The virus - which is spread by mosquitoes - has been responsible for the deaths of two elderly people in the city's Queens district since the outbreak was reported last week.

Three other cases have been confirmed and public health officials have acted to quell fears the virus could spread out of control.

In total 37 people are suspected of having the infection in the New York metropolitan area.

Pool breeding

Health officials used helicopters to spray the spray the pesticide malathion in parts of the Bronx and Queens in the hope of killing the mosquitoes carrying the virus.

One official said stagnant water was the likely breeding ground for the disease-carrying insects.

Jerry Hauer, of the office of emergency management, said: "We found over 150 swimming pools which had stagnant water in them.

"They had not been used for the majority of the summer they had this kind of green murky water in it."

Residents have been complaining to radio shows and asking why the authorities did not act faster.

Political responsibility

In 1983 the city ended its fumigation programmes after state officials banned the practice due to environmental concerns, said Bronx councillor Peter Vallone.

Bronx borough councillor Fernando Ferrer said Mayor Rudolph Giuliani was to blame.

"Guiliani ignored requests for help from the Bronx council to refund a mosquito control program," he said.

Mayor Giuliani rejected the charges. "Ferrer says I'm even responsible for mosquito bites," he said.

The St Louis variety - the most common viral encephalitis in the US - produces flu-like symptoms such as fever, headaches and lethargy, and in severe cases high fever and convulsions.

The elderly are most at risk from the virus, with 30% of those infected dying as a result.