A person with prior health complications who had contracted bird flu died in Mexico in April and the source of exposure to the virus was unknown, the World Health Organization said.
The 59-year-old man had been hospitalized in Mexico City and died on April 24 after developing a fever, shortness of breath, diarrhea, nausea and general discomfort.
"Although the source of exposure to the virus in this case is currently unknown, A(H5N2) viruses have been reported in poultry in Mexico," WHO said.
It was the first laboratory-confirmed human case of infection with an influenza A(H5N2) virus globally and the first avian H5 virus reported in a person in Mexico.
Scientists said the case is unrelated to the outbreak of H5N1 bird flu in the United States that has so far infected three dairy farm workers.
Mexico's Health Ministry also said the source of infection had not been identified.
"The victim had no history of exposure to poultry or other animals but had multiple underlying medical conditions and had been bedridden for three weeks, for other reasons, prior to the onset of acute symptoms," the WHO said.
Mexico's Health Ministry said there was no evidence of person-to-person transmission in the case and farms near the victim's home were monitored. Other people in contact with the person tested negative for bird flu.
Bird flu has infected mammals such as seals, raccoons, bears and cattle, primarily due to contact with infected birds.
Scientists are on alert for changes in the virus that could signal it is adapting to spread more easily among humans.
