Wastewater testing has picked up rising levels of COVID and even evidence of polio. Can it predict new viral outbreaks?
Yogi Berra said it well: “It’s hard to make predictions, especially about the future.”
Although he wasn’t talking about viral infections or the current pandemic, he might as well have been. Even the best scientists, infectious disease specialists, and epidemiologists have found it difficult to accurately predict when new viral outbreaks will emerge (think COVID-19), when old ones will reemerge (think polio), and how understand this in time to make a difference. But what if they could? An already available tool called wastewater testing shows promise — and how we use the results could help stem the future surge of COVID or predict the rise of a surprising new virus.
COVID: When can we expect the next increase?
For months, the US has recorded over 100,000 new cases of COVID-19 and 300 deaths every day. And in fact, the number of cases is probably much higher because testing rates have fallen and positive tests at home are not included in official counts. With numbers like these and new variants emerging, further increases in cases seem inevitable.
But when?
Perhaps in the coming weeks as new and highly contagious variants spread. Or maybe in the fall and winter, since we spend more time indoors. Or maybe this virus will surprise us again and wait until next year to revive.
A major challenge in containing the COVID-19 pandemic is that by the time we know infections are rising rapidly in a community, it has already been going on for some time. Because people often have no symptoms at first, the infection can spread for a while without warning.
If we could predict when the next surge will occur, it is possible to take appropriate preventive measures. And that’s where your poop comes in—poop, excrement, whatever you prefer to call it.
Detection of viral outbreaks using wastewater
The idea is simple: when people have a viral infection, the virus can often be detected in their stool. Therefore, sewage from a town or city, or perhaps a community, can be tested to see if the virus is present and, if so, if the amount is increasing over time.
This approach has been used since the 1940s, when polio was a major concern. But sewage tests can also be used to detect some types of hepatitis, the flu-like norovirus and possibly measles.
The methods used to test wastewater have improved over time. Early efforts attempted to grow viruses from water samples; more recently, testing has moved toward detecting viral genetic material.
Polio and COVID in sewage
In June 2022, sewage testing in London revealed the virus that causes polio, a potentially life-threatening or disabling disease. Although no active cases of polio have yet been diagnosed in London, the discovery prompted an investigation into where the virus originated, who might be infected and whether there is any threat to public health.
In the US, a county in New York that had been testing wastewater for levels of COVID also began testing for polio after an active case of polio occurred in an unvaccinated adult.
Has wastewater testing proven useful to detect and track SARS CoV2, the virus that causes COVID-19? Actually, there is. Levels of this virus in sewage have closely mirrored infection rates in many cities around the world, and in some cases predicted an outbreak before a community even noticed cases were rising. The CDC now includes wastewater data in its regular reporting of COVID-19 infection rates.
The results of wastewater testing are usually combined with other information, such as infection rates reported by hospitals and doctors’ offices, infection trends in nearby communities, and vaccination rates. Together, this information provides public health officials with better information about a variety of worrisome viral infections and where to target case numbers.
How is wastewater data useful?
Detecting the presence or an increased level of the virus in wastewater can help public health officials, health care providers and researchers
- predict when a surge is occurring or peaking
- update messages about prevention measures (for example, advice to wear a mask in public spaces or to physically distance)
- demand more vaccines and antiviral drugs
- encourage more testing
- identify new variants.
Letting people know if cases are increasing in their community can be especially important for those who face barriers to testing, including people who don’t have health insurance or a primary care physician. Wastewater testing can be particularly useful when undercounting is common, as in the case of COVID-19.
In the future, wastewater testing may be improved to the point where we can narrow down the site of an outbreak to a single neighborhood, or a residential facility such as a nursing home or prison.
After all
Unfortunately, the COVID-19 pandemic is not over. And we are hearing alarming reports of the international spread of the virus that causes monkeypox. In the future, it is very likely that old viruses such as polio and measles will re-emerge and new pandemics will spread.
We’re going to need all the help we can get to stay ahead of these outbreaks. Some of this help is likely to come from wastewater. So, as strange as it may seem, what you flush down the toilet can help health officials detect — and possibly contain — a public health threat.
Follow me on Twitter @RobShmerling
