A case of measles has been confirmed in DeKalb County and health officials tracked probable recent exposure to Walmart and the post office in DeKalb, the DeKalb County Health Department reported Thursday.

Health officials said in a news release that the first local case of 2026 was confirmed through laboratory testing.

Symptoms to monitor after possible exposure

Anyone who isn’t vaccinated against measles and was inside the Walmart, 2300 Sycamore Road in DeKalb, from 2:30 to 4:45 p.m. on March 2 should monitor themselves until March 23 for symptoms of the viral disease, according to the health department’s news release.

Unvaccinated people who were inside the DeKalb Post Office, 600 E. Lincoln Highway, from 6 to 8:30 p.m. on March 9 should also monitor themselves for symptoms until March 30, officials reported.

Symptoms such as a rash, high fever, cough, runny nose and red, watery eyes could indicate a measles infection, according to the news release.

Health Department officials are asking that anyone who was exposed, or who develops a rash and one other symptom, contact them by long-distance communication.

“Call or email your healthcare provider BEFORE (sic) visiting a clinic or hospital so staff can take steps to prevent the illness from spreading to others,” health department officials wrote. “The MMR vaccine is the best protection against measles. DCHD encourages everyone to make sure they are up to date on their MMR vaccinations.”

Vaccine prevention

Measles is considered the most contagious vaccine-preventable disease in the world. Most people are protected from measles through two doses of the MMR vaccine, however.

That vaccine, which also protects against mumps and rubella, is considered about 97% effective at preventing measles. That efficacy stymies the spread of the disease by limiting the number of people who can host the virus.

Not everyone is vaccinated, however.

Babies and infants too young to receive the vaccine are considered among the most at risk of developing the disease, according to the DeKalb County Health Department.

As of March 5, before the first case of measles in DeKalb County in 2026 was confirmed, the U.S Centers for Disease Control and Prevention reported two measles cases in Illinois for the year. Fourteen cases were reported in Illinois during all of 2025 and 67 in 2024.

Illinois has bucked a recent national trend, however. Weekly confirmed measles cases in the U.S. increased from an average in the single digits in 2022, 2023 and much of 2024, according to CDC data. That data shows the last time fewer than 11 measles cases were reported in the U.S. was the week of Jan. 12, 2025.

In 2025, the CDC confirmed 2,283 measles cases. More than half that total, 1281 measles cases, were confirmed by the CDC in 2026 as of March 5.