The West Nile virus has been detected in 19 mosquito samples in Suffolk County taken at the end of July, county health officials have announced.

The new positive tests bring the total this year in Suffolk to 37, more than doubling the number reported a week ago. Despite the increase, that’s still down from 46 samples that had tested positive at the same time last year.

“The confirmation of West Nile virus in mosquito samples or birds indicates the presence of West Nile virus in the area,” Suffolk County Health Services Commissioner James L. Tomarken said in a news release. “While there is no cause for alarm, we advise residents to cooperate with us in our efforts to reduce the exposure to the virus, which can be debilitating to humans.”

The positive samples of the species Culex pipiens-restuans were collected on July 27 and 28 in Huntington Station, Northport, Farmingville, Selden, Port Jefferson Station, Stony Brook, Setauket, Bay Shore, Aquebogue, Nesconset, Holtsville and Greenlawn.

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Four birds tested had the virus this year in the county, but no people or horses, so far, according to the news release.

The virus has been found in Suffolk every year since it was first detected in 1999.

Most people who contract West Nile have no symptoms or mild symptoms, according to the news release. Some people, however, can develop severe symptoms and suffer permanent neurological damage, and the health department warned that people should take precautions to avoid being bitten by mosquitoes.

Last year 57 people in New York state were infected with the virus, and five of them died, according to the Centers for Disease Control and Prevention. New York had the eighth-highest number of cases nationwide in 2015, according to the CDC.