BOSTON — A number of U.S. individuals who traveled to Matamoros, Mexico, for surgical procedures requiring anesthesia returned home with a Fungal pathogen that caused meningitis — and a high percentage of the cases resulted in death, a researcher reported here.

By the most recent count, 151 individuals from the U.S. are under investigation for possible exposure to Fusarium solani, a dangerous fungal infection that is difficult to treat — especially when it invades the central nervous system — and a dozen deaths have been linked to the outbreak, said Dallas Smith, PharmD, an epidemiologist at the CDC’s Mycotic Diseases Branch.

In his late-breaking oral presentation at the annual IDWeek meeting, Smith said that CDC first got wind of the exposures on May 8 of this year, with two cases linked to epidural procedures in two clinics in Matamoros. By May 13, both of those clinics were shuttered by Mexican health authorities.

So far, the CDC has counted nine suspected cases of fungal meningitis, 14 probable cases, and 10 confirmed cases, Smith said. Three of the people with probable cases and nine of those who had confirmed cases have died.

Each year, more than a million Americans visit Mexico for medical tourism. Smith said the CDC worked with the Mexican Ministry of Health and developed a list of more than 200 people who had visited the two clinics and had undergone epidural anesthesia.

Fifteen of the people with fungal infections are of Hispanic or Latino descent (Matamoros is located just south of the Texas border on the Gulf of Mexico).

Most of the exposed patients were young women. Of the 205 cases of exposure identified, 188 were women and 17 were men. The average age was 35 (range 14 to 69). Smith noted that 145 of the exposures were among individuals in Texas, but some of the exposures included people from as far away as Alaska.

“All confirmed and probable cases from the United States and Mexico underwent procedural sedation by one anesthesiologist,” Smith noted. He said it is common that anesthesiologists formulate their own anesthesia and carry that formula with them from clinic to clinic.

A widely used anesthetic in Mexico did not seem to be a culprit medication, Smith said, but many anesthesiologists add morphine to their personal formula, often acquired through black market routes; the researchers speculate that contaminated morphine may have been used in these cases.

On average, symptoms related to the fungal infection began at 18 days following the procedure (range 0-58). The most frequent symptoms were headache, stiff neck, nausea, fever, light sensitivity, migraines, and vomiting. It took an average of 53 days post-procedure for the patients to be hospitalized, but the time to admission ranged from 14 days to 153 days after the procedure. Smith said that in some cases, lack of insurance delayed admission to the hospital.

“The message from this outbreak is: If you are thinking about traveling outside the United States or other Western countries for medical treatments: think twice,” said William Schaffner, MD, of Vanderbilt University Medical Center in Nashville, Tennessee, who was not involved in the research.

“You can never know in some countries if the treatments that are going to be injected in you are going to be safe, and not contaminated,” he told MedPage Today.

Schaffner said that one of the positive outcomes in this outbreak was the speed in which Mexican authorities acted to shut down the offending clinics. “Our relationships with Mexico have become more transparent, and things are much better now than they were years ago,” he said.

A problem with treating the mold infections in the brain stem — where they tend to locate — is that few therapies are effective, Smith said. Even amphotericin B, a workhorse antifungal is not greatly effective in these cases.

He said that treatment with manogepix might have utility in treatment. Six of seven patients treated with fosmanogepix — a pro-drug of manogepix — were discharged from the hospital. Eleven of 17 other patients treated without fosmanogepix died. Schaffner said that infection with F. solani creates such a dire situation, that the FDA has made fosmanogepix available to treat these rare infections even though the drug has not yet been approved.

Smith said successful treatment of F. solani infections has been hampered by antifungal allocation shortages, difficulty in obtaining isolates with mold meningitis, and difficulty in locating exposed patients.

He noted that the outbreak in Matamoros was similar to an outbreak in Durango, Mexico, in 2022 that saw 80 confirmed cases of fungal infections in patients, of which 41 died.