July 26, 2017
Interpreting Results
Because of the decreasing prevalence of Zika virus in many areas of the world, CDC is alerting healthcare and public health partners of a likely increase in the rate of false-positive results in the initial testing completed at reference laboratories and state health departments (IgM testing results). In light of this development, it is very important that all samples testing presumptive positive and equivocal be sent to CDC for confirmatory testing (be aware that it may take up to a month to get confirmatory results back from CDC).
All presumptive positive and equivocal samples identified at the State Hygienic Laboratory have and will continue to be sent to the CDC for confirmatory testing.
If providers chose to submit samples to reference laboratories for Zika virus testing and receive presumptive positive or equivocal results, please contact IDPH by calling 800-362-2736 to ensure that the specimens are promptly forwarded to CDC for confirmatory testing.
In addition, the length of time in which IgM antibodies persist at detectable levels in Zika infected persons is highly variable. In some persons, antibodies are not detectable beyond 12 weeks post infection, but in others antibody persist well beyond that length of time.
Therefore, for in persons who seek care >12 weeks after symptom onset or exposure (if asymptomatic), a negative result does not rule out an infection because IgM antibody levels decline over time (and PCR will not detect virus that long after acute infection).
Conversely, Zika virus IgM antibodies can persist beyond 12 weeks post infection in some infected persons. Therefore, in persons who previously resided in or who have multiple dates of travel to Zika areas, results cannot always distinguish when the infection occurred (this has implications for pregnant women who previously resided in or had multiple dates of travel to Zika areas during and prior to their pregnancy).
Testing Recommendations
CDC continues to recommend Zika virus testing for all symptomatic persons (including persons who are pregnant and not pregnant) with possible Zika virus exposure through travel or sex.
CDC is no longer routinely recommending Zika virus testing for asymptomatic pregnant women with possible Zika virus exposure through travel or sex. Instead, CDC is recommending that patients and their healthcare providers work together to make decisions about testing and care plans based on patient preferences and val¬ues, clinical judgment, and a balanced assessment of risks and expected outcomes.
The State Hygienic Laboratory will test all symptomatic patients and asymptomatic pregnant women (if the patient and provider make the decision to test) with a history of Zika virus exposure. Iowa Healthcare Providers wishing to test their patients for Zika virus infection should continue to contact IDPH at 800-362-2736 to initiate sample submission.
Additional CDC Recommendations for Pregnant Women
All pregnant women in the United States should be screened for possible Zika virus exposure before and during the current pregnancy, at every prenatal care visit.
Pregnant women should not travel to any area with risk for Zika virus transmission (https://wwwnc.cdc.gov/travel/page/zika-travel-information).
Pregnant women whose sexual partners have traveled to or live in an area with Zika virus transmission should use condoms or abstain from sex for the duration of the pregnancy.
The updated guidance, including guidance for pregnant women with ongoing exposure (repeat travel to areas where Zika virus is transmitted) can be accessed at: https://www.cdc.gov/mmwr/volumes/66/wr/mm6629e1.htm?s_cid=mm6629e1_w
Infant Monitoring Recommendations
Infants born to mothers with possible Zika virus exposure during pregnancy who did not receive testing, who tested negative more than 12 weeks after exposure/symptom onset, or had additional exposures after testing occurred should receive a comprehensive physical examination, including standardized measurement of head circumference and newborn hearing screen, as part of routine pediatric care. Healthcare providers should also consider performing a head ultrasound, conducting an ophthalmologic assessment, and testing the infant for Zika virus infection.
For additional guidance on infant monitoring visit:
https://www.cdc.gov/mmwr/volumes/65/wr/mm6533e2.htm?s_cid=mm6533e2_w
Iowa Healthcare Providers wishing to test their patients for Zika virus infection should continue to contact IDPH at 800-362-2736 to initiate sample submission.
