CDC Warns Doctors About a Mystery Bacterial Outbreak With No Clear Origin

It's unknown how three people in three states caught the often-fatal tropical disease melioidosis, which isn't normally transmissible between humans.

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A photo of Burkholderia pseudomallei cultured in chocolate agar after three days time
A photo of Burkholderia pseudomallei cultured in chocolate agar after three days time
Photo: Todd Parker/CDC

The Centers for Disease Control and Prevention is warning doctors about a strange cluster of illness in three states caused by a rarely seen bacteria in the U.S., one that’s killed at least one person and hospitalized two others so far. The illness, called melioidosis, can be highly fatal but isn’t normally considered contagious between people. Officials don’t know how these victims contracted the bacteria, though the cases do seem to be connected.

Since March 2021, the CDC announced in a health alert on Wednesday, at least three people in three non-adjacent states (Kansas, Texas, and Minnesota) are known to have contracted melioidosis. The first victim, a man with preexisting lung and liver issues, died 10 days into his hospitalization. The other two, a woman and child, were identified in May. And while one patient has since been discharged to a transitional care unit, the other remains hospitalized.

“The CDC is working with state health officials in Kansas, Texas, and Minnesota to investigate three cases, including one death, of a rare, but serious bacterial infection called melioidosis,” a CDC representative told Gizmodo in an email.

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Melioidosis, also called Whitmore’s disease, is caused by the rod-shaped bacteria Burkholderia pseudomallei and can affect many species of animals and humans. Its symptoms are non-specific, resembling many other diseases, and depend on where the infection is located in the body. Most infections cause fever, for instance, but in the respiratory tract it may cause cough, chest pain, and reduced appetite. It also can spread to the bloodstream, where it’s capable of causing life-threatening sepsis, and can even reach the brain or nervous system. Because it’s hard to diagnose melioidosis (some automated tests can even mistake the bacteria for another species, which happened in the first case), appropriate treatment is often delayed. But even with aggressive antibiotics given through IV, it’s still regularly fatal, killing between 10% to over 40% of its victims once symptoms begin. It can also lie dormant in the body, not causing illness until a person’s health declines for other reasons.

B. pseudomallei naturally lives everywhere in the soil and water of tropical environments, and that’s usually how people come into contact with it, particularly after a rainy season where the earth is disturbed. It has been known to become aerosolized and capable of spreading through the air and between animals or people, though only on rare occasions. Still, its high lethality, hard-to-trace nature, and airborne potential has led governments like the U.S. to consider it a bioterror threat, on par with other germs like Ebola, smallpox, and anthrax.

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“Melioidosis is a serious neglected tropical disease of Southeast Asia, India, and Australia where it is a major cause of pneumonia, abscesses and sepsis. The fact that it may be gaining a foothold in the U.S. is concerning,” Peter Hotez, dean for the National School of Tropical Medicine at Baylor College of Medicine in Texas, told Gizmodo in an email.

According to a report from The Center for Food Security and Public Health at Iowa State University, the bacteria has never been found in the natural environments of North America, at least as of January 2016 when the report was last updated. So when cases in the U.S are rarely identified, they’re usually traced back to travel to a country where it’s endemic. That doesn’t seem to be the explanation here, though, since none of the patients’ families had reported any travel out of the country or far from their homes lately. But the cases do appear to be linked in some way, because all three were infected with genetically similar strains of the bacteria.

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“Testing suggests a common source of infection, but that source has not yet been identified,” the agency said. “CDC is working with states to assess exposures or products these individuals have in common, as well as environmental samples from the states where cases have been identified. Additionally, CDC experts are providing epidemiologic assistance to help investigate the cause of infection.”

The CDC does think some theories for the outbreak are unlikely. According to William Bower, epidemiology team lead at the Bacterial Special Pathogens Branch of the CDC, the genetic analysis indicates that these patients have not caught B. pseudomallei from a natural reservoir in the U.S., since the strains found in the victims don’t resemble strains found elsewhere in the Americas.

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“At this time, there is no evidence to suggest the cases under investigation are the result of a biological attack,” he added.

For now, the CDC considers the risk to the public to be low. But this outbreak is a mystery that bears solving, especially if there’s a common source still around that could sicken others. Melioidosis in general is thought to be understudied and underappreciated as a source of illness. Though it’s estimated to kill at least 89,000 people worldwide every year, for instance, the toll may very well be higher.

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In its alert, the CDC asks doctors to consider melioidosis as a possible diagnosis for compatible symptoms, even if there’s no travel history; it also asks them to consider rerunning tests using automated identification if they’ve come across the several other bacteria that B. pseudomallei can be mistaken for.

“CDC encourages healthcare workers to be aware of the potential for more cases and to report cases to their state health departments,” the CDC said.

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Alfredo Torres, a microbiologist and immunologist at the University of Texas Medical Branch, has studied and consulted on cases of melioidosis in North America. This year, he co-authored a case report about two children in Sonora, Mexico who died from the illness in the fall of 2018, possibly from an endemic source in the area.

Given the CDC’s genetic evidence, he said, he agrees with their current assumption that these cases are likely not linked to natural reservoirs of the bacteria that may have reached the U.S. from elsewhere in the Americas. He also said a biological attack is very unlikely.

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“Therefore, the obvious avenues to investigate are soil imported from other countries that are endemic and that might carry the bacteria, potential food or water contaminated with the bacteria, or some pets that might be infected (CDC has reported melioidosis cases in U.S. people that have an iguana or a fish as a pet),” he told Gizmodo in an email.

At the same time, he and his colleagues have found the bacteria in Mexican soil, and he said it’s theoretically possible that the germ could establish itself in some parts of the U.S. if introduced. The warming climate will also allow melioidosis to reach places it wouldn’t have otherwise, he noted. So while this current cluster might be an isolated incident, and melioidosis isn’t likely to spark the next pandemic, it’s certainly a growing concern in his eyes.

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“Due to changes in weather patterns, some pathogens that normally were not present in a particular area might start causing disease. Therefore, it is important to make the health professionals aware of this pathogen and the disease that it causes, so quick identification can be done and treatment is properly used to save lives,” he said. “Without that, it might be too late for the next melioidosis patient when the proper diagnosis is done.”

This article has been updated with comments from Alfredo Torres and Peter Hotez.