Zika Tests in Texas Don’t Always Match Up

Congenital Zika syndrome testing needs to integrate clinical findings and epidemiologic history to render an accurate diagnosis

couple pregnant wife in field

Making a diagnosis of congenital Zika syndrome is challenging, despite the availability of testing resources in the United States.

Since January 2016, there have been 5,335 travel-associated cases reported in the United States. Additionally, 227 locally transmitted cases of infection with the Zika virus were reported in southern Florida and the Brownsville, Texas area.

A total of 2,364 pregnant women (972 completed pregnancies), with laboratory evidence of Zika virus infection in the USA, have been reported to the Centers for Disease Control and Prevention (CDC); the Zika-related birth defect risk among these women has been estimated to be 1 in 10 women.

Texas has reported 492 individuals to the CDC’s National Zika Pregnancy Registry.

As of February 23, two travel-related  Zika cases have been reported in Williamson County during 2018.

A recent study conducted in Brownsville, Texas, showed that Zika testing on expecting mothers during pregnancy, and the lab tests on their babies, did not match up.

This study identified 18 women exposed to Zika virus during pregnancy. These women were confirmed with supportive serologic or molecular test results indicating Zika virus or flavivirus infection.

And, two infants from these women, who had spent time in Mexico during their pregnancies, were evaluated for microcephaly during prenatal ultrasound. Results of neuroimaging performed prenatally for both infants was consistent with the presence and degree of microcephaly observed postnatally.

The first case-patient had maternal laboratory findings of probable flavivirus infection that was not identified until the third trimester. The first IgM screening (at 28 weeks’ gestation) might have shown a false-negative result, or the infection might have occurred later.

However, even without definitive evidence of maternal Zika virus infection at the time of delivery, the infant showed a positive result for Zika IgM in serum, and a subsequent placental test showed a positive result, which confirmed maternal infection.

The maternal diagnosis for case-patient 2 was confirmed with positive PCR results for serum at 23 weeks’ gestation.

However, despite this newborn displaying more severe features of congenital Zika syndrome postnatally (redundant scalp skin, bilateral upper arm arthrogryposis, smaller head size, and extrapyramidal symptoms), results of serum testing for Zika virus infection were negative.

In conclusion, the results for these 2 case-patients indicate the complexity and challenges of screening and diagnostic testing for congenital Zika syndrome and illustrate the need for clinical findings and epidemiologic history.

The testing limitations identified in this study illustrate that the spectrum of congenital Zika syndrome cannot be fully assessed until further postnatal assessment and highlights the need for advanced neuroimaging.

These researchers are advising other healthcare providers to have a high index of suspicion for congenital Zika syndrome for at-risk populations on the basis of current limitations of testing.

The leader of this study, Dr. Ashley J. Howard, is a physician and member of the South Texas Zika Task Force Team, Driscoll Children’s Hospital, Corpus Christi, TX., where both babies were evaluated and treated.

All authors of this study contributed equally and did not disclose any conflicts of interest: Ashley Howard, John Visintine, Jaime Fergie, and Miguel Deleon.

Separately an external quality assessment of 15 laboratories offering Zika diagnostic tests, using a new Zika virus standard, found 73% showed limited sensitivity and specificity, and the viral load estimates varied significantly.

The Texas Department of State Health Services (DSHS) top priority is to protect pregnant women from the risks associated with Zika virus infection during pregnancy.

Additionally, DHSH is recommending routine Zika virus testing for pregnant women who live in the Brownsville, TX area. This nine-county area is at a higher risk of Zika spreading by mosquitoes because of its climate and geography.

Reports out of Mexico show local Zika transmission continues to occur in some states and communities on the Mexican side of the border.

Routine testing provides important information to women about their pregnancies,” said DSHS Commissioner Dr. John Hellerstedt.

“It also increases the opportunity for public health to identify infections before Zika establishes itself in Texas so we can respond quickly.”