Mosquito surveillance has detected 293 WNV-positive mosquito pools in 11 states and the District of Columbia , representing 12 mosquito species.

Traces of the virus have also been detected in mosquito pools or dead birds in the city's other four boroughs, but no spraying is planned there yet.

State officials have so far found 15 infected birds and 35 infected mosquito pools in Suffolk County, most of them in western towns.

In New Jersey, the hardest-hit state, there are already 19 infected birds and 13 mosquito pools.

As officials await await more testing news, Middlesex County, with 12 infected birds and 3 West-Nile-positive mosquito pools, has quietly emerged as an early hot zone.

In other words, areas where there tend to be more positive mosquito pools and positive crows or other birds.

Ground spraying began last night in the Bronx, where a new mosquito pool was identified, and in large swaths of Brooklyn, including Prospect Park.

Brooklyn was the last of the five boroughs to report finding the virus in birds or mosquito pools this year, Mr. Gadd said.

Twenty-seven mosquito pools - 23 in Staten Island, 3 in Central Park and one in Hunts Point, the Bronx - also tested positive.

The state government will order pesticide spraying only in certain situations including when a person who lives in an area has gotten sick and the proximity of infected mosquito pools to people.