Mycoplasma genitalium

Introduction

Mycoplasma genitalium is a small bacterium with no cell wall, so traditional methods of Gram stain and culture cannot be used to detect and identify it. Nucleic acid amplification testing (NAAT) is recommended for detection of this organism. 

Clinical significance

M. genitalium has become a well-recognised cause of sexually transmitted infections worldwide and has been shown to cause urethritis, cervicitis and pelvic inflammatory disease (PID). Although the organism has been discovered at multiple anatomic sites, there is insufficient evidence that it is a primary cause of proctitis, and no evidence that it causes pharyngitis or epididymoorchitis. Asymptomatic infections can also occur, but the consequences are unclear.

Prevalence in Australia

The prevalence of M. genitalium infection in Australia varies depending on the clinical setting and population being tested. Overall, it is estimated to be around 1% in young adults (18-27 years old), but can be significantly higher in specific populations like men who have sex with men (MSM). Prevalence is also higher in individuals presenting with nongonococcal urethritis (NGU) (15-25%) and PID (up to 15%).

Antimicrobial resistance

Treatment of infection caused by this organism is challenging in an era of increasing antimicrobial resistance across multiple drug classes, and emerging resistance worldwide has become a concern. Azithromycin (macrolide) resistance exceeds 60% in Australia in the majority of cases and exceeds 80% in MSM. Fluoroquinolone resistance is also rising and approaching 20% in many urban settings, impacting on the efficacy of moxifloxacin. Moxifloxacin is not recommended for use in pregnancy or breastfeeding. 

Specimen collection

Clinical Labs recommends testing for M. genitalium on a first-pass urine sample or two dry swabs suitable for NAAT testing. Gel-containing transport media should not be used. Two swabs are required, one for the M. genitalium NAAT assay and one for macrolide resistance testing if M. genitalium is detected. If only one swab is received, macrolide resistance testing cannot be performed, and a further collection will be needed. If a urine sample is received, the sample can be split to accommodate both tests. However, the test sensitivity on urine is slightly less than on swabs.

Laboratory testing

Approved specimen types

Molecular tests are required to identify this organism and are approved for use on urine, endocervical, vaginal and urethral swabs. Throat swabs are not recommended, as pharyngeal infection is uncommon.

Indications for testing

Testing should be performed on patients with persistent or recurrent urethritis or cervicitis once chlamydia and gonorrhoea have been ruled out and symptoms persist despite therapy. Testing should also be performed on patients with PID or post-coital bleeding. Current sex partners of patients being treated for symptomatic M. genitalium infection should also be tested, even if they are asymptomatic.

Screening recommendations

Asymptomatic or routine screening for M. genitalium is not currently recommended due to lack of knowledge regarding its natural history, rising antimicrobial resistance and increasing complexities around access to effective treatments. 

Testing methodology at Clinical Labs

At Clinical Labs, testing is performed with the Aptima Mycoplasma genitalium assay. This assay is a highly sensitive rRNA-based NAAT that can detect very low levels of M. genitalium. It is much more sensitive than DNA-based assays, which may miss up to 40% of infections. The Aptima assay does not test for macrolide resistance, so positive specimens are referred to another laboratory to perform resistance testing. However, due to the difference in sensitivity between the rRNA assay and DNA assays, the results from the referral laboratory may come back negative. If this occurs, then a result cannot be obtained for macrolide resistance. 

Laboratory Testing and Diagnosis

• Clinicians should not routinely screen for M. genitalium in asymptomatic individuals.
• Clinicians should test for M. genitalium in individuals with persistent or recurrent urethritis or cervicitis.
• When testing is indicated, clinicians should use NAAT to diagnose M. genitalium infection, with resistance testing if available.

Treatment

Clinical Labs microbiologists recommend using standard resources such as the ASHM Health Treatment Guidelines and/or the Australian Therapeutic Guidelines: Antibiotic for determining whether treatment is required, and if so, which agents to use.

If a macrolide susceptibility result cannot be obtained by NAAT, then the best treatment regimen will depend on individual patient factors such as the presence or absence of symptoms, the possibility of reinfection, treatment(s) received so far and persistence/recurrence of PCR positivity. Complicated infections may require specialist referral. It is reasonable to assume macrolide resistance is present in infections persisting after failure of azithromycin, particularly in men who have sex with men, where macrolide resistance exceeds 80% in most urban settings in Australia.

Contact tracing is recommended for ongoing sex partners.

Test of cure

Perform test of cure 21 days after treatment is completed, and if symptoms persist or there is ongoing risk of reinfection. Testing earlier than 14 days may lead to false-positive results.

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