Molecular diagnostic test for Zika in Brazil not always reliable, study finds

A study from scientists at the Charité Universitätsmedizin Berlin found that almost two-thirds of all molecular diagnostic tests for the Zika virus in Brazil showed false-positive or false-negative results.

Almost all cases of Zika-associated malformations in newborns have been reported from Brazil.

Fifteen laboratories in seven Brazilian states, including the country’s most severely affected regions, participated in the study.

Each laboratory received twelve samples, which they investigated by means of the standard polymerase chain reaction (PCR) methods used in the laboratory. The laboratories did not know the contents of the individual samples. Zika-positive and Zika-negative samples were included along with samples that contained related viruses in order to test the specificity of the results.

Approximately one-third of the laboratories attained perfect results while approximately two-thirds of demonstrated partially incorrect results.

False-negative results showed insufficient test sensitivity and were unable to detect the existing viruses. False-positive results, which the scientists deem to be particularly critical, suggested contaminations or incorrect handling of the tests.

Additionally, viral load estimations, which describe the estimated amount of viral RNA in the blood or urine, showed varying results across the laboratories.

The researchers noted that assessments of Zika diagnostics in European laboratories showed similar results.

The researchers suggested further investments in reliable diagnostics and combining molecular tests with serological tests, which detect the antibodies developed by an infected person.

The researchers have scheduled further investigations with laboratory directors from the study.

“We need continuous global quality control for Zika virus diagnostics,” Professor Felix Drexler, who conducts Zika research at the Charité in Berlin, said.