Measles crept into Utah and Arizona in June, with reports trickling into local health departments of patients coming to doctors and saying their children had just recovered from full-body rashes, and parents telling pediatricians that their whole family had just recovered from measles.
But because patients would decline testing, there were no official cases in the outbreak until August 8, when the Mojave County, Arizona, Department of Public health received a report about a 10-year-old boy who lived in a tightly knit community that spans the border of northern Arizona and southern Utah.
That outbreak has grown to more than 600 reported cases and is now the most active in the US. The Arizona-Utah cases will almost certainly be important to determining whether the US has lost its measles elimination status, meaning it’s stopped the routine transmission of the virus within its borders for over a year. The meeting to make that determination is now set for November.
The US Centers for Disease Control and Prevention tasked one of its disease detectives with using molecular evidence – clues buried deep in the genomes of the measles viruses that infected patients – to learn more about when the outbreak really started and how large it actually is.
The number of reported measles cases in the US jumped last year to 2,267, the highest total in more than three decades. Transmission has not slowed, with cases topping 1,700 in just the first four months of this year as the virus spreads through communities that have turned away from vaccination.
The US Centers for Disease Control and Prevention tasked one of its disease detectives with using molecular evidence – clues buried deep in the genomes of the measles viruses that infected patients – to learn more about when the outbreak really started and how large it actually is.
The number of reported measles cases in the US jumped last year to 2,267, the highest total in more than three decades. Transmission has not slowed, with cases topping 1,700 in just the first four months of this year as the virus spreads through communities that have turned away from vaccination.
Photo Illustration by Jason Lancaster/CNN/Getty Images
Tracing the origins of an outbreak
Almost as soon as the Utah outbreak was confirmed, health officials suspected that the true number of patients was bigger than they knew.
Most disease outbreaks are undercounted because doctors may miss diagnoses of unfamiliar diseases and patients may not seek medical care for religious or cultural reasons. Both factors seemed to be at play in this outbreak.
Measles has not circulated widely in the US in 30 years, so many doctors have never seen a case. Additionally, the community where measles is spreading has been the home of a sect of the Fundamentalist Church of Jesus Christ of Latter-Day Saints, a group that had a charismatic leader named Warren Jeffs who sowed distrust in vaccines.
The measles vaccine is highly effective. Two doses prevent disease roughly 97% of the time. Because the virus is so contagious, lingering in air for up to two hours after a person leaves the room, high vaccination coverage in an area, more than 95%, is needed to stop it from spreading. But misinformation campaigns and a lack of trust in public health officials have caused population-level protection against the virus to plummet.
Public health departments working to combat the outbreak wondered whether it might be possible to estimate when it really started, as well as its true size, by looking at how the genome of the virus had changed over time, according to Dr. Annie Wang, an Epidemic Intelligence Service officer who was assigned to Arizona’s Pima County Health Department during the outbreak.
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