Lyle R. Petersen, MD, MPH; Anthony A. Marfin, MD, MPH
Current Author Addresses: Drs. Petersen and Marfin: Division of Vector-borne Infectious Diseases, Centers for Disease Control and Prevention, PO Box 2087 (Foothills Campus), Fort Collins, CO 80522.
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. Information 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. Continued geographic expansion is likely. Overall, one in 150 infections 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 provide a clinical clue to the presence of West Nile virus infection. Peak incidence occurs in late summer, although onset has occurred 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 possible 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.
Table 1. Key Clinical Facts about West Nile Virus in North America
States reporting epizootic activity and human infections of the West Nile virus, 1999–2001.
Week of symptom onset for persons reported to have West Nile virus infection, 1999–2001.
Transmission cycle of West Nile virus.
Table 2. Symptoms of West Nile Virus Reported among Hospitalized Patients during Outbreaks in New York State (1999), Romania (1996), and Israel (2000)
Table 3. U.S. National Case Definitions for West Nile Encephalitis
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Petersen LR, Marfin AA. West Nile Virus: A Primer for the Clinician. Ann Intern Med. 2002;137:173-179. doi: 10.7326/0003-4819-137-3-200208060-00009
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Published: Ann Intern Med. 2002;137(3):173-179.
CNS Infections, Infectious Disease, Neurology.
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Print ISSN: 0003-4819 | Online ISSN: 1539-3704
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