STI Quarterly

FDA approves new test for chlamydia/gonorrhea

The Food and Drug Administration (FDA) has given clearance to Cepheid of Sunnyvale, CA, to market its Xpert CT/NG test. Running on the company's GeneXpert Systems, Xpert CT/NG is a qualitative in vitro molecular diagnostic test for the detection and differentiation of Chlamydia trachomatis and Neisseria gonorrhoeae. The test began shipping in January 2013, says Jared Tipton, Cepheid's senior director of corporate communications.

The Cepheid Xpert CT/GC test is not like any other point of care (POC) test available in the United States, says Edward Hook, III, MD, professor and director of the Division of Infectious Diseases in the Department of Medicine at the University of Alabama at Birmingham. The test performs as well as the most widely used nucleic acid amplification tests available, says Hook.

"These tests are far, far more accurate than currently available POC tests whose sensitivities compared to nucleic acid amplification tests are in the range of 50% or less," states Hook. "Thus, while the Cepheid test takes a bit longer than most POC tests — about 90 versus 30 minutes to provide results — it is far more accurate."

The Cepheid Xpert CT/GC test is designed so that it can be used in a clinic laboratory, rather than needing to have specimens shipped to a distant laboratory for processing, observes Hook. "It really represents a potentially major step for getting accurate test results back to patients in a timely fashion," he notes.

Getting faster results might help stem the rising tide of chlamydial and gonorrhea infections. According to newly released information from the Centers of Disease Control and Prevention (CDC), a total of 1.4 million cases of Chlamydia trachomatis infection were reported in 2011, the largest number of cases ever reported to CDC for any condition.1

In 2011, gonorrhea rates rose 4.0%, with a total of 321,849 cases of gonorrhea reported in the United States, corresponding to a rate of 104.2 cases per 100,000 population.2 This upsurge is concerning, as it marks a second year of increases after 2006-2009, when rates reached the lowest level since national reporting began.

Look at the test

How does the new test differ from other available diagnostics in the United States?

The tests are not batch-based, so results are available on-demand, says Tipton. This feature makes it suitable for testing and managing patients in emergency department settings, he notes. It also serves as a valuable tool for evaluation of patients with possible pelvic inflammatory disease (PID), Tipton adds.

The test is designed to avoid false positives, says Tipton. It has received regulatory clearance for all female direct specimens, including urine, self-collected vaginal, and cervical swabs, as well as male urine, states Tipton.

The FDA has categorized the Xpert CT/NG test as "moderately complex" under the Clinical Laboratory Improvement Amendments (CLIA). CLIA regulations are based on the complexity of the test method, Test methods are categorized into three levels of complexity: waived, moderate, and high. To run moderately complex tests, labs must meet requirements for quality control, quality assurance, proficiency testing, and personnel. The molecular CT/NG test is the first of its kind to be categorized as moderately complex, according to Cepheid.

The moderate complexity classification of the Xpert CT/NG test is hailed as a "breakthrough" for sexual health and sexually transmitted disease (STD) prevention, said Jeffrey Klausner, MD, MPH, professor of medicine at the University of California, Los Angeles David Geffen School of Medicine, in a statement issued by Cepheid. The large number of moderate complexity point-of-care laboratories that exist in U.S. hospitals and clinics now can offer rapid, highly accurate, and private same-day STD testing, noted Klausner.

"Public health officials need to work with providers to increase the availability of [such] tests," said Klausner. "Faster STD detection and treatment could go a long way in stemming the continued epidemic of STDs in the United States."

Data to emerge

Science also is eyeing the test for use with rectal swabs, as there are no commercially available approved molecular assays for the detection of Chlamydia trachomatis and Neisseria gonorrhoeae in rectal swabs.

A recent study looked at using the Cepheid GeneXpert CT/NG assay with the GenProbe Aptima Combo2 assay, using 409 rectal swabs. Using Aptima as the gold standard, the sensitivity, specificity, positive and negative predictive values of GeneXpert for the detection of C. trachomatis and N. gonorrhoeae were 86%, 99.2%, 92.5%, 98.4% and 91.1%, 100%, 100%, 98.6%, respectively. Despite significantly diluting samples prior to GeneXpert testing, the assay performed well with excellent specificity, researchers note.2


  1. Centers for Disease Control and Prevention. Sexually Transmitted Disease Surveillance 2011. Atlanta: U.S. Department of Health and Human Services; 2012.
  2. Goldenberg SD, Finn J, Sedudzi E, et al. Performance of the GeneXpert CT/NG assay compared to that of the Aptima AC2 assay for detection of rectal Chlamydia trachomatis and Neisseria gonorrhoeae by use of residual Aptima samples. J Clin Microbiol 2012; 50(12):3,867-3,869.