Officials at a Washington D.C. public health lab confirmed to ABC News that they are retesting hundreds of samples from people in the area for Zika virus over concerns about the accuracy of the original test results.
Already, samples taken from two pregnant women, who originally tested negative for the virus, have now tested positive for likely Zika infection.
The District of Columbia Department of Forensic Sciences Public Health Laboratory has tested hundreds of people, mainly pregnant women, for the Zika virus since last year.
Yesterday, officials from the lab announced that after identifying "technical issues" with the Zika tests in December and a subsequent review of the tests, they would be retesting hundreds of specimens for signs of the virus collected during the second half of last year.
A spokesperson for the lab clarified to ABC News that "calculation and formulation errors" led to officials stopping and reviewing the Zika tests.
In total, 409 specimens that originally tested negative, including 294 from pregnant women, have been sent for retesting. The specimens from pregnant women were sent to the U.S. Centers for Disease Control and Prevention (CDC) and those from men and non-pregnant women were sent to public health labs approved by the CDC. It often takes two to three weeks to receive test results that could indicate a likely Zika infection. Currently, two of 62 samples that were sent to the CDC for additional testing, and then further confirmation testing, were positive for antibodies that would indicate a possible Zika infection.
The test looks for antibodies that indicate a current or past infection from a flavivirus, a family of viruses that includes Zika. The CDC is treating the patients who tested positive as though they tested positive for the Zika virus out of caution and for monitoring.
Currently, only specimens obtained between July 14, 2016 and December 14, 2016 will be reexamined, since those collected before that date were already tested by the CDC.
Dr. Christopher Zahn, vice president of practice activities for The American College of Obstetricians and Gynecologists (ACOG), called the testing issue a "very unfortunate situation" and said it is critical that patients get updated results quickly in case they need to get extra prenatal or post-partum care.
"The CDC has prioritized these lab retests and, as they are completed, it is critical that patients are informed of the updated results so they can follow-up appropriately based on current clinical recommendations," Zahn said in a statement. "ACOG and the CDC have been in contact and continue to consult and collaborate and will issue any additional necessary information."
The issue should serve as a reminder that "Zika is still a very serious public health crisis," he said, and that the public, as well as doctors and health officials, should remain vigilant.
"ACOG will continue to work closely with obstetric providers and offer the most up-to-date clinical guidance," he added.
Lab officials said they expect to have all retested sample results back in the next four weeks.
Zika infection in adults often has mild symptoms such as fever, rash, joint pain and conjunctivitis, according to the CDC, and approximately one in five people infected with the virus shows symptoms. Severe complications from Zika that require hospitalization are rare, and most people are over the worst of the symptoms after a week, according to the CDC.