The melioidosis-causing bacteria recently detected in U.S. soil samples is not likely related to a 2014 “lab leak” in Louisiana, nor to a recent outbreak sparked by an aromatherapy product, experts said.
Genetic sequencing indicated the strain of Burkholderia pseudomallei detected in southern Mississippi is from the Western hemisphere, similar to isolates found in the Caribbean or Latin America, said Alfredo Torres, PhD, of the University of Texas Medical Branch in Galveston.
Isolates from the recent melioidosis outbreak tied to aromatherapy products from Walmart were traced back to a lineage in India, where the products were manufactured. The strain identified in the accident at the Tulane National Primate Research Center in Covington, Louisiana, was a southeast Asian strain typically used in research, Torres said.
The bacterial special pathogens branch at CDC confirmed, in an emailed statement to MedPage Today, that the current strain is genetically distinct from the other two strains and “is a new one that has not been seen previously.”
The genetic sequences from the most recent samples are not publicly available, the CDC said, but noted that sequences from the strain involved in the aromatherapy outbreak were published in the New England Journal of Medicine.
Novel Western Hemisphere Strain
CDC announced on Wednesday that B. pseudomallei was detected for the first time in U.S. soil samples from the Gulf Coast region in southern Mississippi, raising concerns that this bacteria that has previously been limited to tropical and subtropical regions might be becoming endemic in the U.S. The bacteria can cause melioidosis, a disease with a case fatality rate in the range of 10-50%.
Environmental sampling in June 2022 was prompted by two U.S. cases, one in July 2020 and another in May 2022. The patients — both of whom recovered — lived in close geographic proximity in southern Mississippi, according to the CDC’s Health Alert Network advisory.
The agency sampled household products along with soil and water in and around both patients’ homes. Three samples that were taken from the soil and puddle water of the property of the 2020 case were positive for the bacteria. CDC said this suggests the environmental bacteria was the likely source of illness — and that it’s been present since at least 2020.
“Because there were two cases in close geographical proximity infected by the same strain, and positive environmental samples from one of the patient’s property, we can say that it is at least locally endemic to this area,” the CDC statement to MedPage Today said.
CDC calls it a “novel” strain from the Western hemisphere that’s distinct from previously known isolates.
In November 2014, seven research rhesus macaques at the Tulane National Primate Research Center were infected with B. pseudomallei, even though they hadn’t been involved in experiments with the bacteria there. A CDC statement on the agency’s investigation said the animals were in the breeding colony when they were infected, not in the laboratory.
While a specific transmission event was never identified, the investigation found safety lapses at the facility that could have led to transmission, including incorrect use of outerwear to prevent clothing from becoming contaminated.
This “could have led to the bacteria clinging to inner garments and getting carried out of the select agent lab where research was being conducted with the bacteria on mice,” the CDC report stated. “The bacteria could have been transferred this way to the breeding colony where the non-human primates resided and/or to the clinic where routine examinations and treatments were administered.”
The strain identified in the outbreak was 1026b, which was originally recovered from a rice farmer who was sickened in Thailand in 1993, the CDC told USA Today in 2015 — thus unrelated to the Western hemisphere strain reported in the current sampling.
The agency concluded that there was no evidence the bacteria had been released into the surrounding environment.
Four cases from four states were involved in the melioidosis outbreak related to products from Walmart: a 53-year-old woman from Kansas, a 4-year-old girl from Texas, a 53-year-old man from Minnesota, and a 5-year-old boy from Georgia.
It took a long time to find the source of the outbreak, but ultimately a sample taken from a second visit to the Georgia boy’s home revealed the culprit. Researchers determined the strain matched bacteria endemic to India where the product was made.
Walmart pulled the spray — Better Homes & Gardens Lavender & Chamomile Essential Oil Infused Aromatherapy Room Spray with Gemstones — from store shelves and stopped shipment of the product from its warehouses in October 2021.
As of May, the facility in India where it was manufactured had not determined the exact source of contamination, the CDC previously told MedPage Today.
Torres said it’s not surprising that the bacteria was detected in U.S. soil. He pointed to a 2016 Nature Microbiology paper that predicted some soils in southern U.S. states would be able to host B. pseudomallei.
“It is quite possible that climate changes are letting the pathogen [find] a new niche for survival in the soil and instead of being deep down from the surface, the pathogen is now on the surface and individuals can get infected with it,” he told MedPage Today in an email.
As for next steps, the CDC said it is “discussing with partners sampling strategies to improve our understanding of the geographic distribution of this bacteria in the environment in the U.S.”