Suffolk County Commissioner of Health Services James Tomarken says an adult in his or her 50s contracted the virus and was hospitalized for five days last month for treatment.
The patient lives in the town of Brookhaven and is now recovering at home.
Last year, 14 human cases of West Nile were reported in Suffolk County.
To date this year, Suffolk County has reported 158 mosquito samples and four birds have tested positive for West Nile virus. No horses have tested positive this year.
West Nile virus can cause serious illness and, in some cases, death.
It is estimated that 20 percent of those who become infected will develop clinically noticeable symptoms, which include fever, headache and body aches, and occasionally a skin rash and swollen lymph glands.
To report mosquito problems or stagnant pools of water, call the Department of Public Works' Vector Control Division at 631-852-4270.
For medical questions related to West Nile virus, call the Department of Health Services: 631-854-0333.