New Study Supports Expanded Testing for Gonorrhea and Chlamydia

NIAID Now | July 01, 2019

This scanning electron micrograph shows Neisseria gonorrhoeae bacteria, which can cause gonorrhea.

Credit: NIAID

A new study from the NIAID-funded Antibacterial Resistance Leadership Group (ARLG) found that two diagnostic tests accurately detected gonorrhea and chlamydia in samples from the pharynx (throat) and rectum. The findings informed the Food and Drug Administration’s (FDA) recent decision to approve the diagnostics for use in these extragenital sites. Now, the tests may be more readily available to clinics across the country. The findings were presented at ASM Microbe in San Francisco on June 23, 2019, by Sarah Doernberg, M.D., associate professor in the Division of Infectious Diseases at the University of California, San Francisco.


Previously, diagnostics for gonorrhea and chlamydia were approved in the U.S. for testing samples from the reproductive system and urinary system only. However, both gonorrhea and chlamydia can be found in the pharynx and rectum. People who are infected with gonorrhea and chlamydia often do not have symptoms and can unknowingly transmit the infections if left undetected. 


Gonorrhea and chlamydia are two of the most common sexually transmitted infections (STIs) in the United States. The Centers for Disease Control and Prevention estimates that there are approximately 820,000 new cases of gonorrhea and 2.86 million cases of chlamydia each year, primarily in young people ages 15 to 24.


Prompt, accurate diagnosis of STIs can reduce transmission, improve treatment outcomes, and prevent the spread of drug-resistant strains. Drug resistance is of particular concern for gonorrhea, which is rapidly developing resistance to available treatment options.


Recognizing the public health need for readily-available diagnostics for extragenital gonorrhea and chlamydia infections, the ARLG launched the MASTER GC study. The study evaluated how well the Aptima Combo 2 Assay from Hologic, Inc., and the Xpert CT/NG diagnostic from Cepheid, Inc., detected these infections in extragenital samples. The ARLG used an innovative “Master Protocol” study design, which allowed researchers to test multiple diagnostics from different manufacturers on each sample.  


The study, led by Jeffrey D Klausner, M.D., M.P.H. at the University of California, Los Angeles, enrolled nearly 2,600 adults seeking STI testing at nine clinics across the United States. Both symptomatic and asymptomatic participants enrolled in the trial. Clinicians collected pharynx and rectal swabs from consenting participants, and then investigators tested the samples with each diagnostic. Researchers concluded that the tests accurately identified extragenital chlamydia and gonorrhea infections.


The MASTER GC study provided the critical data needed for the recent FDA approvals, which made Aptima Combo 2 Assay and Xpert CT/NG the first diagnostics approved for extragenital testing for chlamydia and gonorrhea in the United States. ARLG experts anticipate the tests will fill a significant gap in the prevention and control of gonorrhea and chlamydia and expect the Master protocol trial design to have broad impact on diagnostic development. Testing several products using samples from the same patient can increase efficiency and reduce clinical study costs. This streamlined process could expedite the development of new and improved diagnostics not only for STIs but also other infectious diseases, including pneumonia, urinary tract infections, and bloodstream infections.

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