An outbreak of arboviral encephalitis was first recognized in New York City in late August and has since been identified in neighboring counties in New York state. On the basis of these findings, aerial and ground applications of mosquito adulticides and larvacides were instituted in northern Queens and South Bronx on September 3.
Surveillance is also ongoing in surrounding areas.
A clinical case is defined as a presumptive diagnosis of viral encephalitis with or without muscle weakness or acute flaccid paralysis, Guillain-Barre syndrome, aseptic meningitis, or presence of the clinical syndrome characterizing the initial cluster of cases in a patient presenting after August 1. Before and concurrent with this outbreak, local health officials observed increased fatalities among New York City birds, especially crows. Necropsies performed on these birds at the zoo revealed varying degrees of meningo-encephalitis and severe myocarditis. NVSL isolated viruses from the birds' tissues and forwarded them to CDC on September 20 for identification and characterization. In other tests at CDC, flavivirus antigen was detected in one of the autopsy specimens by immunohistochemistry, and a West Nile-like virus genomic sequence identical to that derived from the bird isolates was observed in a human brain specimen from an encephalitis case.