Wastewater is now helping track measles spread around the US

(CNN) — As measles cases rise to precipitously high levels in the US this year, there’s a new tool to help track the spread: wastewater.

Wastewater surveillance rose to prominence during the Covid-19 pandemic, as testing sewage for virus particles helped provide early warning signs of increased transmission and fill the gaps as case reporting scaled back.

Now, WastewaterSCAN has developed the first national wastewater monitoring program to detect measles in places where people are infected with the virus. It has the potential to identify possible cases days before an individual shows symptoms or seeks care. The new tool is available for use in nearly 150 wastewater treatment facilities across 40 states.

At least 1,157 measles cases have been reported in the US this year, according to a CNN tally using data from state health departments.

A large multistate outbreak centered in West Texas accounts for the vast majority. Texas has reported 742 outbreak-associated cases, New Mexico reported 81 cases, and Oklahoma reported 18 cases – 15 confirmed and three probable – as of Tuesday. Cases in Kansas, which the state health department says may also be linked to the outbreak, have reached 71 as of Monday.

Experts say these numbers are all a severe undercount because many cases are going unreported. However, the nation is now fewer than 120 cases away from the total reported for all of 2019, the year with the highest number of measles cases – 1,274 - since the disease was declared eliminated in the US in 2000.

South Dakota reported its first measles case of the year Monday, bringing the total number of states that have reported at least one case in 2025 up to 33.

The new case in South Dakota is in an adult who travelled internationally, according to a news release from the state health department.

The US Centers for Disease Control and Prevention recently updated its measles guidance for travelers.

“Travelers can catch measles in many travel settings including travel hubs like airports and train stations, on public transportation like airplanes and trains, at tourist attractions, and at large, crowded events,” a CDC advisory says. “Infected travelers can bring the disease back to their home communities where it can spread rapidly among people who are not immune. CDC recommends that all travelers be fully vaccinated against measles before traveling to any international destination.”

Other recent examples include a case in Minnesota that was reported in an adult who was exposed during domestic air travel, and the New Jersey health department has warned of potential measles exposure in the Newark airport.

There have been at least 14 outbreaks in the US this year, according to the CDC, accounting for 90% of cases. The CDC’s data is limited to confirmed cases and lags behind CNN’s tally for this year.

The vast majority of cases in the US this year have been in people who are unvaccinated; only about 5% of confirmed cases have been in people who had received one or two doses of the measles-mumps-rubella (MMR) vaccine, according to the CDC.

Two doses of the MMR vaccine are 97% effective against measles. The CDC recommends two doses as the best protection against the disease, with the first dose given at 12 to 15 months of age and the second between ages 4 and 6.

Childhood vaccination rates have been declining across the US for years, with MMR vaccination coverage among kindergartners falling below the recommended 95% threshold for at least four years.

New research from Johns Hopkins University, published Monday in the journal JAMA, emphasizes how widespread the decline has been. MMR vaccination rates among children have dropped in more than three-quarters of US counties, with an average drop of 2.7% between 2017 and 2024, according to the study.

Vaccination rates have surged in some places that are experiencing measles outbreaks, however. In New Mexico, nearly twice as many MMR vaccines have been administered this year than there were at this point last year, according to data from the state health department. And a recent analysis of health records by Truveta, a health-care data and analytics company, shows that early vaccination rates jumped among infants in Texas. MMR vaccination rates among 6-month-olds in Texas this year are more than eight times higher than they were in 2019, and in March and April, about 1 in 5 children who received their first measles shot in Texas had gotten it early, before their first birthday.

At least 133 people with measles have been hospitalized this year, according to the CDC, and there have been three deaths: two children in Texas and one adult in New Mexico, all of whom were unvaccinated.

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