Study On Potential Foodborne Transmission Of SARS-Cov-2 Thru Fresh Produce Shows That Coronaviruses Remain Infectious For Up To 3 Days On Cucumbers!
SARS-Cov-2 Foodborne Transmission
: A new Canadian study by researchers from Bureau of Microbial Hazards-Health Canada and the Faculty of Medicine-University of Ottawa on the potential foodborne transmission of SARS-CoV-2 through fresh produce shows that typical coronaviruses like the HCoV-229E strains remains infectious for up to 3 days on cucumbers.
Typically human coronaviruses (HCoVs) are mainly associated with respiratory infections. However, there is evidence that highly pathogenic HCoVs, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and Middle East Respiratory Syndrome (MERS-CoV), infect the gastrointestinal (GI) tract and are shed in the fecal matter of the infected individuals. These observations have raised questions regarding the possibility of fecal-oral route as well as foodborne transmission of SARS-CoV-2 and MERS-CoV.
Studies regarding the survival of HCoVs on inanimate surfaces demonstrate that these viruses can remain infectious for hours to days, however, to date, there is no data regarding the viral survival on fresh produce, which is usually consumed raw or with minimal heat processing. To address this knowledge gap, the study team examined the persistence of HCoV-229E, as a surrogate for highly pathogenic HCoVs, on the surface of commonly consumed fresh produce, including: apples, tomatoes and cucumbers. Herein, they demonstrated that viral infectivity declines within a few hours post-inoculation (p.i) on apples and tomatoes, and no infectious virus was detected at 24h p.i, while the virus persists in infectious form for 72h p.i on cucumbers. The stability of viral RNA was examined by droplet-digital RT-PCR (ddRT-PCR), and it was observed that there is no considerable reduction in viral RNA within 72h p.i.
The study findings were published on a preprint server and are currently being peer reviewed. https://www.biorxiv.org/content/10.1101/2020.11.16.385468v1
The human coronaviruses belong to the alpha and beta coronaviridae family. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes COVID-19, is a betacoronavirus that uses angiotensin conversion enzyme 2 (ACE-2) for entry into the host cell. ACE-2 is expressed abundantly in the epithelium of the human respiratory tract and the oral cavity and colon.
Currently, it is clear that about 30-50% of COVID-19 patients show gastrointestinal symptoms, including nausea, diarrhea, vomiting, and abdominal pain. Several studies report the detection of infectious SARS-CoV-2 RNA in the stool of over 50% of COVID-19 patients and have direct evidence for SARS-CoV-2 replication in human enteroids and enterocytes. https://pubmed.ncbi.nlm.nih.gov/32251668/
These observations have raised red flags about the possibility of fecal-oral and foodborne transmission of SARS-CoV-2.
Numerous studies regarding the survival of human coronaviruses on inanimate surfaces show that these viruses have the ability to remain infectious for several hours to days on surfaces. However, there is no clear data regarding the virus's survival on fresh produce that is usually consumed raw or with minimal processing.
Environmental persistence of HCoVs has been examined by different groups, who have obtained contradictory results. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7361302/
One research has shown that the stability of SARS-CoV-2 and SARS- CoV-1 on dry surfaces at RT(room temperature) is similar, with no infectious virus being retrieved after 72h p.i.
However in another study it was shown that recovered infectious SARS-CoV-2 from plastic and stainless steel was infectious up to 7 days p.i. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7214863/
Yet another study reported that HCoV-229E remains infectious for 5 days at RT on a range of surface materials including glass and PVC, while it is rapidly inactivated on the surface of copper alloys.
In another study, more relevant to this work, it was shown that the infectivity of HCoV-229E is completely abolished within 4 days p.i. on lettuce at 4°C. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7091382/
Recently, it was demonstrated that SARS-CoV-2 remains infectious on salmon at RT for 2 days. https://www.biorxiv.org/content/10.1101/2020.09.06.284695v1
In order to address this gap in knowledge, researchers from the Bureau of Microbial Hazards, Health Canada, and Faculty of Medicine, University of Ottawa examined the survival of human coronaviruses on the surface of fresh produce such as apples, cucumbers, and tomatoes.
In the research the study team used HCoV-229E as a surrogate for highly pathogenic human coronaviruses.
Interestingly viral infectivity declined within 24 hours in apples and tomatoes, while virus remained infectious at 72 hours in cucumbers.
The study team demonstrated that the infectivity of the virus declined within a few hours after inoculation on apples and tomatoes. Also, at 24 hours post-inoculation, no infectious virus could be detected in apples and tomatoes.
Significantly however, the experiments showed that the virus persisted in its virulent form even at 72 hours after inoculation on cucumbers. The study team used droplet-digital RT-PCR to examine the stability of viral RNA and observed that there was no significant reduction in viral RNA within 72 hours post-inoculation.
Accordingly, the more prolonged survival of the virus on cucumbers compared to tomatoes and apples could be partly due to the surface pH differences of these vegetables. Studies examining the influence of pH on the stability of coronaviruses have shown that coronaviruses are more stable around neutral pH as compared to alkaline or acidic pH. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7361302/
Corresponding author Dr Neda Nasheri from the Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, University of Ottawa told Thailand Medical News, "At this point, we speculate that the longer survival on cucumbers compared to apples and tomatoes could be partly explained by the difference in surface pH of these commodities."
The study team feels that further investigation is necessary to determine if the surface of apples and tomatoes has any virucidal properties that may trigger rapid inactivation of the virus.
The study findings agree with previous findings that showed that the infectivity of human coronaviruses declined within a few hours to days on inanimate surfaces at room temperature. Thus, if fresh produce is contaminated with human coronaviruses through infected hands or other means during harvest, as long as they are stored at ambient temperature, the risk will be considerably low by the time it is delivered to the consumers.
However, if the contamination happens towards the end of the food processing chain, for example, through an infected staff in a restaurant, where the food is consumed within a few minutes of contamination, the potential risk for infection is high. The authors believe that such situations also run a risk of becoming super-spreading events.
These study findings may help foodborne transmission risk assessment and decision‐making.
Importantly the persistence of viral RNA on produce for several days even after losing their infectivity could be attributed to the high environmental resilience of the coronavirus shell, which is responsible for the protection of the viral genome. Considering the public health implications of foodborne transmission of SARS-CoV-2, the authors hope that their results could aid risk assessment and robust decision‐making concerning the foodborne transmission of human coronaviruses.
The study team concluded, "Potential foodborne transmission poses important public health implications and may partly explain the possible recurrence of the disease and its persistent transmission."
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