West Nile virus: A primer for the clinician

Abstract

This paper provides the clinician with an understanding of the epidemiologic and biological characteristics of West Nile virus in North America, as well as useful information on the diagnosis, reporting, and management of patients with suspected West Nile virus infection and on advising patients about prevention. Infor-mation was gathered from the medical literature and from national surveillance data through May 2002. Since the identification of West Nile virus in New York City in 1999, enzootic activity has been documented in 27 states and the District of Columbia. Con-tinued geographic expansion is likely. Overall, one in 150 infec-tions results in severe neurologic illness. Advanced age is by far the most important risk factor for neurologic disease and, once disease develops, for worse clinical outcome. Surveillance has identified 149 persons with West Nile virus–related illness in 10 states. Encephalitis is more commonly reported than meningitis, and concomitant muscle weakness and flaccid paralysis may pro-vide a clinical clue to the presence of West Nile virus infection. Peak incidence occurs in late summer, although onset has oc-curred from July through December. Immunoglobulin M antibody testing of serum specimens and cerebrospinal fluid is the most efficient method of diagnosis, although cross-reactions are possi-ble in patients recently vaccinated against or recently infected with related flaviviruses. Testing can be arranged through local, state, or provincial (in Canada) health departments. Prevention rests on elimination of mosquito breeding sites; judicious use of pesticides; and avoidance of mosquito bites, including mosquito repellent use. Ann Intern Med. 2002;137:173-179. www.annals.or