Public health officials have confirmed a measles case in Boulder County.

The child was not vaccinated against measles, mumps and rubella and had not traveled outside the state or had a known exposure, according to state health officials.

The case brings the total number of measles infections in Colorado to two.

“The lack of a clear source of infection suggests that unidentified measles cases may be occurring in or traveling through the area,” state officials said Friday.

The other case was in Arapahoe County.

Dr. Michelle Barron, senior medical director of infection prevention and control for UCHealth, has warned about the risk of out-of-state travelers who may be unvaccinated.

“Colorado’s big risk right now is it being imported from somebody visiting,” Barron said.

Last year, Colorado had 36 cases, with roughly one in four associated with an out-of-state traveler who flew while infectious, according to the Colorado Department of Public Health and Environment.

That was more cases than Colorado had over the past decade.

Measles had been thought to be a thing of the past. The disease was considered eradicated in 2000, which health officials credited to a highly effective vaccination campaign.

Before a vaccine was developed, an estimated 48,000 Americans were hospitalized with measles each year and 500 died.

Measles is a highly contagious and preventative respiratory illness. The disease is transmitted through direct contact with infected droplets or airborne when an individual breathes, coughs or sneezes.

Symptoms typically emerge within two weeks of exposure. The telltale sign of a measles infection is a spotty red rash. In rare cases, measles can cause swelling of the brain and death.

About 93.3% of students in Colorado were vaccinated for measles, mumps and rubella, state vaccination records show. To be protective in a community, 95% or more students should be vaccinated against measles.

The positive cases in Colorado come as the United States has seen an unprecedented rise in the number of cases.

As of Feb. 20, there have been nearly 1,000 confirmed measles cases in 26 states with roughly 90% associated with an outbreak, according to the Centers for Disease Control and Prevention.