(NEXSTAR) – The Centers for Disease Control and Prevention on Monday confirmed another fatal case of melioidosis, a rare infectious disease typically found in tropical regions including Southeast Asia and northern Australia.

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Four total cases have been observed this year in four different states: Georgia, Texas, Kansas and Minnesota. The CDC said two of those cases were fatal, including the latest melioidosis infection in Georgia.

The CDC believes the cases are linked but has yet to determine a common source of Burkholderia pseudomallei, the bacteria that causes the infection, that all four patients may have been exposed to. None of the patients traveled internationally, the CDC noted, adding that they were all spread apart geographically when symptoms began. They were also sickened at different times.

Melioidosis is usually caused by contaminated soil or water, and rarely spreads from person to person, the CDC says. To that end, health officials have collected soil, water and product samples from the patients’ homes. However, the CDC believes the most likely cause of the cases is a common imported product, as Burkholderia pseudomallei “has also been found to contaminate wet or moist products” in the tropical regions where the bacteria are more commonly found.

In its press release, the CDC is asking doctors to consider melioidosis as a possible diagnosis in U.S. patients with acute bacterial infections, but whose illnesses are not responding to antibiotics.

“CDC also urges clinicians not to rule out melioidosis as a possible diagnosis in children and those who were previously healthy and without known risk factors for melioidosis,” the CDC wrote in Monday’s news release.

Symptoms of melioidosis are wide-ranging, but may be similar to those of tuberculosis or pneumonia, the CDC says. Among them, patients may experience localized or disseminated infections, causing fever, headaches, weight loss or possible seizures, among other symptoms. Lung and bloodstream infections may also occur, causing respiratory issues, chest pain, joint pain, disorientation and more.

Treatment generally involves intravenous antimicrobial therapy for a duration of up to eight weeks, followed by months of oral antimicrobial therapy.

Medical experts say people with underlying conditions including diabetes, liver or kidney disease, cancer or chronic lung disease are at increased risk for melioidosis, though it can affect otherwise healthy people. Two of the four patients infected with melioidosis in the U.S. had no underlying conditions, the CDC says.

Melioidosis is also an increasing concern for the U.S. Department of Defense, particularly in regards to bioterrorism threats. In June, the Department of Defense awarded a $3 million contract to University of Hawaii at Manoa’s School of Life Sciences to develop a vaccine for melioidosis, KHON2 reported.