Health Alert
RECOMMENDATIONS FOR SELECTING ZIKA VIRUS TESTS AND INTERPRETING RESULTS OF ZIKA VIRUS TESTING

Summary

The Delaware Division of Public Health (DPH) is issuing this health advisory to advise health care providers of the need to carefully choose testing modality and properly interpret the results of Zika virus testing based on time from symptoms onset.

Background

Zika virus is a flavivirus transmitted primarily by the bite of infected Aedes mosquitoes. In addition, sexual, in utero, and perinatal transmission have been documented.

Globally, Zika virus transmission by mosquitoes has been reported in 50 countries and territories. In the continental U.S., as of July 27, 2016, the vast majority of cases of mosquito-borne Zika infection have been travel related. However, the state of Florida has confirmed local mosquito transmission in 15 cases of Zika virus infection that occurred in non-travelers within a one-mile radius north of Miami. In Delaware, of 144 individuals tested for Zika virus as of July 27, 2016, 10 are confirmed cases and all were travel related.

Ordering/Interpreting Zika Results

Testing for Zika virus infection using real-time reverse-transcription polymerase chain reaction (rRT-PCR) molecular assays is now available in several commercial (non-government run) laboratories. At this time, commercial laboratories are not offering serology testing (Zika IgM Enyme-Linked Immunosorbent assay- ELISA). Both rRT-PCR and Zika-ELISA are available at the Delaware Public Health Laboratory.

This information is important in interpreting results because rRT-PCR methodology is indicated for serum samples collected seven days or less and urine samples collected 14 days or less after symptom onset. After seven to 14 days, the level of virus circulating in the blood (and present in the urine) declines significantly.

As a result, testing done with rRT-PCR on serum and urine more than seven days and 14 days respectively after symptom onset might result in false-negatives in individuals who actually have Zika.

As such, the Centers for Disease Control and Prevention (CDC) recommends testing using rRT-PCR for serum samples collected fewer than seven days and urine samples collected fewer than 14 days after symptom onset (or last possible exposure) and that specimens collected from patients more than 14 days after symptom onset should also have serology testing (ELISA) performed.

A positive rRT-PCR test is confirmatory of Zika virus infection and these cases do not need to be referred for further testing. However, a negative rRT-PCR result does not exclude Zika virus infection and serologic testing by ELISA for Zika IgM antibody should be done.

Recommendations/Reporting

If a health care provider receives a negative rRT-PCR result in a person with relevant travel or sexual exposure, they should contact the DPH Office of Infectious Disease Epidemiology at 888-295-5156 or 302-744-4990 to arrange for serology testing (ELISA) at the public health laboratory. ELISA is able to reliably detect Zika virus infection two to 12 weeks after symptom onset.

Contacting DPH

Providers are encouraged to call the DPH for any guidance needed in selecting the appropriate test to order for their patient or to arrange for Zika virus testing, coordinate specimen collection, or to report any suspect case of Zika virus infection or pregnant woman with potential exposure to Zika virus. Contact the DPH Office of Infectious Disease Epidemiology at 888-295-5156 or 302-744-4990.

Additional information

• CDC – Diagnostic Testing: http://www.cdc.gov/zika/hc-providers/diagnostic.html
• CDC – State and Local Public Health Laboratories: http://www.cdc.gov/zika/state-labs/index.html

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