Two Islip Town residents came down with symptoms of West Nile virus in late September, both were hospitalized and only the patient who is younger than 50 has been released, officials said on Wednesday.

So far this year, Suffolk has reported five cases of West Nile virus, including three identified in early October, Health Services Commissioner Dr. James Tomarken said in a statement.

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All three of those patients, from the towns of Brookhaven, Islip and Smithtown, were treated for the mosquito-borne virus at hospitals and released.

About 20 percent of people who become infected experience “clinically noticeable” symptoms, health officials say.

The state’s mosquito season should end Nov. 1 and not start up until June 1.

People seeking more information can call the Department of Health Services at 631-854-0333.