Tempe, Arizona, has been trying to use sewage to prevent coronavirus outbreaks.
“Wastewater is a lead indicator [of a virus outbreak], while people testing positive is a lag indicator,” said Rosa Inchausti, director of strategic management and diversity for the city of Tempe. “Wastewater is a lead indicator because people shed the virus up to seven days prior to showing symptoms.”
By testing wastewater, officials in Tempe were able to quarantine people in “Area 6” of the city who were infected with the virus. According to Inchausti, the residents in Area 6 are some of the poorest in Tempe. Many are immigrants. It is not uncommon for multiple generations to live under one roof, making quarantining difficult. For people in such households who are sick with COVID-19, the city was able to place them in a local motel to quarantine.
“No one’s traveling and using hotels,” said Inchausti. “It was a great way to use resources and partner with the business community.”
Individuals excrete the virus through feces, so testing sewage can inform officials when more people are being infected before they are likely to show up at the hospital. The more targeted the testing, the more focused public health efforts can be. Tempe is able to identify concentrations of the virus by testing the wastewater in seven different areas three times a week.
Area 6 of Tempe is a small area in the center of the city adjacent to Arizona State University. In early September, it started showing high amounts of the coronavirus in the wastewater. Authorities began offering saliva-based testing for the virus through the schools in Area 6 and hand-delivering masks to homes and businesses. The city also partnered with nonprofit groups to do outreach and to educate residents about proper safety protocols. This enabled officials to identify infected people who were living in crowded conditions and to isolate them.
The amount of the coronavirus in the wastewater in Area 6 has dropped since mid-October.
“We did see the numbers come down, although we can’t say that has all been because of this deployment of services,” said Inchausti.
Tempe conducts its own testing, but many cities take samples and send them to companies that then test them for the coronavirus. Biobot is one of the largest of those companies. Jennings Heussner, a business development associate at Biobot, said the company has over 450 customers for coronavirus testing.
“We work with cities and states, colleges and universities, and businesses, including some Fortune 500 companies at their corporate campuses,” Heussner said. “It’s a diverse set of customers.”
A research paper from Biobot suggests that wastewater testing can find people who are infected while they are still asymptomatic. It found that increased viral loads appeared in wastewater four to 10 days prior to an increase in cases found via individual testing.
Not all cities that engage in testing wastewater are as far along as Tempe. Sacramento only tests its water once a week and only at the sewage treatment plant.
“It’s not cheap, so the more sample sites you go to and analyze, the more it costs,” said Christoph Dobson, director of policy and planning at the Sacramento Area Sewer District. “We have thought about [sampling more sites], but it has to be in the context of what is the benefit of that information and how much does it cost?”
Inchausti said she is bullish on the potential of testing wastewater to stem the pandemic.
“I think this is a game changer for public health. … I think this is how cities should be managed,” she said. “The power in this is knowing where the virus is before people are showing symptoms or being tested. So, the asymptomatic is where we need to focus.”
But Heather Bischel, a professor of civil and environmental engineering at the University of California at Davis, said she thinks it is just one of many useful tools.
“I think it can be a useful, complementary tool to a lot of other things that are going on,” Bischel said. “This isn’t going to save the day for everyone. But in areas where individual testing is poor, this could be very helpful.”
