Health officials in Washington have announced the first confirmed human case of West Nile virus in the U.S. capital city.

The city's health director, James Buford, said in a statement Wednesday that a 55-year-old man tested positive for the mosquito-borne virus and has been hospitalized.

Washington officials also said Wednesday they found 40 mosquito pools in the district that tested positive for the West Nile virus. A mosquito pool is a group of about 25 mosquitos that were collected and tested for the virus as a group.

West Nile virus causes flu-like symptoms and can be fatal to the elderly and those with weak immune systems. It thrives in warmer climates and already has killed five people in the southern U.S. state of Louisiana so far this year.

The disease is common in parts of Africa and Asia. It first appeared in the United States in 1999 and has since spread to more than two dozen states and the District of Columbia.