Is the Northern Arizona measles outbreak finally petering out?

Entering its fourth month, the measles outbreak along the Arizona-Utah border has reached nearly 230 cases. The outbreak will eventually burn out, but it’s unclear how long that will take. 

Beginning in August in the twin towns of Colorado City, Arizona, and Hildale, Utah — collectively known as Short Creek — the disease has been spreading there for weeks, generally among the area’s young and unvaccinated population. The outbreak, which took hold in an area that used to be a stronghold of the polygamist Fundamentalist Church of Jesus Christ of Latter-day Saints, has led to the hospitalization of four people on the Arizona side of the border.

Short Creek’s three-month measles outbreak is the second largest in the U.S. this year, trailing only the outbreak in West Texas that claimed the lives of two children. That outbreak lasted nearly seven months and resulted in 762 total positive cases by the time the state’s health department declared it over in mid-August. More than two-thirds of the cases were in children and nearly 100 people were hospitalized.

There are some signs that the Short Creek outbreak is slowing. The last week of November saw only three new positive cases in Mohave County, marking the lowest increase since the beginning of the month. Still, the outbreak isn’t expected to sputter out just yet.

The active outbreak in Short Creek will “eventually burn itself out,” said Will Humble, a former director of the Arizona Department of Health and Human Services. But Humble, who is now the director of the nonprofit Arizona Public Health Association, said he expects “this one to last longer at a slower boil than a typical measles outbreak.”

Located in the Arizona Strip — a lightly populated area cut off from the rest of the state by the Grand Canyon — Short Creek is isolated and has limited medical access. Instead of traveling south into Arizona for essential services, residents must go north, into Utah’s Hurricane and St. George, to receive any medical care that isn’t available in a local clinic. The emergency rooms in Hurricane and St. George are both currently under symptom watch after measles exposures at those locations.

On the Utah side of the outbreak, 12 people have been hospitalized, according to the state’s health department. It’s unclear whether those individuals are all Short Creek residents, as 30 measles cases have been reported in seven different counties in Utah. The most recent Utah cases were identified in the counties surrounding Salt Lake City, although it’s not clear if those cases are connected to the outbreak along the border.

Arizona had measles exposures in Flagstaff and at a Tate McRae concert in Phoenix, which Humble said was likely connected to Short Creek’s outbreak. No additional cases have been reported from those exposures. 

Short Creek’s culture of homeschooling children also results in the outbreak acting differently. Measles loves to fester in schools — and Colorado City’s have poor vaccination rates — but with so many students homeschooled, outbreaks in schools have been somewhat limited. Hildale’s Water Canyon Elementary School is currently under symptom watch and has been the site of multiple positive cases over the course of the outbreak. Three Falls Elementary School in Hurricane is also currently under symptom watch. No Colorado City schools have closed. 

With mostly large, homeschooled families to run through, the measles outbreak is less likely to burn bright and fast through the community and more likely to spread slowly and methodically. It’s unlikely to happen before the end of the year, but eventually, everyone in the Short Creek area will likely either get vaccinated or contract measles and recover before health officials declare the outbreak is over. 

An area must have 42 days — or two incubation periods — occur before that declaration can be made. If one new case emerges, that clock resets as “one case is an outbreak when it comes to measles,” said Humble. Here’s hoping Short Creek residents stay away from any more Phoenix concerts for a while.

Until then, a slow, weekly trickle of new cases is likely to be the norm. Short Creek is small, and the ultimate case total probably won’t challenge the West Texas outbreak for the largest in the country. But Humble said the true case count could be higher than health officials know. 

“There are undoubtedly cases that are not counted,” Humble said. “If the parents are dealing with it at home and don’t take them to the doctor, then those cases just never get counted.”

“But,” he added, “it will end.”