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U.S. health officials are investigating the latest fatal case of a rare tropical disease typically found in South Asia.

The unidentified person, who died last month in Georgia, was the fourth U.S. case this year of melioidosis caused by a bacteria that lives in soil and water, the Centers for Disease Control and Prevention said Monday.

None of the cases from Georgia, Kansas, Minnesota or Texas traveled internationally, puzzling experts. The CDC said two died.

Federal health officials sent an alert about the latest case to doctors, asking them to consider melioidosis if they face a bacterial infection that doesn’t respond to antibiotics — even if the patient has not traveled outside of the country. The CDC said the infection is treatable if caught early and treated correctly.

Though the illnesses were found in different states at different times, the agency said lab analyses showed the infections were closely related.