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
Email:acdc2@ph.lacounty.gov

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Acute Communicable Disease Control
(Back to Zika main page)
Zika Virus Testing and Diagnosis
This page contains information on Zika virus testing and reporting for suspect cases residing in Los Angeles County. It also contains information for notifying Public Health for special cases. If you need to report or consult on a case residing outside Los Angeles County, please search here for contact information of other California Health Departments.

Zika testing by PCR or serology (IgM) is available at commercial laboratories and can be ordered using regular clinical testing protocols. The Los Angeles County Public Health Laboratory (PHL) conducts confirmatory Zika virus testing as needed (see Zika Testing Using Commercial Laboratories below).

FINAL LAC West Nile Virus and Other Arboviral Diseases Report: February 2, 2018 (2-2-18)
LAC DPH Health Advisory: Updated California Zika Testing Guidelines and a Local Case of Sexually Transmitted Zika (1-4-18)

ON THIS PAGE:
INDICATIONS FOR ZIKA VIRUS TESTING
All Patients
Recommended:
  • Any symptomatic individual with recent possible exposure to Zika Possible exposure to Zika includes living in, or traveling to, or having unprotected sex with someone who lives in or traveled to an area with risk of Zika (Zika Locations HERE).
Not Recommended:
  • asymptomatic non-pregnant individuals
  • preconception screening

Pregnant Women
Recommended:
  • Symptomatic pregnant women with possible recent exposure to Zika
  • Asymptomatic pregnant women with ongoing exposure to Zika
  • Pregnant women with possible Zika exposure with prenatal ultrasound findings suggestive of birth defects potentially associated with Zika
May be considered for:
  • Asymptomatic pregnant women with recent possible exposure (but not ongoing exposure) based on risk assessment (not routinely recommended).

ZIKA INFECTION SCREENING QUESTIONS

Use the following questions:
  • Do you live in or frequently (daily or weekly) travel to an area with Zika risk?
  • (If pregnant) Have you traveled to an area with Zika during your pregnancy or just before you became pregnant (8 weeks before conception or 6 weeks before last menstrual period)?
  • Have you had sex without a condom (male or female) or without other barrier methods (i.e., dental dams) with a sexual partner(s) who live or travels to an area with Zika?
  • If YES to any of the above questions, ask for signs or symptoms of Zika (fever, rash, conjunctivitis, or joint pain) in the 12 weeks from time of last exposure.
Providers who suspect a case of Zika virus infection should obtain a relevant clinical history including previous dengue/chikungunya/West Nile virus infection, travel history, Japanese encephalitis virus/yellow fever/tickborne encephalitis vaccination history, as well as the results of relevant diagnostic tests, if performed (e.g., ultrasound imaging, TORCH (Toxoplasmosis, Rubella, Cytomegalovirus, and Herpes simplex virus) serology panel, West Nile virus serology, dengue serology, chikungunya serology).

WHEN TO CONSIDER LOCAL EXPOSURE

Because Los Angeles County is an area at increased risk for local transmission, a diagnosis of Zika should be considered if the patient meets ALL of the following criteria:
  • Lives or works in an area with documented Aedes aegypti mosquitoes (map of Aedes HERE)
  • Has a maculopapular rash AND at least one other symptom consistent with Zika (fever, joint pain, or conjunctivitis)
  • Is >18 years old (febrile rash illness frequently occurs in children associated with viral infection; not testing children will substantially improve the specificity of surveillance for Zika), and
  • No other diagnosis is identified that could cause the observed symptoms.
Clinicians who suspect Zika infection in a patient who has not traveled to a Zika-affected area should consult with Acute Communicable Disease Control: 213-240-7941.

TESTING PREGNANT WOMEN
1. For pregnant women with recent possible Zika virus exposure and symptoms of Zika virus disease:
Test for Zika virus concurrently with PCR (both serum and urine) and Zika virus IgM antibody testing as soon as possible through 12 weeks after symptom onset. If IgM result is non-negative (positive or equivocal), confirm with plaque reduction neutralization test (PRNT).

2. For asymptomatic pregnant women with ongoing possible Zika virus exposure:
  • Offer PCR testing at least three times during pregnancy (consider once per trimester), unless a previous test has been positive.
  • Consider Zika virus IgM testing during the 1st and 2nd trimesters. IgM is no longer routinely recommended as a positive result may not necessarily indicate infection during current pregnancy due to prolonged persistence of antibody.
  • Counsel pregnant women on the limitations of Zika IgM and PCR testing during each trimester (HANDOUT).

3. For asymptomatic pregnant women with recent possible Zika virus exposure (not ongoing):
Patients should be assessed carefully for factors that increase the likelihood of infection and testing should be requested based on shared patient-provider decision making. Routine testing is no longer recommended. Risk assessment should include consideration of:
  • Local Zika transmission at destination at time of travel
  • Duration of travel
  • Types of activities during travel (e.g., outdoor vs. indoor)
  • Known mosquito bites
  • Use of repellant or protective clothing
  • Housing conditions (e.g., no window screens or air conditioning)
  • Other family members with Zika diagnosis
  • Number of unprotected sexual exposures during travel
  • Blood transfusion or transplant in area with Zika (without reliable testing of blood supply for Zika at destination

4. For pregnant women with recent possible Zika virus exposure who have a fetus with prenatal ultrasound findings consistent with congenital Zika virus syndrome:
Maternal Zika virus PCR and IgM antibody testing should be performed.

5. Testing placental tissue specimens:
Placental testing from pregnancies with possible Zika virus exposure that result in live births can be considered on a case-by-case basis for diagnostic purposes when there is no definitive diagnosis of laboratory-confirmed Zika virus infection for symptomatic pregnant women and women with an infant born with possible Zika virus-associated birth defects. Placental or fetal tissue testing may be considered in other scenarios after CDPH has been consulted and received pre-approval from the CDC.

DETERMINING LABORATORY EVIDENCE OF A CONFIRMED RECENT ZIKA VIRUS INFECTION
Laboratory evidence of a confirmed recent Zika virus infection includes:
  • Positive PCR result on both serum and urine, regardless of IgM results.
  • Positive PCR result on either serum or urine, in conjunction with a positive Zika IgM.
  • Positive or equivocal Zika virus IgM test on serum with a positive titer for Zika virus (≥10) from PRNT together with negative PRNT titer (i.e., <10) for dengue virus.
Positive PCR result on either serum or urine, with negative Zika IgM may be suggestive of acute Zika infection. In this situation, repeat PCR testing should be performed on original serum sample and if positive again can be interpreted as evidence of recent Zika infection. If repeat PCR is negative, repeat serum Zika IgM testing should be obtained ≥ 2 weeks after exposure, specimen collection or symptom onset. See CDC Zika Test Result Interpretation Table HERE.

NEWBORN TESTING
Testing is recommended for infants:
  • born to mothers who have laboratory evidence of Zika virus infection during pregnancy
  • born to mothers who have travelled to a Zika risk area during pregnancy whose lab results are still pending, or
  • who have abnormal clinical findings suggestive of congenital Zika syndrome and a maternal epidemiologic link suggesting possible exposure during pregnancy, regardless of maternal test results.
NOTE: A Zika virus RNA NAT test should be performed on both infant serum and urine, and Zika virus immunoglobulin M (IgM) antibody should be performed on infant serum. Testing should be performed on specimens collected from infants within 2 days after birth; however, testing specimens collected within the first few weeks to months after birth may still be useful in the evaluation for possible congenital Zika virus infection.

Recommended laboratory testing for congenital Zika virus infection includes evaluation for Zika virus RNA in infant serum and urine and Zika virus IgM antibodies in serum. In addition, if cerebrospinal fluid (CSF) is obtained for other purposes, NAT and IgM antibody testing should be performed on CSF. Testing of cord blood is not recommended because it can yield false-positive and false-negative test results.

Diagnosis of congenital Zika virus infection is confirmed by a positive Zika virus NAT result. If Zika virus IgM antibodies are detected in the infant with a negative NAT, the infant is considered to have probable congenital Zika virus infection. If neither Zika virus RNA nor Zika IgM antibodies is detected on the appropriate specimens (e.g., serum or urine) obtained within the first few days after birth, congenital Zika virus infection is unlikely.

If the infant’s initial sample is IgM non-negative (non-negative serology terminology varies by assay and might include “positive,” “equivocal,” “presumptive positive,” or “possible positive”) and NAT negative, but PRNT was not performed on the mother’s sample, PRNT for Zika and dengue viruses should be performed on the infant’s initial sample if the test is appropriate given the setting. A negative Zika virus PRNT suggests that the infant’s Zika virus IgM test was a false positive.

PRNT cannot distinguish between maternal and infant antibodies in specimens collected from infants at or near birth; however, based on what is known about other congenital infections, maternal antibodies are expected to become undetectable by age 18 months and might become undetectable earlier. For infants whose initial sample is IgM non-negative and Zika virus neutralizing antibodies are detected on either the infant’s specimen at birth or the mother’s specimen, PRNT at age ≥18 months might help confirm or rule out congenital Zika virus infection. If PRNT is negative at age ≥18 months, congenital Zika virus infection is unlikely. For infants with clinical findings consistent with congenital Zika syndrome who have maternal laboratory evidence of possible Zika virus infection during pregnancy, PRNT at age ≥18 months could be considered if the infant testing results are negative (i.e., negative Zika virus NAT and IgM on infant serum and urine) or if the infant was not tested at birth.

Interpretation of serologic results has been described and published by the CDC HERE.

TESTING PARTNERS OF PREGNANT WOMEN
Public Health recommends Zika virus testing for any person (male or female) who has been exposed to Zika within the past 12 weeks and who has/had symptoms consistent with Zika illness (fever, arthralgia, rash, conjunctivitis).

Testing is also recommended for any person (male or female) who has/had symptoms consistent with Zika illness (fever, arthralgia, rash, conjunctivitis) within the past 12 weeks and who had unprotected sex (i.e., not using a condom) with a partner who lives in or traveled to an area with Zika transmission (including a US location with ongoing local Zika spread) during the 2 weeks before the onset of symptoms.

Testing of male partners who are asymptomatic can be done at commercial labs only.

TESTING CHALLENGES
Laboratory testing for Zika virus has limitations. Zika virus RNA is only transiently present in body fluids; thus, negative NAT does not rule out infection. Serologic testing is affected by timing of sample collection: a negative immunoglobulin M (IgM) serologic test result does not rule out infection because the serum specimen might have been collected before the development of IgM antibodies or after these antibodies have waned. Conversely, IgM antibodies might be detectable for months after the initial infection; for pregnant women, this can make it difficult to determine if infection occurred before or during a current pregnancy. In addition, cross-reactivity of the Zika virus IgM antibody tests with other flaviviruses can result in a false-positive test result, especially in persons previously infected with or vaccinated against a related flavivirus (e.g., dengue, yellow fever, and Japanese Encephalitis viruses), further complicating interpretation.

TESTING AT COMMERCIAL LABORATORIES
Zika IgM enzyme-linked immunosorbent assay (ELISA) and real-time reverse-transcription polymerase chain reaction (rRT-PCR) molecular assays are now available at commercial laboratories. Please submit your specimens to commercial laboratories for processing using your regular clinical testing protocol.

At this time, commercial laboratories do not have confirmatory serologic testing (plaque reduction neutralizing test or PRNT) that is recommended if IgM enzyme-linked immunosorbent assay (ELISA) is non-negative (non-negative serology includes positive, equivocal, presumptive positive, or possible positive). Confirmatory testing is not required if IgM ELISA is negative. Molecular testing on tissue samples, CSF, and amniotic fluid are not currently available at commercial laboratories. For this reason, if a commercial testing laboratory is used for testing, it is recommended that:

  • Providers retain and store in a refrigerator (2-8°C) an adequate number of blood specimens for patient's serum to perform subsequent PRNT confirmatory testing when needed.
  • Providers are familiar with the laboratory-developed/Emergency Use Authorized test performed at the commercial laboratory and corresponding specimen requirements, which may differ from that performed at Public Health Laboratories.
  • Providers assure that the commercial laboratory can perform PCR testing on both urine and serum specimens.

In general, serum specimens should be collected within 12 weeks of symptom onset or last potential exposure. For PCR testing, the serum and urine samples should be collected <14 days after symptom onset or last potential exposure. Urine should always be collected with a patient-matched serum specimen for rRT-PCR testing. A summary table for interpretation of Zika nucleic acid and antibody testing is available HERE.

Note: Facilities that do not have the capability to process and adequately store serum samples for subsequent antibody testing should contact PHL for assistance at 562-658-1330/1300.

If a commercial laboratory is used for Zika PCR and/or IgM enzyme-linked immunosorbent assay (ELISA) testing, providers must report all positive Zika tests by submitting a Confidential Morbidity Report.

The Los Angeles County PHL will continue to offer access to Zika and other related arbovirus testing services (see Testing at the Los Angeles County Public Health Laboratories (PHL) section below).

For additional information on commercial laboratory testing from CDC, see Health Update: Recommendations for Subsequent Zika IgM Antibody Testing (6/21/16).

TESTING AT THE LOS ANGELES COUNTY PUBLIC HEALTH LABORATORIES (PHL)
The PHL offers access to all recommended screening and confirmatory testing for Zika and related arboviral infections. Some of this testing is sent to the California State laboratory and/or CDC.

The Los Angeles County Zika Virus Testing and Report Form  must be completed for specimens to be processed. Failure to complete required fields on the requisition forms will result in specimen rejection or delayed testing. The form includes a two-page reporting and test requisition form as well as the specimen requirements and submission instructions found below. A separate test requisition form must be submitted for each specimen type. The Zika Virus Testing and Report Form available here.

Specimen Requirements for Zika Testing
Note: requested sample volumes are for adults.
Specimen Requirements for Zika Testing

* Specimens must be received within 24 hours of collection.
**Do not use glass vacutainer tube for blood collection. Do not use tubes that contain anti-coagulants.
***To optimize evaluation of possible Zika virus infection on fetal tissues, please provide both formalin-fixed and unfixed tissues. If it is not possible to provide both types of tissues, prioritize formalin-fixed tissues. For additional information regarding collection of fetal or infant tissues, please contact the Public Health Laboratories for guidance.

Instructions for Test Requests
Samples submitted with incomplete intake information, incomplete patient history, incomplete or discrepant patient sample identifiers and labeling information, or incomplete test request forms will not be tested.

Provider may be required to complete additional forms for receiving results by fax if not currently a client of the Los Angeles County PHL.

Convalescent serum or an additional serum sample may be requested depending on laboratory results.

  1. Download and complete the required information for Zika Virus Test Request Form. Separate testing forms (both pages 1 and 2) must accompany each specimen type.
  2. The following information must be included on the form:
    1. Facility/Submitter name, address, phone, and fax
    2. Requesting provider name (Last, First) and contact information to enable reporting of results
    3. Patient name or unique patient identifier
    4. Patient sex
    5. Patient date of birth
    6. Test(s) to be performed
    7. Specimen source
    8. Date and time of specimen collection
  3. If the patient or provider are unable to obtain phlebotomy services, contact the Los Angeles Acute Communicable Disease Control Program (ACDC) for assistance, approval, and referral to a Los Angeles County Public Health Clinic.
  4. Specimens must be labeled with the following information:
    1. Patient name (Last, First)
    2. Date of Birth
    3. Collection Date and Collection Time
Specimen Processing and Packaging
Proper storage and transport conditions preserve analyte integrity within the sample. Leaking specimens will also be rejected:
  • Clinics able to process specimens may centrifuge blood and transfer serum to a separate, sterile, labeled tube
  • Samples must be sent to the Los Angeles County PHL as soon as possible and within 24 hours of collection
  • Each specimen type must come with its own test request form
  • Each specimen must be packaged using individual biohazard specimen transport bags

Specimen Transport
Laboratory samples for Zika testing should not be sent directly to the California State Department of Public Health or the Centers for Disease Control.

Send samples to the Los Angeles County Public Health Laboratories (PHL) as soon as possible and within 24 hours of collection.

Los Angeles County Public Health Laboratories
12750 Erickson Avenue
Downey, CA 90242
Phone 562-658-1300
Fax 562-401-5999

Specimen transport conditions must be followed or sample will be rejected.

If a provider does not have access to courier services, PHL will help to arrange for sample pick up. Courier arrangements can be made by calling PHL Central Accessioning Unit at 562-658-1460.

 
 
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