What is the Simplexa Test for Herpes?

Herpes Virus, artwork. David Mack/Science Photo Library/Getty Images

Until recently, there have been two primary types of tests that can be used to detect genital herpes infections. The first type of test is viral culture, which looks for the presence of live virus in active sores. It is a very powerful test, but it only works at very specific times in the cycle of infection -- when sores are not only present but the virus is still active. If a person goes to the doctor on the wrong day, it's very easy to get a false negative.


The second type of test is herpes blood tests, which look for the presence of antibodies against the herpes viruses. These tests are less dependent on a person being sampled at a particular time, as long as its been at least a month or two since the type of infection. However, there are enough accuracy concerns about the potential false positives and false negatives that many doctors aren't willing to provide these tests to their patients. The risks of these outcomes are low, but given the herpes stigma issues, they may not be low enough.

The Simplexa HSV 1 & 2 Direct molecular test  by Focus Diagnostics, which was approved by the FDA for testing cerebrospinal fluid in 2014 and genital swabs in 2015 is a different kind of test than either of the two mentioned above. It is, in some ways, more similar to the urine tests for chlamydia and gonorrhea that have been on the market for several years.

Instead of looking for live virus, or antibodies, it instead looks directly for viral DNA.

Like all other screening tests, the Simplexa tests isn't perfect. Estimates of its sensitivity (able to tell people when they do have HSV) and specificity (ability to tell people when they don't have HSV) are pretty good, but there is still a potential for false positives and false negatives.

Still, it is has the potential to fill a useful void in the screening regimen -- where sores may no longer have enough active virus to test positive in culture but it's too soon to rely on antibody testing.

Interesting Fact: The Simplexa HSV 1 & 2 test was initially developed as a test for cerebrospinal fluid, because in rare cases herpes can cause encephalitis -- a swelling of the brain. This swelling can also be caused by herpes zoster, the herpes virus responsible for causing chicken pox and shingles. There is also some preliminary data suggesting that herpes can cause mild cognitive impairments even in people who have never experienced encephalitis, but the nature of the study means the results need to be confirmed in a more detailed investigation.


Food and Drug Administration. FDA OKs Genital Swab Claim on Focus Diagnostics’ Simplexa System. FDA News. September 8, 2015. Accessed 9/19/15 at http://www.fdanews.com/articles/172955-fda-oks-genital-swab-claim-on-focus-diagnostics-simplexa-system

Fruchter E, Goldberg S, Fenchel D, Grotto I, Ginat K, Weiser M. The impact of Herpes simplex virus type 1 on cognitive impairments in young, healthy individuals - A historical prospective study. Schizophr Res. 2015 Sep 8. pii: S0920-9964(15)00465-X. doi: 10.1016/j.schres.2015.08.036.

Gitman MR, Ferguson D, Landry ML. Comparison of Simplexa HSV 1 & 2 PCR with culture, immunofluorescence, and laboratory-developed TaqMan PCR for detection of herpes simplex virus in swab specimens. J Clin Microbiol. 2013 Nov;51(11):3765-9. doi: 10.1128/JCM.01413-13

Grahn A, Studahl M. Varicella-zoster virus infections of the central nervous system - Prognosis, diagnostics and treatment. J Infect. 2015 Sep;71(3):281-93. doi: 10.1016/j.jinf.2015.06.004

Heaton PR, Espy MJ, Binnicker MJ. Evaluation of 2 multiplex real-time PCR assays for the detection of HSV-1/2 and Varicella zoster virus directly from clinical samples. Diagn Microbiol Infect Dis. 2015 Mar;81(3):169-70. doi: 10.1016/j.diagmicrobio.2014.11.012.

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