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What can wastewater tell us about covid-19?

Testing sewage and wastewater has been an effective mechanism to track the spread of the virus. Stanford researchers have now devised a method that also tracks whether infection rates are trending up or down

City of San José Environmental Services Department's environmental inspectors Isaac Tam and Laila Mufty deploy an autosampler into a manhole at the San José - Santa Clara Regional Wastewater Facility. (Photo credit: City of San José Environmental Services Department)

Earlier this year, scientists in Italy revealed that sewage water from two cities -- Turin and Milan -- contained traces of the novel coronavirus in December 2019. This was long before the European country recorded its first confirmed cases in the middle of February. Researchers from the National Institute of Health in Italy said water from these two cities showed genetic virus traces on 18 December, a BBC report noted.

Similarly, a study in Spain had found traces of the virus in waste water collected in Barcelona in mid-January, around 40 days before the first local case was discovered, the BBC report from June added.

The testing of sewage and wastewater has proven to be an effective mechanism to understand the spread of the virus that causes covid-19. Now, in a new study, researchers at Stanford University have identified a method that not only detects the virus in solid wastewater samples but also tracks whether the infection rates are trending up or down.

This test identifies and measures genetic material in the form of ribonucleic acid, or RNA, from SARS-CoV-2, the virus that causes covid-19. “This work confirms that trends in concentrations of SARS-CoV-2 RNA in wastewater tracks with trends of new covid-19 infections in the community. Wastewater data complements the data from clinical testing and may provide additional insight into covid-19 infections within communities,” said Alexandria Boehm, a Stanford professor of civil and environmental engineering, and co-senior author of the study which was published in the Environmental Science & Technology journal on 7 December.

Detecting covid-19 can be particularly tricky especially in case of asymptomatic or mild cases. But research has shown that wastewater can be a robust source to test covid-19 in community settings as infected individuals shed the virus in their stool or feces. This method can also prove useful in alerting decision-makers and healthcare officials about potential outbreaks days before individuals start noticing symptoms. “Anyone with a toilet connected to a sewer system could be depositing these biological samples on a regular basis, making wastewater sampling an inclusive source of information about covid-19 in a community,” an official news release from Stanford University explains.

To improve the effectiveness and accuracy of wastewater testing further, the researchers at Stanford compared the ability to detect the virus in two forms of wastewater - a mostly liquid influent or settled solids (sediment settled in a tank). While most research currently in this area focuses on influent samples, the team noted that many viruses have an affinity for solids and expected higher concentrations of the virus in such samples. The researchers tested about 100 settled solid samples from the San Jose-Santa Clara Regional Wastewater Facility from mid-March to mid-July this year. They found that the solids contained 100-1,000 times higher concentrations of SARS-CoV-2 genes than the wastewater influent on a per mass basis.

There’s still plenty of information that needs to be collected to understand the limitations of testing wastewater, including the virus’ rate of decay in wastewater, the extent and timeline of viral RNA shedding when someone is sick

They even tallied daily concentration numbers and using statistical modeling compared these concentrations with confirmed covid-19 cases provided by the county. “Their results tracked the trend of the county's cases, decreasing in both May and June and peaking in July,” the news release explains. The researchers believe these findings and the new testing method could help identify potential outbreaks and even find hotspots. The technology could also be implemented in schools, as they prepare to reopen, to understand if community transmission is decreasing. Similarly, this method could also be useful in areas, which lack the resources for proper clinical testing.

As the release explains, there’s still plenty of information that needs to be collected to understand the limitations of testing wastewater, including the virus’ rate of decay in wastewater, the extent and timeline of viral RNA shedding when someone is sick. In the past, scientists have used wastewater to test for everything from narcotics usage to antibiotics resistance. This new-found option to test for the spread of the novel coronavirus presents a somewhat unconventional but useful response to the pandemic.

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