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Three patients developed difficult-to-treat Mycobacterium abscessus infections after receiving embryonic stem cell injections in Mexico in 2022, researchers reported.

Two men -- one from Colorado and one from Arizona -- acquired the infections in Guadalajara and Baja California, Mexico, from donor embryonic stem cell injections for joint pain, reported Minh-Vu H. Nguyen, MD, of National Jewish Health in Denver, and co-authors in .

The Arizona man (Patient B) had received an injection for psoriatic arthritis in the right elbow. The Colorado man (Patient C) had had bilateral knee injections for osteoarthritis, and developed infections in both knees.

"Historically, stem cell treatments have been linked to bacterial infections, and procedure-related infection risks associated with medical tourism are known," wrote Nguyen and co-authors. "Providers and public health agencies need to be aware of the risk for M. abscessus infections from stem cell treatments" not approved by the FDA, they added.

Previously, a Colorado woman (Patient A) had received intrathecal donor embryonic stem cell injections, also in Baja California, to treat her multiple sclerosis and also contracted an M. abscessus infection.

The researchers were only able to obtain original isolates from patients A and B, and performed whole-genome sequencing and phylogenetic analyses, which found that the two core genomes were distinct from known dominant circulating clones.

"Given that the isolates identified from patients treated at different, distant clinics represent a single clone, the physicians and CDPHE [Colorado Department of Public Health and Environment] suspect a common infected source (potentially the product, reagents, or equipment used) for patients A and B," noted Nguyen and co-authors.

The Baja California clinics where patients A and B were treated were 167 miles apart.

According to the CDC, M. abscessus is a distant relative of the bacterium that causes tuberculosis and leprosy. "People with open wounds or who receive injections without appropriate skin disinfection may be at risk for infection by M. abscessus," the . The mycobacteria is found in water, soil, and dust, and has been known to contaminate medications and other medical products.

M. abscessus is intrinsically drug-resistant and rapidly growing, according to Nguyen and co-authors, which can make it hard to treat with antibiotics normally used to treat skin infections. Symptoms can include fever, chills, and muscle aches.

The Arthritis Foundation recommends using caution in considering stem cell injections. "It's important to know that no stem cell interventions are currently approved by the FDA for any type of arthritis or joint injury, although you may see advertisements for them and read about celebrities getting these interventions," they wrote in a publication on .

Clinics offering stem cell therapies both in the U.S. and abroad can often target vulnerable patients, suggesting that the unproven therapies can treat chronic or incurable conditions. An investigation by MedPage Today last year found that patients were being harmed by autologous stem cell injections being sold as part of a "clinical trial."

The three patients are receiving ongoing care as of March 28, and no additional cases have been identified. The CDPHE attempted to contact the clinics that performed the stem cell injections, but did not get a response.

According to Nguyen and colleagues, the next steps will include performing whole-genome sequencing on new samples obtained from patient C, sharing the information, and continuing to look for other cases.

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