food between production lots; the prevention of cross-contamination between different types of food at different stages of the process; the personal hygiene, such as hand washing and disinfection; the use of sterile gloves and high-quality masks where required; the use of dedicated hygienic clothes and shoes, and staying away from work of unwell workers. These basic preventive rules apply to both food business operators and consumers.
For operators: regular and correct washing of hands when handling food products, both open and packaged, avoiding coughing and sneezing . This is because an infected person can contaminate food by preparing it with dirty hands or through infected droplets. Preventative measures may also consist of: — affixing a glass or transparent plastic screen between the employees and the customer: — maintaining a minimum distance between people, for example by marking the floor at certain intervals and limiting the number of people present: — availability of suitable hand disinfectants at the entrance and disposable gloves for handling fruit and vegetables: — regular disinfection of hand baskets, door handles, and shopping trolleys: — use of debit/credit cards and contactless payments as alternatives to cash.
For consumers: apply general hygiene rules in the kitchen, such as washing hands in clean water thoroughly before and after visiting food shops, correctly storing food, removing the outer packaging (e.g. cardboard or plastic) before placing the food in the refrigerator, and washing fruit and vegetables. Furthermore, it is necessary to avoid contamination from kitchen utensils (knives, dishes, etc.), which must be washed thoroughly with detergent or disinfection products, such as alcohol-based 60–70% or bleach, which are considered to be effective against SARS-CoV-2, or any other cleaning product that contains surfactants. Finally, as a general rule, the consumption of raw or undercooked animal products should be avoided. As with known coronaviruses, the SARS-CoV-2 virus is sensitive to cooking temperatures.
Take-home messages
- while instances of food packaging found to be contaminated by SARS-Cov-2 have been recently documented, there is no scientific evidence that contaminated food or packaging have been associated with the transmission of SARS-Cov-2
- considering the COVID-19 pandemic and the potential environmental circulation of SARS-Cov-2, observational/monitoring studies are needed to explore the virus transmission via food and survival on food packaging materials
- there is the need to develop an effective and rapid test for SARS-Cov-2 on food and feed to check and monitor the transmission through the related supply chains
- a developed and validated test SARS-Cov-2 will have beneficial effects on consumers and for the COVID-19 free certification of food industries
- SARS-Cov 2 poses challenges for the water and wastewater industries because of possible viral environmental circulation and subsequent contamination of food agricultural products and wildlife (spillback to humans).
