Diagnosis: West Nile Virus
• West Nile virus is a flavivirus that either causes subclinical disease or manifests as a febrile illness followed by changes in mental status.
• Overt disease is estimated to occur in 1 of 100 infected persons. Clinical disease develops primarily in elderly patients, who also have an increased death rate compared with an overall mortality rate of 12% for all hospitalized patients.
• Animal reservoirs for the virus include wild and domestic birds. The vectors are mosquitoes. The virus is thought to have been introduced into the United States by an infected migratory or imported bird.
• In recent years, cases of blood transfusion–associated West Nile virus infection have prompted the implementation of routine polymerase chain reaction testing of all blood donors.
• Immunohistochemical studies can be used to demonstrate cells infected with West Nile virus.
