(NEXSTAR) – A total of 800 measles cases across two dozen states have been confirmed, the Centers for Disease Control and Prevention says.

As new cases pop up every week, at least 10 official outbreaks have occurred, according to the CDC. An outbreak is defined as three or more cases of measles that are related.

The largest known outbreak is in West Texas, where the case count nears 600, according to local health officials.

The CDC said it’s still investigating other probable measles cases that have been reported but not yet confirmed. Montana, for example, announced Friday the state has seen measles crop up for the first time since 1990.

The map below shows which states have measles cases confirmed by the CDC. States shown in red have a confirmed measles outbreak of three or more cases.

Another outbreak not shown in the map above is being investigated, a CDC spokesperson told Nexstar. The agency isn’t yet releasing the location of the outbreak to protect patient privacy as officials investigate.

If the spread of measles continues as it has been, the U.S. risks losing its “measles elimination status,” a designation the country has had for 25 years.

The highly contagious virus is spreading quickest through communities with large numbers of unvaccinated or undervaccinated people. Dr. William Moss, an epidemiology professor at the Johns Hopkins Bloomberg School of Public Health and director of the school’s International Vaccine Access Center, likened recent measles activity to a forest fire.

“I like to think of this like a forest fire with sparks spreading out. If those sparks land in a community with low vaccine coverage, we’re going to see a larger measles outbreak. If it lands in a community with high vaccine coverage, we may only see one or a few cases,” he said.

The CDC reports 96% of cases so far have been in people who are unvaccinated or whose vaccination status is unknown. The majority of those sickened have also been children.