A person in Mexico has died after contracting a strain of bird flu that hasn’t been confirmed in humans before, the World Health Organization said Wednesday.

The virus was detected in a 59-year-old who had been hospitalized in Mexico City. The person died one week after developing a fever, shortness of breath and diarrhea. It’s the first lab-confirmed case of a person contracting a form of bird flu known as H5N2, the WHO said in a statement, raising questions about a strain that has largely been under the radar. The current bird flu outbreak in U.S. dairy cows is being driven by a different strain — H5N1.

The patient, who lived in central Mexico, had no history of exposure to poultry or other animals and had underlying medical conditions. The Mexican government doesn’t know where the patient was exposed to the virus, though the strain of avian influenza has been reported in poultry in the Mexican state where the person lived.