CDC HEALTH UPDATE



CDC Recommendations for Subsequent Zika IgM Antibody Testing
 
Summary
Testing for Zika virus infection using real-time reverse-transcription polymerase chain reaction (rRT-PCR)
molecular assays is now commercially available. When requesting Zika rRT-PCR testing from a
commercial laboratory, providers should be aware that commercial laboratories performing rRT-PCR
currently do not also offer Zika IgM enzyme-linked immunosorbent assay (ELISA) or confirmatory
serologic testing (plaque reduction neutralization test, or PRNT). Therefore, if possible, providers should
store a serum aliquot for subsequent Zika IgM ELISA testing if the rRT-PCR assay is negative. Otherwise,
collection of an additional serum sample may be necessary
.
Recommendations
  • rRT-PCR (molecular) testing should be performed for patients possibly exposed to Zika virus who have symptoms consistent with Zika virus infection
  • Providers who request molecular testing for Zika virus infection from a commercial testing laboratory are advised to retain and store in a refrigerator (2-8°C) an aliquot of the patient’s serum for subsequent Zika IgM ELISA testing if the rRT-PCR is negative
  • For specimens that are rRT-PCR negative from the commercial laboratory and no stored serum specimen is available, another serum specimen should be collected within 12 weeks of symptom onset for Zika IgM ELISA testing
  • Appropriate samples for molecular testing are serum samples collected <7 days and urine samples collected <14 days after symptom onset. Urine should always be collected with a patient-matched serum specimen.
Background
Molecular assays for detection of Zika virus RNA are now commercially available under Emergency Use
Authorizations (EUAs) issued by the Food and Drug Administration (FDA). CDC recommends molecular
testing using rRT-PCR for serum samples collected <7 days and urine samples collected <14 days after
symptom onset. A positive rRT-PCR test is confirmation of Zika virus infection. However, because of the
decline in the level of viremia over time and possible inaccuracy in reporting of dates of illness onset, a
negative rRT-PCR result does not exclude Zika virus infection. In such cases, CDC recommends
serologic testing by ELISA for Zika IgM antibody.

Currently, commercial laboratories that offer rRT-PCR testing do not provide Zika IgM ELISA testing with
PRNT confirmation and have no routine process to forward specimens to another testing laboratory.
Therefore, when requesting Zika rRT-PCR testing from a commercial laboratory, providers should retain
an aliquot of the serum for Zika IgM ELISA testing if the rRT-PCR testing is negative. Blood should be
collected and processed per routine guidelines (collected in a serum separator tube with serum aliquots
transferred to new vials), and one of the serum aliquots should be stored in a refrigerator (2-8°C) until it is
known if additional IgM testing is indicated. If a serum aliquot cannot be stored or is not available, but
further testing is indicated, a new blood sample should be collected. Serum samples for IgM testing
should be collected from patients within 12 weeks of symptom onset. Providers should contact their local
health department to discuss IgM testing of stored or newly collected serum from patients who are rRTPCR
negative.

For More Information
The Centers for Disease Control and Prevention (CDC) protects people's health and safety by preventing and
controlling diseases and injuries; enhances health decisions by providing credible information on critical health
issues; and promotes healthy living through strong partnerships with local, national, and international
organizations.
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