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.
It is now 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. These observations have raised red flags about the possibility of fecal-oral and foodborne transmission of SARS-CoV-2.
How long do coronaviruses remain infectious on food surfaces?
Many 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.
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 their study, they used HCoV-229E as a surrogate for highly pathogenic human coronaviruses. Their study is published on the preprint server, bioRxiv*.
Viral infectivity declined within 24 hours in apples and tomatoes, while virus remained infectious at 72 hours in cucumbers
The researchers 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.
However, the experiments showed that the virus persisted in its virulent form even at 72 hours after inoculation on cucumbers. The 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.
Surface pH differences influence the stability of coronaviruses on fresh produce
According to the researchers, 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.
"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 authors feel 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.
Risk of coronavirus transmission through fresh produce contaminated during harvest is low
The results 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.
Findings may help foodborne transmission risk assessment and decision‐making
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.
"Potential foodborne transmission poses important public health implications and may partly explain the possible recurrence of the disease and its persistent transmission."
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.