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
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.
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. Given
immunological cross reactivity between WNV and
Saint Louis Encephalitis (SLEV), serologic
specimens positive for WNV and SLEV are routinely sent to VDRL for
confirmatory testing of both viruses. Information on testing for
SLEV is available
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).
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.
**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.
Reporting 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