The Outbreak of West Nile Virus Infection in the New York City Area in 1999

THE OUTBREAK OF WEST NILE VIRUS INFECTION IN THE NEW YORK CITY AREA IN 1999 Nash D, et al.N Engl J Med2001;344:1807: This is a report by the “1999 West Nile Outbreak Response Working Group” for the cluster of cases in the New York City area in 1999. The surveillance program included requesting hospitals in the New York City area to report suspected cases of viral infections involving the CNS. Suspected cases were patients who were hospitalized after August 1, 1999 with a presumptive diagnosis of viral encephalitis. In addition, weekly telephone inquiries to specialty areas of each hospital were conducted. Serum and CSF samples were requested from patients who met the clinical criteria. Laboratory definition of infection with WNV included: (1) evidence of the virus by RT-PCR; (2) WNV IgM antibody in CSF (EIA); (3) fourfold rise in antibody titer in serum or CSF by plaque-reduction neutralization; or (4) WNV IgM plus IgG antibody in a single serum sample (EIA). Using these criteria, there were 719 suspected cases on the basis of clinical presentation and 59 who satisfied the laboratory criteria. The clinical characteristics in these cases are summarized in Table 8:TABLE 8: Characteristics of West Nile virus infection, New York City, 1999, 59 casesThese 59 cases occurred during August and September 1999, the median age was 71 years, the overall attack rate was estimated at 6.5/million population and was strongly associated with advanced age, most of the patients had clinical signs of encephalitis, there were seven deaths (12%), muscle weakness was found in 27% and flaccid paralysis in 10%, nerve conduction studies indicated axonal polyneuropathy, and there did not seem to be an association with the immunocompromised state. The authors conclude that this diagnosis should be considered in the differential diagnosis of encephalitis and viral meningitis that occurs in the summer and especially in patients who are older and those who present with muscle weakness as a prominent feature.