Something alarming happened in Mesa County in August: In the span of a few days, public health officials identified two new people with measles. Even worse, both of them caught the virus locally from an unknown source.
Was this the beginning of a long-feared major outbreak?
“That did certainly represent challenging circumstances, starting from an unknown case,” said Dr. Rachel Herlihy, the deputy chief medical officer at the Colorado Department of Public Health and Environment.
But, rather than scrambling, Mesa County public health leaders were well prepared to respond because they had received an early tip. The poop knew.
A couple days before the first case was identified, CDPHE detected the measles virus in the Mesa County sewer system. The agency notified Mesa County, which stepped up preparations for a potential outbreak.
That early detection allowed Mesa County to get ahead of the virus before it began running undetected through the community. And now the county appears to be measles-free, with no new cases identified in weeks and the incubation windows having closed for people who were potentially exposed by earlier cases.
“The response really highlighted how critical vaccination, early detection and strong partnerships with medical providers are in preventing future outbreaks,” said Kathleen Satterfield, an epidemiologist supervisor with Mesa County’s public health department.
The experience also shows how use of wastewater testing has evolved in Colorado.
The testing began during the COVID pandemic as a tool for public health officials to conduct disease surveillance — tracking big-picture ebbs and flows when lots of people are getting infected. But the Mesa County outbreak shows how the state is now looking to use wastewater for detection of new viruses that may have so far only infected one or two people. The state launched a pilot project to look for measles in wastewater in the spring.
“This is a good example of how I see wastewater surveillance being used in the future as an early warning system for these emerging targets,” said Allison Wheeler, the wastewater surveillance unit manager at CDPHE and the co-director of the Colorado Wastewater Center of Excellence.
The concept is pretty simple. People who are infected with a virus shed that virus when they use the bathroom. The wastewater detection system takes samples — before you retch, the samples are taken from the entire wastewater stream, which just looks like slightly murky water — and then tests them for the presence of various viruses.
Wheeler said tests from Mesa County first returned a low-level detection for measles in early August followed by a higher-level detection. That was enough to signal that it was legit, and the state alerted Mesa County.
The system can’t identify how many people are infected or precisely where they are. But it can allow public health authorities to get an early jump.
“People are still skeptical of wastewater surveillance because it’s a new science,” Wheeler said. “So we really have to work to say it works. And this was an example of when it worked.”
The outbreak ultimately grew to seven cases — some of those were people quarantining in the same household with people known to be infected. So far this year in Colorado, there have been 27 cases of measles, including five people who were hospitalized. There have been no reported deaths.
Of those infected, 70% have either been unvaccinated or had unknown vaccination status.
Satterfield said Mesa County had been preparing for measles to arrive in the county for months — ever since an outbreak in Texas began seeding infections in other states. Once it was confirmed, the agency swung into action, putting 27 staff members, as well as a five-member CDPHE team, to work interviewing people who were infected and tracking down their contacts.
The county held town hall meetings with health care providers to make sure they were watching out for signs of measles in their clinics and also worked with other agencies to get the word out.
“We couldn’t have acted on this response without all those involved,” she said. “It was quite an undertaking.”