New Mexico wastewater testing for measles last year forewarned public health experts of the spread to a new county five days before cases were clinically confirmed during the state’s outbreak, according to a new study.
The study, authored by Kelley Plymesser, the head of water-based epidemiology at the New Mexico Department of Health, in collaboration with federal health officials and researchers at Rice University, demonstrates a method for early warning about measles even before people seek medical care. While testing sewage rose to prominence in 2020 during the COVID-19 pandemic, New Mexico public health officials last year expanded surveillance to include measles.
“It did exactly what it was supposed to do, it gave us an early-warning system, particularly in areas where there were no reported cases yet,” Plymesser told Source NM.
Last year, between February and September, New Mexico reported its first measles outbreak since 1996. All but one of New Mexico’s 100 measles infections stemmed from cases in neighboring West Texas counties that ultimately spilled over into 31 states and remains ongoing in several of them.
Between March and August of 2025, health officials collected samples weekly of untreated wastewater from nine treatment plants across six counties: Bernalillo, Chaves, Doña Ana, Luna, Sandoval and Santa Fe. The Stadler Laboratory at Rice University tested the samples and returned the results to NMDOH within 10 days.
A “very surprising result” came in May of 2025, Plymesser said, when Sandoval County wastewater tested positive, despite no reported cases and no neighboring counties with cases. Five days later, hospitals confirmed several cases.
Measles can spread in the days before and after symptoms appear, so the positive results found in sewage allowed health officials to prepare additional vaccines and put providers on the lookout, Plymesser said.
“That five-day window gave us a few days to plan and mobilize and send out our measles outbreak response team, alert the providers, give us more time to prepare,” she said.
Plymesser said the findings are important because measles, a highly contagious airborne virus, continues to spread across the country, with the U.S. experiencing its largest measles outbreak in decades. Experts this month wrote in the medical journal Lancet that the disease’s ongoing spread threatens the country’s “eradication” of the virus declared by the Centers for Disease Control and Prevention in 2000, following decades of nationwide vaccination efforts.
In New Mexico, health officials have thus far reported 15 cases of measles in 2026, all contained to federal detention centers. No new New Mexico cases have been reported since March.
Wastewater testing does have some limits, Plymesser said, noting that 30% of the state’s residents use septic tanks, which NMDOH cannot test. Additionally, wastewater testing can only identify ongoing spread, but cannot pinpoint individual cases.
Plymesser said NMDOH expects to use the tool for the foreseeable future, as the CDC has funded the program through 2027 and the grant extends to 2029.
“We are continuing to use wastewater surveillance and continuing to broaden the scope of what we’re looking for,” Plymesser said.
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