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| Jonathan Zenilman and Charlotte Gaydos in the lab, testing the sensitivity of STD screens |
Sexually transmitted diseases like chlamydia and gonorrhea are insidious. Not only do they result in a higher risk of HIV infection and pelvic inflammatory disease, a serious infection of the fallopian tubes that can cause infertility in women, but they often come with no telltale signs. Many patients who do suspect they have an STD avoid testing because of anxiety about an invasive test or fear of being pegged promiscuous. And people who don’t get treated infect their partners, who also don’t get treated. The result? A “silent epidemic” of 15 million new STD cases – 4 million for chlamydia alone – in the United States each year.
“Gonorrhea and chlamydia are highly prevalent in urban areas, but most patients are asymptomatic,” says Jonathan Zenilman, M.D. “We need public health screening initiatives because a lot of people will be missed if we wait till symptoms appear.”
That’s why Zenilman and colleagues like Charlotte Gaydos, Dr.P.H., in Infectious Diseases are developing and testing less invasive screens, like nucleic acid amplification testing, or NAAT. While conventional testing requires a swab sample of cells from the cervix or urethra, which then has to be “cultured” in a lab for the presence of organisms, NAAT uses only a urine sample from which to directly test genomic nucleic acids, or DNA. While there are several types of amplification tests, including polymerase chain reaction (PCR) or ligase chain reaction (LCR), they all work under the same principle.
“You’re not looking for the organism itself, but parts of the organism’s genomic DNA,” Zenilman says. “Amplification enormously enhances the sensitivity of infectious microorganisms.”
So much so that amplification testing is not only increasing detection and treatment through easily self-obtained specimens at health fairs and schools, but also setting the gold standard for STD screening, replacing tissue cultures. “Because we’re looking at DNA,” Zenilman says, “the number of false-negatives and false-positives is extremely low.”
Not only that, amplification tests themselves are more sensitive than older DNA hybridization assays, notes Gaydos, whose lab is conducting clinical trials on many assay types of amplified tests for FDA clearance. While the old nonamplified, non-culture assays for chlamydia screening were 60 to 70 percent sensitive, she says, the new amplification tests are picking up 90-95 percent of the infections – so sensitive that they can be used to detect chlamydia in urine. That means a pelvic exam and a physician to collect the cervical specimen for testing chlamydia and gonorrhea are no longer required, allowing more women to be tested faster and more accurately.
“This has meant a huge shift from one-patient, one-doctor screening,” Gaydos says. “Now we’re able to screen 300 women at a time.”