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Date: Mon, 28 Oct 2002
Posted by: Bryon P. Backenson (bpb01@health.state.ny.us)

I may be wrong, but I believe that the "1 in 150" figure came not from the serosurvey done in Queens in 1999, but from the serosurvey done in 2000. This serosurvey was done in 3 locations (Staten Island NY, Suffolk County NY, Fairfield County CT), each of which covered a greater geographic area than the 1999 serosurvey did. The study consisted of taking blood and completion of a lengthy questionnaire. Approximately 750-850 individuals had blood drawn in each location, for a total of about 2400-2500 individuals. Using the number of positives found, the populations of the area, and the number of hospitalized cases in each area, CDC crunched the numbers. The result were the figures we've seen replicated in numerous news reports:

"Less than 1% of people in a given area will be exposed to West Nile virus."
"Of those people that are exposed, about 1 in 150 will develop symptoms that are serious enough to require hospitalization."

Sometimes the two statements above get misrepresented in the press.

I'm not sure if the data from 2002 will alter these figures any. I know that some locations are considering doing serosurveys, but to be done right, these are extremely time- and labor-intensive, particularly when you take into account the calculations that tell you the number of people required for statistical significance/adequate representation.

-- 
P. Bryon Backenson
Research Scientist and Assistant Director
Arthropod-Borne Disease Program
New York State Department of Health
ESP, Corning Tower Room 632
Albany, NY  12237
phone:  518-474-4568
fax:  518-473-1708
e-mail:  bpb01@health.state.ny.us

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