Researchers around the world have been surveying our sewage in the hopes of tracking SARS-CoV-2 infections. In two separate studies, scientists from the Ben-Gurion University of the Negev (BGU) in Israel, and environmental biologists at the University of Stirling in the UK, warn that the sewerage system itself could pose a transmission risk for SARS-CoV-2, the virus that causes Covid-19.
Researchers from BGU developed a new methodology to trace SARS-CoV-2 through the sewage and wastewater systems, which could potentially be used to track existing and future outbreaks of the new coronavirus.
The new coronavirus has infected more than 4.1 million people and caused over 280 000 deaths worldwide, according to the Johns Hopkins Coronavirus Resource Centre. On the bright side, however, scientists are looking into wastewater as a tool to monitor the virus. In countries with limited resources, this means of surveillance could be the key to finding out what geographic areas have higher numbers of people infected with the virus.
The preliminary study by BGU researchers involved sampling at wastewater treatment plants in Israel before, during and after the Covid-19 outbreak. They found that if clinical testing is deficient in determining the infection rate of the new coronavirus using the population size, environmental monitoring of sewage may come in handy and provide effective estimates of the prevalence of the virus in certain geographical locations.
This is especially relevant, considering that up to 80% of infections are mild or asymptomatic (showing no symptoms), indicates a World Health Organization (WHO) report, published in March. However, while the research team determined that the virus is indeed transferred via faeces into sewage, they are still trying to determine whether the virus found in sewage remains viable and is able to infect humans.
Similarly, after an analysis of sewage in the UK, the research team at the University of Stirling warned that the sewerage system itself could pose a transmission risk and "must not be neglected".
Professor Richard Quilliam's new paper, published last week in Environmental International, calls 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. 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."
- There could be an increased risk in parts of the world with high levels of open defecation; in places with limited safely managed sanitation, and waterways that serve as open sewers, as well as a source of water for domestic use. "Such settings are commonly accompanied by poorly resourced and fragile healthcare systems, thus amplifying both exposure risk and potential mortality."
WHO notes that only 45% of the global population uses a safely managed sanitation system and at least 10% is thought to consume food irrigated by wastewater.
The researchers are therefore calling for investment in further research so that there can be a clearer understanding of the risks associated with faecal transmission of this new virus.
"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,” they explain.
Wastewater is already used to detect polio, a highly infectious viral disease that mainly affects children under the age of five. The virus particles are shed in the faeces, and WHO encourages countries to exploit the use of existing sewage sample collection systems whenever possible.