The U.S. Food and Drug Administration (FDA) announced on May 23 that it had cleared the Aptima Combo 2 Assay and Xpert CT/NG to detect chlamydia and gonorrhea by using throat and rectum samples, potentially making it easier for physicians and public health programs to diagnose and treat sexually transmitted infections (STIs) that are often undertreated for lack of testing in those areas.
"Prior to today, there were no chlamydia or gonorrhea tests cleared for use on samples from the throat and rectum," said Tim Stenzel, M.D., Ph.D., director of the Office of In Vitro Diagnostics and Radiological Health in the FDA's Center for Devices and Radiological Health in the news release. "It is best for patients if both of these sexually transmitted infections are caught and treated right away, as significant complications can occur if left untreated. Today's clearances provide a mechanism for more easily diagnosing these infections."
Nucleic acid amplification tests (NAATs) are an industry standard for diagnostics but had not received FDA approval for these two specific sample sites until now. In the study of clinical data used by FDA to evaluate safety and efficacy, multiple commercially available NAATs were evaluated for detection accuracy of Neisseria gonorrhoeae and Chlamydia trachomatis from throat and rectal sites. The research, led by the Antibacterial Resistance Leadership Group and funded and supported by the National Institute of Allergy and Infectious Diseases, included more than 2,500 patients throughout the U.S. The Aptima Combo 2 Assay and Xpert CT/NG demonstrated the greatest efficacy and safety.
"A gigantic barrier to testing has now been cleared," said Barbara Wilgus, M.S.N., C.R.N.P., with the STD/HIV Prevention Training Center at Johns Hopkins.
These latest developments are crucial in detecting these STIs at the site of possible infection; for instance, in the case of anal or oral sex. A urine sample may not be as comprehensive in picking up the presence of chlamydia or gonorrhea if the urethra is not the infection site. With improved diagnostic tools like these, a swab can pinpoint N. gonorrhoeae or C. trachomatis infection directly at the extragenital site (i.e., the throat or rectum).
"Previously, in the absence of this clearance, individual labs would have to internally validate their ability to perform extragenital NAATs testing for gonorrhea and chlamydia," added Wilgus. "And while many larger labs did do this, many, many other labs did not have this capability, and many regions in the United States were not able to offer extragenital testing to patients even when providers knew of the benefits."
But questions remain about the cost of the tests, and whether or not they'll be covered by insurance plans.
"A problem with the test is they have been very expensive, and insurance won't cover a lot," said David Malebranche, M.D., M.P.H., with the Morehouse School of Medicine. "The FDA approval helps sometimes, but it takes a while for insurance to catch up. That is likely purposeful, so [insurance companies] can maximize their profits. That often happens. FDA approval lags behind the scientific findings. Insurance lags behind FDA approval."
But more screening of extragenital sites is definitely needed. The Centers for Disease Control and Prevention (CDC) has reported the fourth consecutive year of record-high rates for all STIs. There were an estimated 1.7 million cases of chlamydia infection and more than 500,000 cases of gonorrhea in the United States in 2017.Among gay, bisexual, and other men who have sex with men, more than 70% of extragenital gonorrhea and more than 85% of extragenital chlamydia infections go undetected if extragenital STI testing isn't used. One in 15 men who have sex with men who had rectal gonorrhea or chlamydia were diagnosed with HIV within a year in a 2013 study of data from New York City public STI clinics. Those with untreated rectal STIs have an even greater vulnerability to HIV infection.
Wilgus stressed that the new technology will be useful, providers will still need to be comfortable with talking to their patients about sex and suggesting STI screening.
"A comprehensive sexual health approach, including taking a thorough sexual history, and obtaining specimens from the patient at all sites of sexual activity, is hopefully unchanged," she said. "What this FDA clearance does change is access to the appropriate technology for testing, making it accessible to all. Providers needing to scale up their sexual health approach may feel more comfortable obtaining oral and rectal specimens with the knowledge that the testing itself yields an accurate result."