LONDON (Reuters) - American scientists have devised a new technique to detect West Nile virus which killed seven people in an unusual outbreak in New York last year.

The technique uses a sample of fluid taken through a spinal tap, or lumbar puncture, to detect the strain of the mosquito-borne disease.

``We have established a sensitive and specific real-time PCR method for detection of West Nile virus,'' Ian Lipkin, of the University of California, Irvine, said in a letter to The Lancet medical journal.

PCR, polymerase chain reaction, is a technique used to amplify a fragment of DNA to detect the viral sequence.

``Analysis of specimens obtained during the 1999 New York outbreak indicated the presence of viral sequences in cerebrospinal fluid of all of four individuals with fatal outcomes, and in only one of four who survived,'' Irvine and his colleagues added.

West Nile virus, which struck more than 60 people in New York, is usually found in Africa, West Asia and the Middle East.

The New York outbreak was the first in the Americas. The virus is spread from birds to mosquitoes to humans.

Government officials in the United States said last month that the virus will probably not be eliminated in the Western Hemisphere but added that it can be contained by controlling the mosquitoes that spread it.

Scientists have said children and the elderly are particularly vulnerable to the virus.