That person, an adult whose vaccination history isn’t yet known, hadn’t left Colorado and didn’t cross paths with either of the other two patients, meaning the state may have measles cases spreading undetected, state epidemiologist Dr. Rachel Herlihy said.

Colorado health officials warned Tuesday that measles may be spreading undetected in Colorado following the confirmation of the state’s third case this year in an Archuleta County resident. The Colorado Department of Public Health and Environment’s warning comes after two previous measles cases in Pueblo and Denver.

A third confirmed measles case in Colorado, this time in Archuleta County, is prompting renewed public health worries amid signs of potential community spread. The other two cases — a deli worker in Pueblo and an infant in Denver — do not appear to be related to the case in Pagosa Springs,