CDC Updates Guidelines on Laboratory Testing for Sexually Transmitted Infections

On July 22, the US Centers for Disease Control and Prevention (CDC) revised its guidelines for the diagnosis and treatment of sexually transmitted infections (STI), including with regard to how to test for certain kinds of infections. Here is an overview of what you need to know if STI testing is part of your laboratory’s portfolio.

The Diagnostic Challenge

The term “sexually transmitted infection” refers to a pathogen that causes infection through sexual contact (not to be confused with the term “sexually transmitted disease” (STD), which refers to a recognizable disease state that develops from an infection). In addition to increasing the risk of HIV transmission, STIs can have serious health effects, including human papillomavirus (HPV) which causes genital warts and is implicated in cancer of the cervix. Many STIs are asymptomatic or sub-clinical and thus go undiagnosed. But screening, especially of high-risk individuals, is effective in preventing STIs.

In 2015, the CDC made waves by issuing revised guidelines (Sexually Transmitted Diseases and Treatment Guidelines, 2015) recommending the use of nucleic acid amplification tests (NAATs) for use in screening high-risk populations for Trichomonas vaginalis and routine trichomonas. The updated guidelines build on those recommendations.

NAAT-Based Diagnosis of Mycoplasma Genitalium

Back in 2015, there was no US Food and Drug Administration-cleared molecular test for M. genitalium, which can take up to six months to grow in culture. Accordingly, the CDC said the bacterial infection could be suspected only in cases of persistent or recurrent urethritis, cervicitis, and pelvic inflammatory disease (PID). But in 2019, the FDA cleared Hologic’s Aptima assay for M. genitalium STI in men and women, a fact that the new guidance expressly mentions.

According to the new guidelines, men with recurrent Non-Gonococcal Urethritis (NGU) should be tested for M. genitalium using an FDA-cleared NAAT. Resistance testing should be performed if is available. Women with recurrent cervicitis should be tested for M. genitalium, and testing should be considered among women with PID. Testing should be accompanied with resistance testing, if it is available. However, the guidelines stop short of recommending screening of asymptomatic M. genitalium infection or extragenital testing for the infection.

The guidelines also highlight molecular assays available for diagnosis of T. vaginalis, including not only the Hologic Aptima test, but also Becton Dickinson’s (BD) ProbeTec and BD Max TV tests, Cepheid’s GeneXpert TV and Quidel’s Solana and AmpliVue TV tests. They also mention non-molecular tests, including Sekisui Diagnostics’ Osom trichomonas rapid test and BD’s Affirm VPIII assay.

Diagnosis of Gonorrhea Infections

As before, CDC recommends routine annual screening for N. gonorrhoeae and chlamydia for all sexually active females ages 25 or older. Extragenital gonorrhea screening (pharyngeal or rectal) can be considered for females on the basis of reported sexual behaviors and exposure, via shared clinical-decision between the patient and the provider, the guidelines add. However, CDC says there is insufficient evidence of efficacy or cost-effectiveness to recommend routine screening for N. gonorrhoeae among asymptomatic sexually active young males who have sex with females only. Screening for gonorrhea, including pharyngeal or rectal testing, should be offered to young men who have sex with males (YMSM) at least once a year. Annual chlamydia rectal, but not pharyngeal testing is also recommended for this population.

Gonorrhea detection using molecular tests is more sensitive than culture-based methods, the guidelines note, but sensitivity may vary by anatomical site. Patient-collected samples are “reasonable alternatives to provider-collected swabs for gonorrhea screening by NAAT.” The CDC also reiterates recent guidance that ceftriaxone alone be used to treat gonorrhea, rather than dual therapy with ceftriaxone and azithromycin, due to the emergence of azithromycin resistance.

Other Recommendations

Other notable CDC recommendations in the new STI guidelines:

• Clinical diagnosis for herpes simplex virus (HSV) testing should be confirmed by type-specific virologic testing using NAAT or culture for cases in which genital lesions are present;
• Type-specific serologic tests can be used to aid diagnosis of HSV infection in the absence of genital lesions. The CDC recommends two-step serologic testing for HSV;
• Universal hepatitis C (HCV) testing should be done at least once in a person’s lifetime via an initial antibody test, with positive results confirmed using an FDA-cleared HCV NAAT; and
• Sekisui Diagnostics’ Osom BV Blue point-of-care test may have utility for bacterial vaginosis (BV) but CooperSurgical’s FemExam Test Card is not a preferred method of diagnosis.

The new guidelines also mention commercially available quantitative multiplex PCR assays for BV by name, including:

• BD’s Max Vaginal Panel;
• Hologic’s Aptima BV;
• LabCorp’s NuSwab VG;
• Quest Diagnostics’ SureSwab BV; and
• Medical Diagnostic Laboratories’ OneSwab BV Panel PCR with Lactobacillus Profiling by qPCR.

The guidelines note that the BD and Hologic BV assays are FDA-cleared, while the other three are laboratory-developed tests.