COVID-19 transmission risk via sewage "must not be neglected," scientists say

Environmental scientists have warned that the potential spread of COVID-19 via sewage "must not be neglected" since the viruses shed from the digestive system of infected individuals tend to last longer than those from the respiratory tract.

The research, published in the journal Environmental International, noted that while response to pandemic is focused on preventing person-to-person transmission, the virus might also spread in wastewater.

"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," said Richard Quilliam, study co-author from the University of Stirling in Scotland.

Based on their new findings, the scientists warned that the sewerage system itself may pose a transmission risk.

They said the structural makeup of SARS-CoV-2, 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 the study noted that other coronaviruses can remain viable in sewage for up to 14 days, depending on the environmental conditions.

"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," Qulliam said.

Hence he said the fecal-oral route could be an important -- but as yet unquantified -- pathway for increased exposure.

Quilliam said since most COVID-19 patients are asymptomatic or experience just mild symptoms and remain at home, there is significant risk of "widespread" distribution through sewers.

According to the biologists, lack of testing "makes it difficult" to predict the scale of the potential spread and the public health implications of the virus arriving at wastewater treatment works.

"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," the scientists wrote in the study.

According to the study, the risk of fecal-oral transmission could be further increased in parts of the world with high levels of open defecation, or where safely managed sanitation systems are limited.

In these places, the scientists said 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," the researchers noted.

Currently, all published data on faecal shedding of SARS-CoV-2 derive from hospitalised patients with limited information on mild and asymptomatic cases, they added.

"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," the study concluded.