Acute Communicable
Disease Control

Contact Information
County of Los Angeles
Department of Public Health
Acute Communicable Disease Control
313 N. Figueroa Street, #212
Los Angeles, CA 90012
Phone: (213) 240-7941
Fax: (213) 482-4856

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(Back to West Nile Virus Main Page)
West Nile Virus Information for Medical Professionals

The Los Angeles County (LAC) Department of Public Health (DPH) reminds residents and clinicians that endemic West Nile virus (WNV) continues to affect county residents each year. In 2017, 268 cases of locally transmitted WNV were documented, 204 of which were neuroinvasive disease including 27 deaths.

Who Should be Tested for WNV
Medical providers should order WNV testing for all patients with aseptic meningitis, encephalitis, or acute flaccid paralysis during late spring through November when WNV activity is high in Los Angeles County. Also consider testing patients who are experiencing a nonspecific illness compatible with WNV fever.

WNV Symptom Table

Testing Information
Laboratory diagnosis is usually done by testing serum or cerebrospinal fluid (CSF) for WNV-specific IgM antibodies or viral detection using polymerase chain reaction (PCR). These tests are available at many commercial and public health laboratories.

In LA County from May to November, the DPH Public Health Laboratory (PHL) provides WNV-IgM serum antibody testing for suspect cases as well as for confirmation of ambiguous serum test results. WNV-IgM testing on CSF is available through the Viral and Rickettsial Diseases Laboratory (VRDL) at California Department of Public Health, and can be arranged through PHL. Additional serological and molecular testing for WNV is available at VRDL. PHL does not charge the submitter for these services. Testing at PHL from December to April requires consultation with the ACDC program (213-240-7941).

A standard laboratory submittal form must be completed and accompany the specimen(s). Each specimen must be labeled with the patient name and a second identifier (date of birth or medical record number), date of collection, and specimen type. Include a copy of previous test results and any pertinent patient history with the specimen including onset date. Send specimens by courier or overnight shipper using the appropriate transport conditions for the specimen type. Ship packages Monday-Thursday to avoid weekend deliveries. Frozen specimens should be shipped on dry ice.

WNV Testing Table

**Note regarding negative WNV-IgM:
  • WNV-IgM antibodies are usually detectable 3 to 8 days after onset of illness. If specimens were collected within 8 days of symptom onset false-negatives are possible. In early presentations, PCR testing can be ordered with serology. Alternatively, in highly suspect cases with negative WNV-IgM, repeating serology on a later sample will confirm diagnosis.
  • Consider SLEV infection if WNV testing is negative and there is no other likely etiology.

Saint Louis Encephalitis Testing
Saint Louis encephalitis virus (SLEV) has recently re-emerged in LAC and California. XX. Like WNV infection, SLEV infection is usually mild or asymptomatic but can cause severe neurologic illness, especially in the elderly. SLEV are transmitted by the same mosquitoes as WNV. Providers should consider SLEV infection in their differential diagnosis if WNV testing is negative and there is no other likely etiology. Serum serologic testing for SLEV is offered at commercial laboratories and at LAC PHL.

Human WNV and SLEV infections are reportable in California. Reporting of cases guides the DPH and the LAC mosquito abatement districts to target mosquito abatement services, surveillance activities and health education. The California Code of Regulations, section 2500, require providers to report all positive acute laboratory findings and clinical cases of WNV and SLEV infection to the patientís local public health department within one working day.

All cases of acute encephalitis and meningitis regardless of etiology are also reportable within one working day. A standard Confidential Morbidity Report (CMR) can be used to file a report; the CMR may be faxed to the DPH Morbidity Unit at (888) 397-3778. You may also report cases by telephone during normal business hours from 8:00 a.m. to 5:00 p.m. to (888) 397-3993. For cases among residents of the cities of Long Beach or Pasadena, please contact their local health departments.

Information for Medical Providers and Infection Control Practitioners

Additional Resources

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