Primary Care Corner with Geoffrey Modest MD: Zika Virus Testing

By Dr. Geoffrey Modest

Zika virus testing: the CDC just published new guidance for testing for the Zika virus (see http://www.cdc.gov/mmwr/volumes/65/wr/mm6518e1.htm?s_cid=mm6518e1_w ):

Use real-time reverse transcription-polymerase chain reaction (rRT-PCR) on urine if <14 days after the onset of symptoms in patients with suspected Zika virus disease
Use rRT-PCR test on urine and on serum if <7 days after symptom onset
Any positive test result provides evidence of Zika infection

rRT-PCR is a rapid test and is highly specific
In most patients, the Zika virus RNA is not detected in the serum after the first week of illness
Recent report found the rRT-PCR to be positive in the urine for at least 2 weeks after onset of symptoms (in Florida study, from as early as 1st day of symptoms till as late as 20 days later)
The Florida study also found that of 66 cases, 61 (92%) had positive urine and 31 (47%) positive blood testing.
Within the first 5 days of symptoms, of 55 patients, 52(95%) had a positive urine test and 31 (56%) had a positive blood test
>5 days after symptoms, 9 (82%) had positive urine and none had positive serum
Of the 53 who had testing at multiple sites: 92% had positive urine, 81% positive saliva, and 51% positive serum

So, urine testing is by far the most sensitive overall, but there are occasional cases of Zika positive only on blood testing.

Persons with 2 or more of: rash, fever, arthalgias or conjunctivitis during or within 2 weeks of return from an area with Zika virus activity, or with a link to a Zika virus infected traveler (sexual partner, household contact, etc.)
For CDC guidance for women of reproductive age with possible Zika virus exposure, see http://www.cdc.gov/mmwr/volumes/65/wr/mm6512e2.htm

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