Mycoplasma genitalium

Overview

Mycoplasma genitalium (MG) is a sexually transmitted infection (STI) caused by the Mycoplasma genitalium bacteria.

Mycoplasma genitalium, the smallest known self-replicating bacterium currently, is increasingly the cause of non-gonococcal urethritis (NGU) in men and an increasingly recognised cause of cervicitis and pelvic inflammatory disease (PID) in women. It is a member of the Mycoplasmataceae family and Mollicutes class of bacteria. It is not visible on Gram-stain as it lacks a cell wall. Isolating M. genitalium is extremely challenging as it is a fastidious organism and may require more than one month to grow.

M. genitalium has been isolated from multiple tissue sites but its association with clinical disease appears to be limited to the urogenital tract. Studies in both male and female non-human primates, in which genital infection developed following urogenital inoculation of M. genitalium, demonstrate its pathogenicity. M. genitalium can persist for months or years in infected individuals.

Disease epidemiology

Available evidence showed that the summary prevalence was 1.3% in countries with higher levels of development, and 3.9% in countries with lower levels.

The lack of a cell wall renders M. genitalium resistant to antibiotics which target cell wall synthesis, such as penicillins and other beta-lactams. M. genitalium is generally susceptible in vitro to the macrolides (azithromycin more than erythromycin and clarithromycin), fluoroquinolones, tetracyclines, and clindamycin, although resistance is a growing issue.

Azithromycin has at least hundredfold more activity against this organism than the tetracyclines or most fluoroquinolones. However, strains of M. genitalium with resistance to azithromycin are increasingly reported following the use of single dose azithromycin in patients with non-gonococcal urethritis (NGU). In addition, reports of mutations in M. genitalium genes parC and gyrA, which are associated with fluoroquinolone resistance, have also surfaced.

There are currently no commercially available resistance tests in Singapore for M. genitalium.

Pathogen(s)

Mycoplasma genitalium.

Transmission

MG is transmitted through vaginal and anal intercourse with an infected individual. Researchers are still determining whether sex partners can spreadMG through oral sex.

Incubation period: Undefined.

Infectious period: Uncertain.

Clinical features

MG causes symptomatic and asymptomatic urethritis among men. When present, the typical symptoms of MG-urethritis include:

• Dysuria

• Urethral pruritus

• Purulent or mucopurulent urethral discharge

Among women, MG may cause cervicitis and pelvic inflammatory disease (PID), though individuals with cervicitis due to MG often are asymptomatic. When present, symptoms associated with MG cervicitis include:

• Vaginal discharge

• Vaginal itching

• Dysuria

• Pelvic discomfort

If untreated, PID may lead to:

• Formation of scar tissue that blocks fallopian tubes

• Ectopic pregnancy

• Infertility

• Long-term pelvic/abdominal pain

Risk factors

Risk factors include:

• Unprotected sex with an infected person

• Having multiple sex partners

• Inconsistent condom use if the relationship is not monogamous

• History or current presence of other STIs

Diagnosis

In the clinical setting, the microbiological diagnosis of M. genitalium is infrequently made because of the absence of commercially available, FDA-cleared diagnostic tests. However, if available, the diagnosis of M. genitalium infection may be made through detection of the organism using nucleic acid amplification tests (NAAT). The preferred specimens are a first-void urine sample in men/women and a cervical swab in women.

NAATs are the only clinically useful method of detecting M. genitalium but are not widely available locally; the DSC clinic provides a PCR test with a turnaround of seven working days. There are no standardised serological tests for M. genitalium.

Clinical suspicion of infection by M. genitalium should be high, and treatment can be given empirically even before laboratory confirmation. The approach to therapy of M. genitalium depends on the timing of presentation, the availability of M. genitalium PCR testing, and the treatment history. Treatment for M. genitalium can be considered in patients with NGU or MPC with a negative chlamydial PCR who continue to have symptoms and signs.

Treatment and management

Empiric treatment for urethritis, cervicitis, and PID includes therapy for C. trachomatis with doxycycline or azithromycin. Both agents have activity against M. genitalium, although clinical evidence suggests that azithromycin is superior to doxycycline. However high rates (50%) of macrolide resistance and fluoroquinolone mutations (20%) in M. genitalium have been reported.

Recommended regimens if macrolide resistant, resistance testing not available, or failed macrolide treatment:

• Doxycycline 100mg orally 2 times a day, for 7 days followed by moxifloxacin 400mg orally daily for 7 days

Recommended regimens if macrolide sensitive:

• Doxycycline 100mg orally 2 times a day, for 7 days followed by azithromycin 1g orally STAT then 500mg orally daily for 3 days

Recommended regimens if failed macrolide and fluoroquinolone treatment:

• Minocycline 100mg orally 2 times a day, for 14 days;

• Doxycycline 100mg orally 2 times a day, for 10 days plus pristinamycin 1g 3 times a day, for 10 days; or

• Pristinamycin 1g orally 4 times a day, for 10 days.

Recommended regimens for complicated infection (PID/epididymo-orchitis):

• Moxifloxacin 400mg orally daily for 14 days

Precaution, prevention, and control

Prevention of MG:

• Not having sex

• Consistent and correct use of condoms when engaging in sexual activity

• Limit the number of sex partners and

• Get tested for STIs regularly

Management of sexual contacts:

Although there are no guidelines for partner referral and treatment, it is reasonable to screen all sexual partners of laboratory-confirmed cases of M. genitalium and treat if positive. If screening of sexual partners of index patients with confirmed M. genitalium is not possible, treat M. genitalium empirically, based on evidence of its sexual transmission. Although the incubation period of this pathogen remains undefined, screening should target sexual partners within the past 60 days.

Notification

MG is not a notifiable disease. Please refer to the Infectious Disease Notification for more information.

Resources

Refer to Department of Sexually Transmitted Infections Control website for more information about MG.