NEWS FEATURE
17 April 2024

What toilets can reveal about COVID, cancer and other health threats

Wastewater testing grew tremendously during the pandemic. But is it ready to tackle the opioid crisis, air pollution and antibiotic resistance?

By Betsy Ladyzhets

In late 2020, COVID-19’s global death toll was rising as cold weather in the Northern Hemisphere and holiday gatherings spurred rapid transmission of SARS-CoV-2 in the absence of a vaccine. Scientists and public-health officials were desperate for new ways to track the virus, which often moved faster than contact tracers could follow it.

Tong Zhang, an environmental engineer and microbiologist at the University of Hong Kong (HKU), and his colleagues were pioneers of what was fast becoming a popular surveillance method. They had been collecting periodic wastewater samples from about two dozen maintenance holes in the city and testing the sewage for coronavirus DNA, with support from Hong Kong’s government. In late December, they traced an outbreak to a single apartment building where there had been no sign of cases1.

The government quickly took action. Officials tested all of the building’s 2,000-odd residents; 9 tested positive. “Those people were isolated and went to a quarantine site. So they stopped the transmission chain,” Zhang says. After that success, he and his colleagues expanded their efforts.


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Wastewater testing remains part of Hong Kong’s COVID-19 strategy to this day. Zhang’s team tests for the coronavirus at about 20 sites across the city each week, he says, and the team has expanded the analysis of these samples to cover other pathogens, including influenza, rotavirus, norovirus and mpox, as well as markers of antimicrobial resistance. He views wastewater testing as a way to gauge the health of an entire community at once. “If we can make the methodology more standardized”, this tool becomes a “promising and exciting” way to screen the world for pathogens, including those that scientists haven’t yet identified,he says.

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