Environmental biologists at the University of Stirling have warned that the potential spread of COVID-19 via sewage “must not be neglected” in the battle to protect human health.

The response to the global pandemic has focused on preventing person-to-person transmission. However, environmental biologists at the University of Stirling now believe the virus could also be spread though wastewater.

A new paper in the journal Environment International warned that the sewage system itself could pose a transmission risk. The authors of the study are calling for “an investment of resources” to investigate their concerns.

“We know that COVID-19 is spread through droplets from coughs and sneezes, or via objects or materials that carry infection,” said Richard Quilliam, who is currently leading a £1.85 million study into the transport of bacteria and viruses in marine environments. “However, it has recently been confirmed that the virus can also be found in human faeces—up to 33 days after the patient has tested negative for the respiratory symptoms of COVID-19.

“It is not yet known whether the virus can be transmitted via the faecal-oral route. However, we know that viral shedding from the digestive system can last longer than shedding from the respiratory tract. Therefore, this could be an important—but as yet unquantified—pathway for increased exposure.”

The authors of the peer-reviewed paper presented the example of the severe acute respiratory syndrome (SARS) outbreak in 2002-2003. The SARS-CoV-1, which is closely linked to the COVID-19 virus strain (SARS-CoV-2), was detected in sewage discharged by two hospitals in China.

Richard Quilliam authored the paper alongside Manfred Weidmann, Vanessa Moresco, Heather Purshouse, Zoe O’Hara, and David Oliver.

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The biologists said a lack of testing “makes it difficult” to predict the scale of the potential spread. The lack of testing also makes it difficult to determine the public health implications of the virus arriving at wastewater treatment plants.

The biologists added that the structural makeup of COVID-19—specifically its lipid envelope covering—suggests that it will behave differently in aqueous environments, compared to other viruses typically found in the intestine. There is currently limited information on the environmental persistence of COVID-19 but it is known that other coronaviruses can remain viable in sewage for up to 14 days, depending on the environmental conditions.

Risk of human exposure

“The transport of coronaviruses in water could increase the potential for the virus to become aerosolised, particularly during the pumping of wastewater through sewerage systems, at the wastewater treatment works, and during its discharge and the subsequent transport through the catchment drainage network,” according to the authors.

“Atmospheric loading of coronaviruses in water droplets from wastewater is poorly understood but could provide a more direct respiratory route for human exposure, particularly at sewage pumping stations, wastewater treatment works, and near waterways that are receiving wastewater.”

Risk could be further increased in parts of the world with high levels of open defecation, or where safely managed sanitation systems are limited and waterways are used as both open sewers and sources of water for domestic purposes.

“Such settings are commonly accompanied by poorly resourced and fragile healthcare systems, thus amplifying both exposure risk and potential mortality,” according to the authors.

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Richard Quilliam, lead author of the study, said the potential spread of COVID-19 in sewage “must not be neglected.” Image Credit: University of Stirling.

Investment

Currently, all published data on faecal shedding of SARS-CoV-2 is derived from hospitalised patients—with limited information available on mild and asymptomatic cases.

The paper concluded that “in the immediate future, there needs to be an investment of resources to improve our understanding of the risks associated with faecal transmission of SARS-CoV-2, and whether this respiratory virus can be disseminated by enteric transmission.

“Understanding the risk of spread via the faecal-oral route, while still at a fairly early stage of the pandemic, will allow more evidence-based information about viral transmission to be shared with the public.

“Furthermore, the risks associated with sewage loading during the remainder of the COVID-19 outbreak need to be rapidly quantified to allow wastewater managers to act quickly and put in place control measures to decrease human exposure to this potentially infectious material.

“At a time when the world is so focused on the respiratory pathways of a respiratory virus, understanding the opportunities for SARS-CoV-2 to be spread by the faecal-oral route must not be neglected.”

Header Image Credit: Centers for Disease Control and Prevention

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