The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has rapidly infected over 191 million individuals across the world since its emergence in late December 2019. The virus causes COVID-19 (coronavirus disease 2019), which alone is responsible for over 4.1 million deaths during this period, crippling the global economy.
Generally, the main routes of transmission for SARS-CoV-2 are direct transmission via aerosolized droplets and direct contact. However, concerns have been raised about potential virus transmission through food, food packaging, and common food contact surfaces.
As with other viruses, including non-enveloped viruses such as norovirus and rotavirus as well as enveloped viruses such as influenza virus, fomite-mediated transmission could also be an important secondary method of transmission for SARS-CoV-2.
Even though public health measures were taken to control viral transmission, a clear understanding of how widespread the fomite-mediated transmission is not available.
To shed more light on the transfer of viruses that might lead to infections, a recent study focused on whether human coronaviruses can transfer efficiently from contaminated hands to food or food contact surfaces.
Researchers from the National Food Virology Reference Centre, Bureau of Microbial Hazards, Health Canada, and the University of Ottawa tested the transfer of viruses from the contaminated hands onto different surfaces.
“This study aimed to address how efficiently contaminated hands can transfer the infectious virus to a surface.”
This study, published in the journal Viruses, indicated that human coronaviruses do not transfer effectively from contaminated hands to contact surfaces without the presence of any organic material.
Figure 1 Amount of infectious virus of HCoV-229E, HCoV-OC43 and MNV-1 transferred from artificially contaminated gloved fingertip to the four surfaces tested, and from direct swabbing of fingertips prior to transferring to the surfaces. Different number of asterisks indicate samples that are either not statistically different (same number of asterisks) or are statistically different (different number of asterisks) at p = 0.05.
For this study, the researchers chose surfaces such as stainless steel (Grade 304 (UNS S30400)), high-density polyethylene (HDPE) as a representative of plastic, English cucumber, and Royal Gala apples. HDPE is regularly used in the food industry and packaging.
Using a dried viral droplet on a fingertip (nitrile-gloved finger), they pressed the fingertip on these surfaces for 10 seconds and then tested these surfaces for the virus.
They employed three viruses in the study: two human coronaviruses, 229E and OC43, and murine norovirus-1 (MNV-1), as a surrogate for human norovirus, which is a contagious gastroenteritis-associated pathogen.
“The use of surrogates allows for expanding the current knowledge of HCoV, without the need for more stringent biosafety measures required to work with the more pathogenic HCoVs,” observed the researchers in their paper.
In addition, they discussed the similar physicochemical and immunogenic properties of these viruses.
The coronaviruses 229E and OC43, like SARS-CoV-2, are commonly associated with the common cold, typically characterized by rhinorrhea, nasal congestion, sore throat, sneezing, and cough, with or without fever. They included murine norovirus-1 in this study to compare enveloped viruses to non-enveloped viruses.
The researchers determined and tabulated the limit of detection for the detection methods on each surface used for the three viruses in this study for reference.
Here, the researchers observed that for HCoV-229E and HCoV-OC43, when using maintenance media as the transfer matrix, there was no detectable transfer from a contaminated hand to the fomites. However, they found that MNV-1 transferred under the same conditions. This is suggestive that the HCoVs transfer poorly via fomites, particularly when no organic matter is present.
“Because they are more resistant, non-enveloped viruses may have a better ability to remain infectious during drying steps, or during the transfer to surfaces, and may survive longer than enveloped viruses such as HCoVs,” reasoned the researchers.
These findings indicate that the fomite-mediated transmission of HCoVs, including SARS-CoV-2, from a contaminated hand may not be efficient. Therefore, during this pandemic, fomites may be carrying respiratory droplets or oral mucosa from an infected individual - which can be strictly avoided by the use of masks and gloves.
Further, it is well established that an infected individual sheds the coronavirus in the fecal matter. This study confirmed the successful transfer of the HCoV-OC43 to three of the four tested surfaces when an organic fecal material was used as the transfer matrix instead of maintenance media.
“If an individual shedding coronavirus in their feces does not follow proper hand hygiene, it is possible that they could transfer the virus to food and fomites.”
The researchers found that the most efficient transfer of the virus occurred on the stainless steel or cucumber and then typically followed by apple. They noted that for MNV-1, the transfer was most efficient to stainless steel, cucumber, and apple, in the decreasing order of transfer efficiency.
The HCoV-OC43 organic transfer occurred the most efficiently onto the cucumber. Significantly, they demonstrated that for both viruses, transfer to plastic did not occur. They explained the difference in the observations between steel and plastic to the surface porosity. “Viruses, in general, seem to be able to transfer more efficiently to non-porous surfaces and survive longer on these surfaces,” they elaborated.
The study finds that human coronaviruses are unlikely to spread from hands to food packaging and foods, so the risk of spreading the virus via this mode is low. When the virus is present in organic material, such as feces, the transfer becomes significantly more efficient. Further exploration of this interaction is necessary to determine whether fecal HCoV contamination affects viral survival and infectivity. The practice of proper hand hygiene should continue as it is sufficient to prevent the spread of viral infections even if fecal contamination exists.
The important inference from this study in the face of the ongoing pandemic is the reaffirmation that 1) mandatory masking helps, as fomite-mediated viral transmission by contaminated hands is poor, and 2) proper hand hygiene prevents efficient viral transfer because only within the organic material the viral transfer is significant.