Hundreds of Blood Samples Retested for Zika Due to False Negative Results

Two women who previously tested negative for Zika virus have now been lab-confirmed to be infected with “an unspecified flavivirus.”

In mid-December 2016, the District of Columbia (DC) Department of Forensic Sciences Public Health Laboratory (DC-PHL) discovered that all Zika virus diagnostic tests completed at the lab were coming back negative, and they made the decision to retest all of the serology specimens out of caution. Accurate Zika testing is imperative because of the many neurological effects rendered by congenital Zika infection. This is not the first time that a Zika test has yielded false results. In Late December 2016, the FDA announced that Zika tests conducted by LabCorp were yielding false positives.

In an official statement, DC-PHL reported that prior to July 14, 2016, all Zika virus diagnostic tests were conducted by the Centers for Disease Control and Prevention (CDC), and so those results are accurate. However, serum specimens tested between July 14, 2016 and December 14, 2016 using the Zika MAC-ELISA test may have yielded false negatives. The DC-PHL attributes the results to technical issues which they report do “not constitute any cause for alarm from the general public, and will not affect the District of Columbia Department of Health’s (DOH) management of probable or confirmed cases of Zika Virus Disease and infection.” According to a CDC spokesperson, these false negatives were yielded due to lab technicians skipping an imperative step in testing.

According to the DC-PHL, all of the specimens collected from pregnant women from December 14, 2016 onward have been sent to the CDC to be retested, with the remainder of the specimens are being tested in other public health laboratories. A total of 409 specimens will be retested; 294 of the specimens were collected from pregnant women. The DC-PHL has already started obtaining re-testing results from the CDC for 62 specimens. Specimens from two pregnant women who previously tested negative for Zika virus infection have come back positive for a flavivirus infection, which “for epidemiological purposes… are treated as positive for Zika.” Lab results for all other specimens are expected to reach the DC-PHL within 3 to 4 weeks.

The DC-PHL reports that, “If any results are found to be discordant from the original result obtained by DC-PHL, someone from the DC-PHL will immediately contact the submitter via phone and an amended report will be faxed. If a Zika serology result is found to be positive, the CDC or PHL will conduct the required confirmatory test.” The DC-PHL will not reach out to patients directly, but will, instead, contact healthcare providers.

For the women who test positive, the DC DOH will continue to follow up on pregnancy progress, and will recommend “increased frequency of ultrasounds.” The DOH will follow the CDC’s recommendations for testing “around time of delivery,” and the neurological development of those infants who develop complications associated with congenital Zika infection will be monitored for 1 year by their pediatrician, the results of which should be sent to the DOH. The DOH will notify healthcare providers of infants born to mothers whose retested specimens collected during pregnancy come back positive, so as to “arrange for testing and start standard follow-up with chart review to obtain past information.

The DOH will not follow up with those who tested negative in follow-up testing.