How can testing sewage reveal an outbreak before hospitals do?
Poliovirus was tracked through the sewage of New York and Chicago in the 1940s, and the same idea now tracks COVID and mpox.
Sewage can reveal an outbreak because many viruses are excreted in feces, and a treatment plant collects the waste of a whole community in one place. Scientists sample the wastewater, measure the genetic traces of a germ, and learn about the whole population at once, including people who never get tested, so a rise can give health departments lead time before the patients arrive. The method is called wastewater-based epidemiology, and it works like urinalysis on a community scale: its results are population-level rather than individual level.
It is not a new idea. In the 1940s the technique was applied to detect and track poliovirus in the sewage of New York, Chicago and other cities, and the WHO today recognises wastewater testing as an important tool for polio surveillance, especially where mainstream surveillance methods are lacking. During the COVID-19 pandemic it was used in various countries as a complementary way to assess the load of the virus and its variants in populations, and it was used to detect monkeypox in the 2022 outbreak.
Step 1: Flush
Infected people shed germs and traces
Step 2: Treatment plant inlet
Waste of the whole arrives
Step 3: Autosampler
A 24-hour sample is collected before treatment
Step 4: Lab
PCR or sequencing measures the traces
Step 5: Health department
Trends give lead time to decide
The big advantage is time and scope. A warning from wastewater can give health departments critical lead time, and unlike testing individuals, it covers the entire population in a area. The limits are real too: it is unclear how cost-effective it is, and less common infections may be difficult to detect.
1940s
Poliovirus tracked in sewage of New York and Chicago
2013
Study finds Aichivirus A in Dutch sewage from 1987
2022
Used to detect monkeypox; global antimicrobial-resistance survey
Quiz me
0/3
Recap
Test the sewage at the treatment plant and you test the whole catchment at once, which can give an early warning but cannot catch everything.
💡 A trick to remember it · A city's sewer is its shared diary: every flush adds a line, and the lab reads the whole page at once.
Surprising fact · In the 1940s, poliovirus was already being tracked in the sewage of New York and Chicago.
Connects to
- 🧪 How do PCR and rapid antigen tests tell whether you are infected?
- 🧫 How many people die from drug-resistant infections, and how did the 2019 Lancet study count them?
- ♨️ How did a microbe from a Yellowstone hot spring make PCR possible?
- 🚰 How did London's sewers defeat cholera for the wrong reason?
- 🦠 How do bacteria become resistant to antibiotics?
Sources (1)
No source, no claim. Every fact in this lesson (15 claims) cites at least one of these.