The dangerous West Nile virus will probably spread beyond the Northeast, so doctors should consider that when diagnosing patients stricken with encephalitis or meningitis during mosquito season, researchers warn.
In a report on the Western Hemisphere's first known outbreak of the mosquito-borne virus, researchers urged physicians to aggressively test patients and report suspected cases to public health officials so new outbreaks can be controlled.
In the first outbreak, in the New York City area in the summer of 1999, at least 59 patients were hospitalized with West Nile infections. Seven died, and hundreds more had less serious infections. People with diabetes or those 75 or older were more than five times more likely to die than others.
Healthy people generally have mild flu-like symptoms, or none at all, when bitten by an infected mosquito. The researchers estimate only one in 100 West Nile infections causes symptoms.
The report, written by Dr. Denis Nash of the New York City Health Department and researchers from other health agencies, was published in Thursday's New England Journal of Medicine.
In an editorial, Dr. Kenneth L. Tyler of University of Colorado Health Sciences Center wrote that doctors must stay alert for clusters of unusual cases of illness, including outbreaks of disease in animals.
Late last summer, 14 human West Nile cases were reported in New York City and six in New Jersey, one of them fatal. By then, there were reports of birds killed by the virus from Vermont and New Hampshire south to North Carolina.