The superbug that infected nearly a dozen Americans who recently underwent weight-loss surgery at a Tijuana hospital had a particularly nasty genetic mutation that set off alarm bells after patients began showing up in hospitals and doctors’ offices with painful wounds.

The U.S. Centers for Disease Control and Prevention issued a travel warning this week, notifying the public that 11 Americans who traveled to Tijuana hospitals for weight-loss surgery had become infected with drug-resistant pseudomonas aeruginosa infections during their stays.

Dr. David “Cal” Ham, a CDC medical officer, said Friday that the particular strain of pseudomonas bacteria involved in 11 confirmed cases had metallo-beta lactamase genes. Often called “VIM” by the epidemiological community, Ham explained that these genes cause the microbes that carry them to excrete enzymes that destroy carbapenems, a workhorse class of antibiotics with some of the broadest efficacy in medicine.

The pseudomonas strains that caused the Tijuana outbreak were already drug resistant, Ham said. Picking up carbapenem-fighting chops made an already serious threat more deadly.


“VIM makes this more concerning than your run-of-the-mill, drug-resistant pseudomonas,” Ham said.

One patient with an outbreak-linked infection has died, the physician said, though it’s impossible to say that it was just pseudomonas that caused that outcome.

“The patient who died did have a number of other underlying medical conditions, so we can’t say for sure if this infection was the primary cause of death,” Ham said.

Though six of the cases underwent bariatric surgeries at Grand View Hospital just south of the U.S. Mexico border, Ham said that so far not a single sickened patient was a California resident. Infected medical tourists came from seven states: Arkansas, Arizona, Oregon, Utah, Texas, Washington and West Virginia.


Some of the patients, Ham said, have received treatment with other antibiotics and have seen their infections subside while others are still in hospitals suffering as doctors work down a dwindling list of available options.

“There are still active infections, unfortunately,” Ham said. “Several of the isolates involved are susceptible only to a couple of, I would say, less-than-optimal antibiotics that have significant side effect profiles.”

Patients involved in the outbreak underwent surgeries from August through November with one case subsequently identified in 2015. Two additional suspected cases, Ham said, remain under investigation.

The CDC is urging doctors across the United States to report any cases of pseudomonas so that specialized testing can determine whether VIM or a handful of other problematic mutations that confer carbapenem resistance are present.


It was the CDC’s own Antimicrobial Resistance Laboratory Network that first sounded the alarm in the Tijuana outbreak. Pseudomonas samples are routinely sent to network-affiliated hospitals for analysis, and that’s where the VIM mutation became visible. But it’s necessary for doctors to report positive pseudomonus tests to the network in order for it to take analysis to the necessary next level.

Pseudomonas is relatively new to the VIM party. As of Sept. 30, 2017, only 84 cases nationwide have shown the mutation, Ham said. But other types of bacteria, especially enterobacteriacae and E.coli, have shown significantly higher rates of mutation.

Infectious disease specialists seek to isolate and treat patients infected with extra carbapenem resistance as quickly as possible because the genes that confer this extra protection are stored on structures called plasmids, which can easily move between different bacteria species. The idea is to kill these critters quickly before they have a chance to share their resistance genes with other types of bacteria.

“It’s important that we learn about these infections as quickly as possible so that very specific control measures and containment responses can be implemented,” Ham said.


When the CDC first issued its Tijuana travel warning this week, it said that the Mexican Government temporarily closed Grand View hospital, though it was apparent that the facility was still open Thursday evening. Mexican officials issued a short written statement Friday clarifying that the hospital’s surgery department, but not the entire facility, had been shut down pending an investigation.

Ham said the CDC has no access to the health records of patients involved, so it is difficult for American investigators to learn which surgical practices might have caused the infections.

So far, the CDC has said only that three other hospitals or clinics in Tijuana cared for the five patients out of 11 not cared for by Grand View. Those other hospitals were not mentioned by name in the CDC’s travel warning, Ham said, because they operated on only one or two outbreak patients, and the CDC could not determine that the number of cases was significantly greater than the facility’s normal rate of pseudomonas infection.

Correction: A previous version of this story misspelled pseudomonas. We apologize.


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