DENVER — An out-of-state traveler with measles could have exposed thousands of people at Denver’s Union Station and a hotel in Steamboat Springs earlier this week, state health officials said Friday.

The unvaccinated individual may have exposed people at Denver Union Station on Tuesday, Sept. 15, between 6 p.m. and 9 p.m., and hotel guests at the La Quinta Inn located at 3155 Ingles Lane in Steamboat Springs the following morning between 9 a.m. and 2:30 p.m., according to a spokesperson with the Colorado Department of Public Health and Environment.

Why measles outbreak in the US has reached 35-year high

Measles is a highly contagious viral infection that spreads through the air and can remain airborne for up to two hours — meaning people may have been exposed even if they were nowhere near the infected person at the time.

State health officials said those who were potentially exposed to the virus may develop symptoms through Tuesday, Oct. 6 and Wednesday, Oct. 7, respectively.

Anyone who believes they may have been exposed — especially those who have not been vaccinated with the MMR vaccine — should monitor for symptoms for 21 days and avoid public gatherings or high-risk settings, health officials said in a news release.

Symptoms to watch out for include anything from a fever, a cough, a runny nose, and red, watery eyes that develop into a rash that starts on the face and then spreads to the rest of the body about three to five days after symptoms first start. A person with measles is contagious four days before and four days after the rash appears.

State health official surge people who develop symptoms to call the CDPHE at 720-653-3369 or their local public health agency immediately by phone before trying to seek treatment to avoid other people from becoming potentially infected with the virus. The CDPHE urges people to call an urgent care center or emergency department and explain that you may have been exposed to measles if you do not have a health care provider.

While most people recover within two or three weeks after contracting the virus, unvaccinated people run the risk of complications from the disease, including ear infections, seizures, pneumonia, immune amnesia, brain damage and ultimately, death.

• Denver7 has been closely following confirmed measles cases in Colorado amid a multi-state outbreak in the U.S. that began last year. Explore the map by clicking here or check it out below to see where cases have popped up in 2026:

Measles only spreads from people who show symptoms; it does not spread from people who aren’t feeling sick, state health officials said.

Unvaccinated people exposed to the virus can get the MMR vaccine 72 hours after exposure (but before symptoms are present) to prevent an infection, according to health officials. If vaccination is not possible, antibody treatment can help in some cases if it’s given within six days of exposure, state health officials said.

“Getting vaccinated is the best way to protect yourself, your family, and your community,” the CDPHE spokesperson said.

While the two-dose series of the MMR vaccine has a 97% efficacy rate against infection, about 3 in every 100 people can still get infected if exposed to the virus for a prolonged period of time, according to the U.S. Centers for Disease Control and Prevention. Vaccinated individuals will usually develop milder symptoms and are less likely to spread it to others, according to state health officials.

People who got vaccinated against measles before 1968 should talk to their health care provider about possibly getting a booster as the vaccine used before that year wasn't as effective.

Colorado experienced a reprieve in measles activity this summer following several outbreaks in the northeastern part of the state at the beginning of the year, but the highly contagious disease started making headlines again after the CDPHE announced an international visitor who was later confirmed to have measles traveled to areas northwest of Denver last week.

As of Friday, Colorado had reported 25 cases of the virus across 8 counties: Adams (5), Arapahoe (1), Broomfield (5), Delta (1), Lake (6), Larimer (1), Saguache (1), and Weld (5), according to statewide data. For context, that's about 69% of all cases the state reported all of last year. Up until 2014, Colorado saw between zero and two cases each year.

Across the nation, the number of confirmed measles infections this year has so far reached 3,471 — numbers not seen in 35 years, according to CDC data — with the majority of cases happening among unvaccinated children.

At least four measles-related deaths have been reported across the U.S. so far in 2026. The last time the U.S. reported four measles deaths was 34 years ago, in 1992.