Rationale:

• Clinical findings are nonspecific and need to be confirmed with serologic studies.

Evidence:

• Consensus recommendations dictate that WNV should always be considered in unexplained meningitis or encephalitis, especially in elderly patients in late summer or early fall (1).
• Expert consensus suggests that the diagnosis of WNV meningitis, encephalitis, or other neuroinvasive syndromes cannot be made on clinical grounds alone because the presentations are not specific to the diseases (6).
• The development of an IgM antibody-capture ELISA for the detection of medically important arthropod-borne viruses in serum and CSF has made diagnosis more efficient (34).

Comments:

• The primary means of diagnosis is serology. However, sensitivity of antibody tests of acute-phase serum may be lower among patients with WN fever than those with WN neuroinvasive disease. Limited data suggest that patients with WN fever do not have demonstrable antibody in serum obtained within 8 days of clinical onset and can only be documented to have WNV infection after NAAT tests or convalescent-phase samples are obtained (35). This is a noticeable difference between the diagnostic algorithms for WNV and for enteroviral or herpes encephalitis.
• Tests of serum or CSF are available commercially and can be obtained through local, state, or province (in Canada) health departments for patients with encephalitis or meningitis. In some instances (e.g., fatal cases, immunosuppressed patients), the use of nucleic acid amplification testing or virus isolation may be considered if serologic test results are negative.
• Encourage autopsy in fatal cases to isolate the virus and better characterize pathologic changes, especially in brain and spinal tissue.