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    Guidance from CDC on Zika test results


    The Centers for Disease Control and Prevention (CDC) has issued new interim guidelines for interpretation of results of testing for Zika virus antibodies, which focus on a more conservative approach. The goal is to reduce the possibility of missing the diagnosis of either Zika or dengue virus infection.

    In the report, CDC cited recent evidence which suggests that a 4-fold higher titer by plaque reduction neutralization test (PRNT) may not discriminate between anti-Zika virus antibodies and cross-reacting antibodies in all individuals who have been previously infected with or vaccinated against a related flavivirus. (A PRNT using a 90% cutoff value with a titer ≥10 against Zika virus, together with negative PRNTs [i.e., <10] against other flaviviruses is confirmatory of recent infection with Zika.) PRNT may performed to confirm a diagnosis in cases in which immunoglobulin (Ig) M test results are positive, equivocal, or inconclusive. A positive real-time reverse transcription-polymerase chain reaction (rRT-PCR) result confirms Zika virus infection in individuals suspected to have Zika virus disease but a negative result does not exclude infection.

    More: CDC declares Zika virus teratogenic

    An enzyme-linked immunosorbent assay (ELISA) can be used to detect anti-Zika virus IgM antibodies in serum or cerebrospinal fluid but the Zika virus IgM ELISA may produce false-positive results because of false-positive results because of cross-reacting IgM antibodies related flaviviruses or nonspecific reactivity. PRNT measures virus-specific neutralizing antibody titers and should be performed against various related flaviviruses to rule out false-positive ELISA results.

    CDC recommends that all pregnant women with laboratory evidence of a recent Zika virus infection or flavivirus infection be evaluated and managed for possible adverse pregnancy outcomes and their cases reported to the appropriate Zika virus pregnancy registry. Patients whose serologic testing indicates recent flavivirus infection caused by either Zika or dengue virus should be clinically managed for both infections because they could be infected with either virus.  

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    Judith M. Orvos, ELS
    Judith M. Orvos, ELS, is a a BELS-certified medical writer and editor and an editorial consultant for Contemporary OB/GYN.
    Miranda Hester
    Ms. Hester is Content Specialist with Contemporary OB/GYN and Contemporary Pediatrics.


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