NEW YORK – Public health and commercial laboratories are bringing molecular and serology testing online to help manage the ongoing measles outbreaks in Texas and New Mexico.
While public health labs have sufficient capacity to handle the current case numbers, declining childhood vaccination rates could lead to larger outbreaks and increased demand for testing in coming years, suggested one clinical lab executive.
According to the US Centers for Disease Control and Prevention (CDC), as of March 13, 301 measles cases had been confirmed across 15 states. The bulk of those cases have occurred in Texas, which as of March 18 had confirmed 279 infections, most of those in Gaines County, which sits at the state's western border. New Mexico has experienced a smaller outbreak, with 38 measles cases confirmed as of March 18.
During a recent media call hosted by the College of American Pathologists, Ben Bradley, medical director of virology at ARUP, said these numbers were likely undercounts.
"Knowing the true impact of these highly transmissible viral events is challenging," he said. "The numbers we are putting out right now are the confirmed cases that we have been able to document, but we know that the spread is probably greater than that, that this is an underestimation."
Because measles is a relatively rare disease in the US, most testing capacity is in public health labs, said Kelly Wroblewski, director of infectious disease programs at the Association of Public Health Laboratories. "There's not enough volume to really justify maintaining capacity in [commercial] laboratories."
Several tests are being used to manage the outbreaks, Wroblewski said. PCR testing is most commonly used and is the most helpful for making a diagnosis. In the case of measles, testing may also include a second PCR assay called the measles vaccine assay, which allows clinicians to distinguish between viral genetic material present due to an infection from genetic material present due to recent vaccination. The test, which is used as a reflex test following a positive result, distinguishes between the measles strain used in vaccines and the wild-type strain, and "is important during an outbreak when an active vaccination campaign is happening," Wroblewski said.
Genotyping is also commonly done to establish the genotype of the virus in infected individuals. Wroblewski said that thus far all the Texas and New Mexico infections have been caused by the D8 genotype, which has been involved in a number of recent outbreaks globally.
Serology testing is also available, though Wroblewski said it has limited utility in highly vaccinated populations. It can be useful for testing individuals who have been exposed but are outside the window in which a PCR test would pick up the virus, she said, noting that IgM antibodies to the virus, which indicate a recent infection, typically linger a bit longer in the body than does the virus's genetic material.
There are no US Food and Drug Administration-cleared in vitro diagnostics for measles. In Texas, the Department of State Health Services (DSHS) laboratory in Austin offers molecular testing for the virus as does the state's Laboratory Response Network's Lubbock facility, said DSHS spokesperson Lara Anton. She said the state's El Paso and North Texas LRN laboratories are also planning to bring molecular testing for measles online soon.
In New Mexico, all measles testing is being done through the state Department of Health's Scientific Laboratory, which New Mexico DOH spokesperson David Morgan said is, to his knowledge, the only lab in the state that does molecular testing for the virus. He said the state's current testing needs are well covered by the lab's existing capacity and that it provides results within 24 hours.
While public health labs have largely handled measles testing thus far, commercial labs including Quest Diagnostics and Laboratory Corporation of America offer serology and PCR testing for the virus, and others are adding molecular measles tests to their menus. Denton, Texas-based infectious disease testing firm HealthTrackRx is launching a PCR test for the virus this month. Jay Reddy, the company's CSO, said it is not developing the test in response to the current outbreak so much as to prepare for the possibility of larger and more frequent measles outbreaks in the future.
Reddy said that for the last several years HealthTrackRx has received requests from physician customers for molecular testing for measles. This, combined with declining measles vaccination rates, led the company to develop a test.
"It's kind of a protective measure," he said. "If you continue to have an outbreak of 150 to 250 people in a region of Texas or New Mexico, that's not that big a deal. But if you get to the point where you are reaching thousands [of cases] … that testing line might be of value then."
Reddy said that, in particular, physicians the company works with appear interested in testing to prevent spread within their own offices in the event of a large outbreak.
According to the CDC, over the last four years, the percentage of US kindergartners vaccinated against measles has fallen from 95.2 percent during the 2019-2020 school year to 92.7 percent during the 2023-2024 school year.
"When you look at the overall landscape, you say, this could be a [situation] where a larger outbreak could occur, and at that point you would need a public-private kind of relationship to support higher volume testing," Reddy said.
He said HealthTrackRx will be able to run around 1,000 samples per day at launch of the test with the ability to expand from there if needed. He added that while the company expects most testing to continue to go through public health labs, it does have a large number of clients in the affected regions and has received requests for testing from some of those clients.
Reddy said that HealthTrackRx developed its test with guidance from the CDC, which provided advice on items including where to source material for validating the assay.
ARUP's Bradley said his lab offers serology testing and is also developing a molecular measles test that it plans to launch in mid-April.
As laboratory-developed tests, measles molecular assays are subject to the FDA rule on LDTs, including new reporting requirements set to go into effect in May. Tests that were on the market prior to release of the rule in April 2024 may be exempt from later stages of the rule's implementation, including premarket review requirements. The newly developed tests from the Texas LRN labs and HealthTrackRx and ARUP, on the other hand, may be subject to these requirements.
The FDA has issued draft guidance detailing how it may offer enforcement discretion of LDTs both in cases where it has implemented Emergency Use Authorization authority and in situations where it has not but in which testing may nonetheless be needed to respond to a health emergency. The agency has not finalized this guidance, however, and, in any case, it is unclear if it would apply to current or future measles testing needs.