Available from the CDC, this assay is a nucleic acid test (NAT) that qualitatively detects and differentiates the RNA from dengue, chikungunya, and Zika viruses in serum and CSF. It can also detect Zika virus RNA in urine and amniotic fluid. The test is designed to simultaneously test for the presence of the three viruses using a single sample. In the case of urine or CSF specimens, the CDC requires that the specimen be collected alongside a patient-matched serum specimen. Testing should be done on individuals meeting the CDC's Zika virus clinical criteria (eg, clinical signs and symptoms associated with Zika virus infection) and/or CDC Zika virus epidemiological criteria (eg, history of residence in or travel to a geographic region with active Zika transmission at the time of travel).
The Trioplex rRT-PCR test does not have a standard FDA approval. However, the FDA has authorized its use under the EUA status. Trioplex rRT-PCR assay includes primers and dual-labeled probes. The assay uses a reverse transcription step producing cDNA from RNA present in the sample. The probe binds to the target DNA between the two unlabeled PCR primers. There are virus-specific probes for the three viruses and during the PCR extension process, the polymerase extends the unlabeled primers using the template strand as a guide. The rRT-PCR instrumentation detects the fluorescence and with each cycle of the PCR, there is an increase in fluorescence that is proportional to the amount of target nucleic acid present.
The assay can be used for the identification of the Zika virus RNA (as well as dengue and chikungunya virus RNAs) during the acute phase of infection and typically up to 14 days following the onset of symptoms. The Trioplex rRT-PCR has been designed to minimize the likelihood of false positive test results. Cross-reactivity of any of the components of the test resulting in false positive results is typically not expected.
The Trioplex rRT-PCR is only intended for use by trained laboratory personnel who are proficient in performing rRT-PCR assays and it is only for use under the FDA's EUA guidelines. Moreover, laboratories performing the Trioplex rRT-PCR test are required to report all results to the appropriate public health authorities. Within the United States and its territories, results must be reported to CDC.
To summarize, here are key points regarding the Trioplex rRT-PCR test:
- A positive test result for the Zika virus indicates that the Zika virus RNA was detected in the specimen and indicates a current infection by the Zika virus. Laboratories are required to report all results to the appropriate public health authorities. (Within the United States and its territories, results must be reported to the CDC.
- Likewise, a positive test for dengue or chikungunya virus indicates that RNA from dengue and/or chikungunya was detected in the specimen and suggests a current infection with that virus.
- However, with any positive test result, the result should always be considered in the context of clinical observations and epidemiologic data in making a final diagnosis and patient management decisions.
- A negative test for Zika virus, dengue virus and/or chikungunya virus in the specimen means that RNA from Zika virus, dengue virus and/or chikungunya virus is not present in the specimen at the detection level of the assay. Although a negative result likely indicates no active infection, it must be noted that a negative result for one or more of these viruses does not rule out infection with the virus(s) and should not be used as the sole basis for treatment or other patient management decisions.
- A negative test for the Zika virus can occur in Zika infections, particularly if testing was conducted more than seven days after the onset of symptoms or in asymptomatic individuals. For CSF, amniotic fluid, and urine, it is especially important to note that these are not the primary diagnostic specimen types. Negative results in these specimen types do not necessarily mean that an individual is not infected. When negative results are obtained for these specimen types, then it becomes important to compare the result for the patient-matched serum specimen.
- The test is designed to minimize the likelihood of false positive test results. Cross-reactivity of any of the components of the test resulting in false positive results is not expected.
