Editor's Note: This story was updated at 3:50pm
An investigation by clinicians and public health officials from Colorado and Arizona has linked a cluster of antibiotic-resistant infections in three US residents to embryonic stem-cell injections at clinics in Mexico.
In a report published today in Morbidity and Mortality Weekly Report (MMWR), the investigators said the infections were caused by Mycobacterium abscessus, an intrinsically drug-resistant species of nontuberculosis mycobacterium that has previously been associated with medical tourism. The first patient, a Colorado woman (patient A) with multiple sclerosis, was treated for M abscessus meningitis at two Colorado hospitals (hospitals A and B) in November-December 2022 following an intrathecal donor stem-cell injection in Baja California, Mexico, in October 2022.
Two additional patients were identified at hospital B—National Jewish Health in Denver—in the spring of 2023. The first (patient B) was a man from Arizona who developed a right elbow osteoarticular infection following a donor stem-cell injection for psoriatic arthritis at a different clinic in Baja in April 2022. The second was a Colorado man (patient C) who developed infections in both knees after receiving stem-cell injections in his knees at a clinic in Guadalajara in October 2022.
“As a world-renowned referral center for patients with mycobacterial diseases, we see patients from all over the country, and we noticed a trend of patients getting this particular infection after stem cell injections were performed outside the U.S.," Charles Daley, MD, an author of the report and head of the division of mycobacterial and respiratory infections at National Jewish Health, said in a hospital press release.
All three patients were still undergoing treatment as of March. No additional cases have been identified.
Common source is suspected
Daly and his colleagues subsequently conducted whole-gene sequencing (WGS) and phylogenetic analysis of isolates from patients A and B and found that both were clonal M abscessus subspecies massiliense, nearly identical (with only one single nucleotide polymorphism between the core genomes), and distinct from dominant circulating clones, even though the clinics were 167 miles apart. That's when they notified state public health officials and the Centers for Disease Control and Prevention (CDC).
The authors of the report suspect the infections in patient A and B could have been caused by a common contaminated source (such as the product, reagents, or equipment used in the procedures). Attempts by the Colorado Department of Public Health and Environment to identify the product and gather more information about its administration have been unsuccessful, they said. The next steps will be to perform WGS on isolates from patient C and conduct prospective case finding.
"Providers and public health agencies need to be aware of the risk for M. abscessus infections from stem cell treatments for indications not approved by the Food and Drug Administration and maintain vigilance for similar cases," the authors wrote. "They also are advised to provide guidance for persons considering medical tourism."
Infections are among the many complications experienced by US residents who travel abroad for medical care. In a 2016 investigation reported in MMWR, CDC investigators described a multistate outbreak of M abscessus infections in 21 people who had undergone cosmetic surgery in the Dominican Republic. The CDC urges anyone who is considering medical tourism to consult their doctor first.
Providers and public health agencies need to be aware of the risk for M. abscessus infections from stem cell treatments for indications not approved by the Food and Drug Administration and maintain vigilance for similar cases.
