Flawed herpes testing leads to many false positives — and needless suffering

Herpes is a lifelong infection, but Lauren had it only for six tumultuous months. Or rather, she believed she did, after a request for sexually transmitted disease testing returned a positive result. But after weeks of Googling, chatting with members of online herpes forums, and reading scientific papers, she asked for a different test, which eventually confirmed her suspicion — her herpes diagnosis was wrong.

In the six months that passed between the tests, the mistake led her to keep a romance at bay and left her anxiously patrolling her health.“Every tingle I would get in my leg or any kind of itch down there would just set me off,” sending her into a new flurry of research, she said. “And that was just to try to calm my own anxiety, but it would only really make it worse.”

Genital herpes, predominantly caused by herpes simplex virus type 2, is a sexually transmitted disease that’s very common — 1 in 6 people aged 14 to 49 in the United States have HSV-2, and this number goes up with age. Most of these people, however, don’t have obvious symptoms and wouldn’t know they were carriers without blood tests.

But blood tests can be highly unreliable. The kind of test used to diagnose Lauren, an IgM test, has long been rejected by the Centers for Disease Control and Prevention but is still used by some clinicians. Meanwhile, the CDC and the US Preventive Services Task Force concur that the most widely available herpes test, called HerpeSelect, should not be used to screen asymptomatic people because of its high risk of false positives: Up to 1 in 2 positive tests could be false, according to the USPSTF’s most recent guidelines.

That high failure rate isn’t, however, always communicated to patients. Online forums abound with stories like Lauren’s, of people who request herpes tests alongside those of other STDs and are shellshocked by the results. Some doctors discourage the testing or simply don’t include it in a standard STD panel without having the conversation. But no data exists on herpes screening rates, according to Kimberly Workowski, lead author of the CDC’s STD treatment guidelines — so it’s difficult to say how many people could be living with the misdiagnosis.

Testing pitfalls

Next to the meandering waterways connecting Puget Sound to Seattle’s Lake Washington is the only laboratory in the world that offers to the public the Western blot, the gold standard test for herpes. The University of Washington Clinical Virology Laboratory provides the test to patients across the country, a practice it began over a decade ago when it realized the more common tests were prone to false positives.

The problem, said Christine Johnston, a physician and researcher at the lab, is “low-positive” results of antibodies to HSV-2. The cutoff for a positive result on the HerpeSelect test, manufactured by Quest Diagnostics, is 1.1. A 2005 study published in the journal BioMed Central Infectious Disease found that index values above 3.5 yielded over 90 percent accuracy — but scores between 1.1 and 3.5 had around a 50 percent chance of being wrong.

What’s more, scores falling just above the 1.1 cutoff had an almost 90 percent chance of being wrong.

When tests fall between 1.1 and 3.5, more testing is necessary, said Johnston. This recommendation is also noted in the 2015 CDC Sexually Transmitted Diseases Treatment Guidelines. But some patients will never be referred for a second test.

“I think most clinicians are unaware and perhaps labs don’t have this available and/or it is not straightforward to order,” Johnston said of second-step tests.

But while her facility’s Western blot is considered highly accurate, it is expensive and cumbersome to perform. Each test costs over $200 and the University of Washington is the only lab that provides it.

Other confirmatory tests also exist, for instance Biokit’s HSV-2 Rapid Test and Quest’s own HSV-2 IgG Inhibition assay. The latter, which adds only $4 to the price of the HerpeSelect test, performed well in a study conducted over a decade ago. Rick Pesano, the medical director for infectious disease at Quest, believes that with more awareness, the test could stand in for the Western blot. But the test was not mentioned in the USPSTF guidelines because it still has not been evaluated in asymptomatic individuals, according to Cindy Feltner, associate director of the RTI-UNC Evidence-based Practice Center, who helped prepare the science review for USPSTF.

“We need better diagnostic testing. That is where we are stuck at this point,” said Johnston. “We don’t have a good test that’s inexpensive, high throughput, and reliable.”

Finding out the hard way

No good data exist on how often patients with questionable positive results are actually re-tested. Until the 2015 update, CDC herpes testing guidelines had no mention of confirmatory testing for low-positive results, said Johnston. So patients often discovered the option not through their doctors, but through searching the web and reading online herpes forums.

That was the experience of Bryan, a 40-year-old man who lives in Indiana, who wrongly believed he had herpes for about two months in 2011. The misunderstanding actually put him at higher risk, he said: During those months he considered joining the hundreds of thousands of Americans on dating sites for herpes-positive people. Exclusively dating people with herpes would have increased his likelihood of contracting the virus.

The experience of YT, a 33-year-old mom who has suffered from frequent herpes symptoms over the last year, shows another side of the testing breakdown. She believes she was given HSV by a partner who didn’t realize herpes wasn’t included in his previous STD tests, she told STAT. Having herpes has caused her significant emotional trauma, and has driven her to permanently swear off dating. Had her partner known his true status, she wonders if her story would have been different.

These kinds of stories come out in anguished postings on internet forums and in dozens of confused calls to the UW lab each week, where research coordinator Matt Seymour says some desperate patients call over and over again, unable to get the answers they need from their doctors.

“People call and say, ‘I just don’t know what’s going on,’” he said. “We’ve almost become de facto counselors.”

In the absence of answers

Herpes tests aren’t the only ones with a risk of false positive results. False positives can occur for any test that diagnoses viral infection based on antibodies, i.e., your body’s immune reaction, rather than direct detection of the virus. For similar diagnostics like HIV and hepatitis C testing, protocols automatically call for a second test that directly detects the virus whenever an antibody test comes back positive, said Paul Swenson, laboratory director in the department of public health of King County, Washington. Herpes, however, is a particularly challenging infection to directly test for, because the virus spends most of its time hiding in nerves. Swab tests can sometimes detect the virus during outbreaks, but this isn’t an option for people without symptoms. Thus even the Western blot relies on antibodies, and may give indeterminate results to a small number of people.

But two steps of antibody testing are still more reliable than one step; today’s diagnostics for Lyme disease and syphilis are a two-step antibody testing approach, said Dr. Edward Hook, a medical epidemiologist specializing in STI screening and prevention at the University of Alabama, Birmingham, who questioned why such a standardized two-step approach hasn’t taken firm hold for herpes.

“Some research has shown that two-step testing … might improve the specificity — that is avoid false positive results for the blood test — which would be a great thing because these diagnoses create great anxiety and concern for people,” he said. In a commentary accompanying the USPSTF guidelines, Hook expressed disappointment that herpes testing had barely improved over the past decade.

“There is no perfect test but there are ways to reduce the inaccuracies and reduce the number of equivocal results and those are actively used in other diseases,” he said in an interview with STAT. “But they haven’t been used very aggressively for the purpose of herpes.”

In the absence of sure-fire test advances, education and a lessening stigma surrounding herpes might help, not only by reducing test-related confusion, but potentially by bringing discussion of the virus out into the mainstream, said Hook.

“There’s no major herpes advocacy group,” he said. “People call attention to diseases that they suffer from, but people with herpes don’t feel they can call attention to it. And that creates a lot of suffering.”