How wastewater could offer an early warning system for measles
Measles is back with a vengeance. In the UK, where only 85% of school-age children have received two doses of the MMR vaccine, as many as 300 people have contracted the disease since October. And in the US, an outbreak has infected nine people in Philadelphia since last month. One case has been reported in Atlanta, another in Delaware. An entire family of six is infected in Washington state.
On January 23, the World Health Organization issued a warning. It is vital that all countries are prepared to rapidly detect and timely respond to measles outbreaks, which could endanger progress towards measles elimination," said Hans Kluge, WHO regional director for Europe.
Catching measles outbreaks early is tricky, though. Like many other respiratory viruses, it starts off with a cough, runny nose, fever, and achy body. The telltale rash doesn't appear for two to four more days. By then, a person is already infectious. Very infectious, in fact. Measles is one of the most contagious diseases around.
Maybe there's a solution. The US developed a vast wastewater sampling network to detect covid during the pandemic. Could we leverage that network to provide an early warning system for measles?
I actually think you could make the argument that measles is even more important to [detect] than covid or influenza or any of the other pathogens that we're looking for," says Samuel Scarpino, an epidemiologist at Northeastern University in Boston.
Wastewater surveillance relies on standard lab tests to find genetic evidence of pathogens in sewage-DNA or RNA. When people are infected with covid, they shed SARS-CoV-2 in their stools, so it's easy to see why it would show up in wastewater. But even viruses that don't get pooped out can show up in the sewers.
Although measles is a respiratory virus, people shed it in their urine. They also brush their teeth and spit in the sink. They blow their noses and throw the tissue in the toilet. We shed these viruses and we shed bacteria and fungi in so many ways that end up in the sewer," says Marlene Wolfe, an environmental microbiologist and epidemiologist at Emory University and one of the directors of WastewaterSCAN, a program based at Stanford that monitors infectious diseases through municipal wastewater systems.
The literature on wastewater detection of measles is scant, but encouraging. In one study, a team of researchers in the Netherlands tested wastewater samples collected in 2013 during a measles outbreak in an orthodox Protestant community for evidence of the virus. They found measles RNA, and the positive samples matched the locations where cases had been reported. They even managed to confirm that the virus in one sample was genetically identical to the outbreak strain. But not every measles case showed up in the sewers. Some samples taken where cases had occurred didn't harbor any measles RNA.
In another study, researchers from Nova Scotia developed a tool to screen wastewater for four pathogens simultaneously: RSV, influenza, covid, and measles. When they tested it in Nova Scotia, they didn't get any positive hits for measles, which didn't surprise them as no cases had been reported. But when they seeded the wastewater samples with a surrogate for measles, they were able to detect it at both high and low concentrations
The real question, Wolfe says, is whether detecting measles in wastewater would have any public health value. Because measles is rarely asymptomatic and the rash is so distinctive, cases tend to get noticed. Some of our other systems can work pretty well at identifying measles cases as they come up," she says.
Wolfe could see value in monitoring, she says, if people really shed high quantities of the virus before those signs are visible. Then it really could provide an early warning," she says. But that's not known at the moment.
What would a wastewater surveillance program for measles look like? If we had the ability to target places where the vaccination coverage was lower, that would be a place to prioritize resources," Scarpino says. Airports and other ports of entry are going to be really important as well." Earlier this month, someone infected with measles passed through both Dulles and Ronald Reagan airports just outside of Washington, DC. Finding measles RNA in airport sewage doesn't necessarily mean a local outbreak might occur, but it definitely means that the risk profile is there and we should be monitoring much more actively," he says.
While measles isn't part of wastewater surveillance yet, plenty of other pathogens are. Health officials around the globe have been testing sewage for polio since the late 1980s. Because people who contract polio shed large amounts of the virus in their feces, and because so many people are asymptomatic, it's like a perfect use case in a lot of ways," Wolfe says. But wastewater surveillance didn't really become fashionable until 2020, when covid hit.
The National Wastewater Surveillance System, which the Centers for Disease Control and Prevention (CDC) launched in 2020 to monitor covid, now also tests for mpox. WastewaterSCAN currently tests for 10 different pathogens, including covid, mpox, RSV, influenza, norovirus, and rotavirus. The team publishes that data on a dashboard on its website and shares it with the CDC. Wolfe and her colleagues also recently worked with Miami-Dade County in Florida to assess the feasibility of testing for dengue. Even though dengue is rare in Florida, the team picked up a signal in the wastewater.
In fact, wastewater surveillance works for most of the pathogens they've tried, Wolfe says: The potential for leveraging this tool to effectively support measles surveillance is absolutely possible."
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Read more from MIT Technology Review's archive
Wastewater with its wealth of microbes could help researchers track the evolution of antibiotic resistance in bacteria, Jessica Hamzelou wrote last year.
Health officials used wastewater surveillance to track the spread of mpox in 2022 and helped scientists estimate how many people in California's Bay Area might be affected, Hana Kiros reported.
Way back in 2021, Antonio Regalado covered some of the first efforts to track the spread of covid variants using wastewater.
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