Measles cases in the U.S. have been rare in recent decades, thanks to a strong childhood vaccination program. But a few cases inevitably pop up each year as travelers bring the virus in from other countries and infect unvaccinated people, primarily children.
Those cases are no longer blips. Now that the measles vaccination rate is dropping precipitously across the U.S.—due in part to anti-vaccine sentiments—cases are rising. So far in 2025, 14 outbreaks have been reported in 33 states, according to the U.S. Centers for Disease Control and Prevention (CDC). (By comparison, in 2024, there were just 16 outbreaks reported during the entire year.)
Scientists may now have a new way to catch cases. For the first time, researchers have posted national information on where the measles virus is showing up in wastewater.
Wastewater surveillance is a useful public-health tool because it provides an objective glimpse into where a given virus is causing infections—often before traditional testing methods. For viruses like measles, which infected people shed in urine, feces, or saliva, it can provide a critical heads-up for health officials. “It gives us a finger-to-the-wind weather map of what is happening with infectious diseases,” says Dr. Marlene Wolfe, assistant professor at Emory and principal investigator and co-program director of WastewaterSCAN, an academic and commercial group that includes researchers from Stanford University, Emory University, and Verily (which is Alphabet Inc.’s research organization).
Here’s what wastewater is revealing about measles in the U.S.
Adding measles to the menu of wastewater tests
WastewaterSCAN began testing sewage in the U.S. for the COVID-19 virus in 2020 and has since added other disease-causing microbes including influenza, RSV, human metapneumovirus (HMPV), norovirus, enterovirus, mpox, Candida auris, and hepatitis A.
This spring, the scientists began developing a test for picking up signs of the active or “wild type” measles virus that is causing outbreaks in the U.S. The test uses samples from nearly 150 sewage sites across the country and can pick up signs of measles within 48 hours.
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So far, they have detected it in three sites: one day in Hollywood, Md.; four days toward the end of May in Sacramento; and twice in mid-May in Stamford, Conn. WastewaterSCAN is only one such wastewater surveillance network in the country, though it’s the first to test for measles on a national level. The CDC launched its National Wastewater Surveillance System in 2020 and includes more than 1,400 sites that cover 150 million Americans. Some state health departments—including in Texas, where the current measles outbreaks began—also test wastewater samples. WastewaterSCAN collaborates with the CDC, but the CDC does not yet test for measles in wastewater.
Why wastewater monitoring may be especially useful for measles
Doctors who see patients with measles must report the case to the CDC so the agency can track it and respond to any outbreaks. But it takes time for people to develop symptoms, seek medical care, get tested, and then have their case reported if the test is positive. In addition, the first symptoms of measles are common ones like fever, runny nose, and cough—before the telltale rash appears. Plus, not everyone may get sick enough to know they have measles, so their cases may go unreported. Still others may get sick but not have access to health care and therefore never seek medical help.
Read More: Measles Vaccination Rates Are Plummeting Across the U.S.
Wastewater monitoring bypasses those hurdles and can theoretically catch evidence of the virus much earlier. That could be especially helpful with a highly contagious disease like measles, in which one infected person can quickly spread the virus to as many as 18 others. “This is anonymous testing that combines everyone in a community,” says Wolfe. “And for measles, it’s likely that shedding [of the virus] into wastewater is happening before people necessarily recognize what they have.”
How wastewater data can help health officials
This type of tracking for measles is too new to know yet whether it can detect cases in a region before people start testing positive, Wolfe says. But wastewater surveillance was able to pick up signs of the COVID-19 virus days or sometimes even weeks before cases began appearing in hospitals and testing labs.
Over time, as more data are collected on measles, health experts can begin to look for trends and patterns, such as increases in the number of positive samples. That could help public-health departments focus resources like vaccines in areas where infections are spreading. If the number of positive samples start to decline, that information could also give them a heads up when infections are under control.
What to do if cases are detected near you
Getting vaccinated is the best way to protect yourself against measles infection, and the immunization provides close to lifelong immunity. Making sure that anyone who is eligible is up to date on their measles vaccines can help them avoid infection.
