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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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
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
FINAL LAC West
Nile Virus and Other Arboviral Diseases Report: February
LAC DPH Health Advisory: Updated California Zika Testing
Guidelines and a Local Case of Sexually Transmitted Zika
ON THIS PAGE:
Testing at the
Los Angeles County Public Health Laboratories (PHL)
INDICATIONS FOR ZIKA VIRUS TESTING
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
asymptomatic non-pregnant individuals
May be considered for:
Symptomatic pregnant women with possible recent exposure
Asymptomatic pregnant women with ongoing exposure to
Pregnant women with possible Zika exposure with prenatal
ultrasound findings suggestive of birth defects
potentially associated with Zika
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:
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,
simplex virus) serology panel, West Nile virus serology, dengue serology, chikungunya
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
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
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.
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:
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.
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
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
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
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
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.
Known mosquito bites
Use of repellant or protective clothing
Housing conditions (e.g., no window screens or air
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
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.
Testing placental tissue specimens:
DETERMINING LABORATORY EVIDENCE OF A
CONFIRMED RECENT ZIKA VIRUS INFECTION
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.
Laboratory evidence of a confirmed recent Zika 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
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.
Testing is recommended for infants:
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
born to mothers who have
laboratory evidence of Zika
virus infection during pregnancy
mothers who have travelled to a Zika risk area during
pregnancy whose lab results are still pending, or
abnormal clinical findings suggestive of congenital Zika
syndrome and a maternal epidemiologic link suggesting
possible exposure during pregnancy, regardless of
maternal test results.
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
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,
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.
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
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
requirements, which may differ
from that performed at Public
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
Note: Facilities that do
not have the capability to process and adequately store
serum samples for subsequent antibody testing should
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.
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
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)
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.
* 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
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
Specimen Processing and Packaging
- 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.
- The following information must be included on the form:
- Facility/Submitter name, address, phone, and fax
- Requesting provider name (Last, First) and contact information to enable
reporting of results
- Patient name or unique patient identifier
- Patient sex
- Patient date of birth
- Test(s) to be performed
- Specimen source
- Date and time of specimen collection
- 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.
- Specimens must be labeled with the following information:
- Patient name (Last, First)
- Date of Birth
- Collection Date and Collection Time
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,
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
Each specimen must be packaged using individual
biohazard specimen transport bags
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
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.