Weavewell

For reference only · Not medical advice

Sources include the CDC, FDA, HIV.gov, Australian STI Management Guidelines, PubMed-indexed research, and other linked references.

Infection

Mgen

Mycoplasma genitalium

Source evidence review: 2026-10-26. Source links are provided for transparency; guidance can change.

Stylized Mycoplasma genitalium: a flask-shaped cell with a terminal attachment tip and no cell wall. Not to scale; not diagnostic.

BACTERIAL STI / CARE & TRANSMISSION

Mycoplasma genitalium

Mgen is a treatable sexually transmitted bacterium. It often causes no symptoms; when it does, it can inflame the urethra or cervix and, less often, cause pelvic inflammatory disease. What helps is testing when there is a reason to, treatment chosen with resistance in mind, and follow-up with the clinic. [01][02][72]

Transmission risk

Risk by type of contact

Bottom line. Mgen can be transmitted without symptoms. Condoms are protective, but neither an exact protected-act probability nor the claim that transmission is virtually impossible is supported.

Type of contact

General

No barrier

Established sexually transmitted infection; no route-agnostic probability is defensible.*

  • No numeric estimate
  • Evidence: Low

Infected source at the contacted site; symptoms are not required.

Sources 1, 2

With a barrier

Condoms are considered protective, but no measured overall percentage or residual per-act probability is established.*

  • No numeric estimate
  • Evidence: Low

Correct coverage throughout relevant contact; uncovered acts remain separate.

Sources 2

Oral

No barrier

Oral transmission remains uncertain; throat detection and model fit do not establish a measured oral risk.*

  • No numeric estimate
  • Evidence: Low

Mouth-genital contact; do not equate detection of bacterial DNA with demonstrated infectiousness.

No validated mouth-to-genital versus genital-to-mouth estimates.

Sources 1, 3

With a barrier

An intact condom or dam should reduce covered fluid contact; Mgen-specific oral effectiveness has not been measured.*

  • No numeric estimate
  • Evidence: Low

Full oral-contact coverage; inference, not a trial result.

Sources 1, 2

Vaginal

No barrier

MODEL ONLY: male-to-female mean 18% (posterior range 7-30%); female-to-male 23% (8-30%). Not a measured condomless probability.*

  • Per act
  • Evidence: Medium

Birger 2017 heterosexual population model with a 1-30% per-act prior; barrier use not separately identified. Posterior ranges are reported model ranges, not 95% CIs. Do not use these as calibrated individual-risk constants.

Male-to-female approximates receptive vaginal; female-to-male insertive penile. Anatomical-route mapping is an inference.

Sources 4

With a barrier

Protective effect likely high; no numerical protected-act probability can be substantiated.*

  • No numeric estimate
  • Evidence: Low

Correct, intact condom throughout penetration. No justified percentage to apply to the model estimates.

Sources 2

Anal

No barrier

Anal transmission is recognized; available route models do not establish an empirically validated per-act probability.*

  • No numeric estimate
  • Evidence: Low

Source infection at urethral/rectal site; symptomatic or asymptomatic.

No validated receptive/insertive split.

Sources 1, 3

With a barrier

Condoms reduce covered mucosal/fluid exposure; absolute residual risk is not quantified.*

  • No numeric estimate
  • Evidence: Low

Intact condom used throughout anal penetration; no coverage assumed for rimming or other acts.

Sources 2

Kissing

No barrier

Kissing is not an established Mgen transmission route; hypothetical model routes are not proof.*

  • No numeric estimate
  • Evidence: Low

Ordinary and deep kissing considered separately from oral-genital sex.

Sources 1, 3

With a barrier

Not applicable: condoms and dental dams used for other acts do not protect a separate kissing exposure. No studied kissing-barrier effectiveness estimate.*

  • No numeric estimate
  • Evidence: Low

A separate oral barrier is not a validated kissing intervention; do not render this as a reduced-risk numerical cell.

Sources 1, 3

What changes the risk (4)
  • Treatment / resistance. MEDIUM: resistance-guided sequential treatment has reported cure rates above 90%; cure is not a numerical per-act prevention effect. Persistent infection after failed treatment remains relevant. Sources 1, 5
  • Updated resistance evidence. MEDIUM: UKHSA MARS 2025 sampled infections had 65.5% macrolide-resistance markers; this is resistance among selected infections, not infection prevalence or a transmission probability. Sources 6
  • Symptoms, ejaculation, menstruation and other STIs. LOW: no validated numerical multiplier identified for these modifiers. Absence of symptoms does not establish absence of transmissibility. Sources 1
  • Prevention drugs and vaccines. LOW: no established Mgen-specific vaccine, PrEP or PEP efficacy; bacterial-STI doxy-PEP trial benefits must not be transferred to Mgen. Sources 1, 7
Condoms and dental dams

ASHM describes protection as likely high; this is guideline judgment, not an Mgen-specific randomized efficacy percentage. No validated dental-dam effect size. Evidence: Low Sources 2

Sources for this risk profile (7)
  1. CDC CDC, 2021. Mycoplasma genitalium - STI Treatment Guidelines. cdc.gov
  2. ASHM Australian STI Contact Tracing Guidelines, current web guidance (accessed 2026-10-27). Mycoplasma genitalium. contacttracing.ashm.org.au
  3. Xu X et al. Scientific Reports, 2021. Modelling the multiple anatomical site transmission of Mycoplasma genitalium among men who have sex with men in Australia. DOI: 10.1038/s41598-021-90627-3. nature.com
  4. Birger R, Saunders J, Estcourt C, Sutton AJ, Mercer CH, Roberts T, White PJ Scientific Reports, 2017. Should we screen for the sexually-transmitted infection Mycoplasma genitalium? Evidence synthesis using a transmission-dynamic model. DOI: 10.1038/s41598-017-16302-8. pmc.ncbi.nlm.nih.gov
  5. Soni S et al.; BASHH International Journal of STD & AIDS, 2025. British Association for Sexual Health and HIV National guideline for the management of infection with Mycoplasma genitalium, 2025. DOI: 10.1177/09564624251359054. pubmed.ncbi.nlm.nih.gov
  6. UK Health Security Agency UKHSA, 2026. Mycoplasma genitalium antimicrobial resistance surveillance (MARS): report 2025. gov.uk
  7. Bachmann LH et al.; CDC MMWR Recommendations and Reports, 2024. CDC Clinical Guidelines on the Use of Doxycycline Postexposure Prophylaxis for Bacterial Sexually Transmitted Infection Prevention, United States, 2024. DOI: 10.15585/mmwr.rr7302a1. cdc.gov

* How to read these figures. Each is a published estimate under the conditions shown beside it, usually an untreated partner and a single act or partnership. It is not a prediction of your personal risk.

Evidence: High
Several prospective studies or a systematic review broadly agree.
Evidence: Medium
One or two studies, wide uncertainty, or a model.
Evidence: Low
Guideline judgment, case reports, or extrapolation.

Where no risk level is shown, the evidence cannot rank it. That is not the same as low.

Evidence reviewed through 2026-10-27. For reference only; not medical advice.

When to test after a possible exposure

No single well-validated post-exposure rule-out day. Do not substitute the incubation period or the post-treatment waiting interval.

When to be seen sooner. Symptoms, pelvic pain or a confirmed relevant exposure warrant clinical assessment rather than waiting for an arbitrary testing date.

  • Mgen NAAT, with resistance testing where available

    • No established window
    • Evidence: Low

    The reviewed guidelines do not define a universally reliable exposure-to-positive cutoff.

    Testing fits symptoms, or being an ongoing partner of someone with a confirmed result. Whether a one-time protected contact without symptoms should test differs between guidelines, including within Denmark; a clinic can help decide and can plan a repeat if an early result is negative.

    Specimens: First-pass urine; Vaginal swab; Other validated genital specimens; rectal specimen only when indicated

    Sources 1, 2

Early negatives, after treatment, and screening limits

An early negative result. An early negative does not establish that an exposure was too recent to transmit or that acquisition is excluded. There is no evidence-based automatic day-X clearance badge.

After treatment. Australian guidance: when test of cure is indicated, NAAT should not be taken earlier than 14-21 days after treatment completion. CDC does not require routine test of cure in asymptomatic people treated with a recommended regimen; its specified alternative regimen requires testing 21 days after completion. This clock starts after treatment, not after exposure.

Screening limits. Routine asymptomatic population screening is not recommended. Testing a relevant contact or evaluating persistent symptoms is a different question.

Kissing and body sites. Australian guidance does not recommend routine throat swabs for Mgen. A urine/genital result is not an all-site result; rectal testing is indication- and guideline-dependent. No kissing-specific screening clock is established.

Sources for testing guidance (2)
  1. CDC STI Treatment Guidelines. Mycoplasma genitalium. 2021. cdc.gov
  2. Australian STI Management Guidelines. Mycoplasma genitalium: testing sites and test of cure. Live guidance. sti.guidelines.org.au

Treatment

Treatment commonly uses doxycycline first, followed by an antibiotic selected for resistance and clinical circumstances. Repeated single-dose azithromycin is not an appropriate default. Penicillin and cephalosporins do not work because Mgen lacks a cell wall. Properly selected, resistance-guided regimens can cure more than 90%, but cure is not guaranteed. [01][02]

Actions

1. Get the right test. If testing is indicated, an Mgen-specific NAAT, ideally with resistance testing, is the useful test. Vaginal swabs or first-pass urine are common specimens. Throat swabs are not routinely recommended; rectal testing depends on symptoms, contact history and local guidance. [01][02]

2. Talk with ongoing partners. There is no universal lookback period for Mgen. Testing is usually offered to anyone with symptoms and to ongoing partners of someone with a confirmed result. Whether a single protected contact without symptoms should test differs between guidelines, including within Denmark, so a clinic can help each person decide; see Mgen: the decisions that matter. [01][02][03]

3. Prevent reinfection. Finish treatment and follow the clinic's advice about sex and partners. If a follow-up test is needed, it is timed rather than immediate: Australian guidance waits at least 14-21 days after treatment, and US recommendations differ. [01][02]

SCIENCE & CONTEXT

Mgen / the evidence

History

The organism was first isolated from men with urethritis and reported in 1981. That is a discovery date, not evidence that the infection began then. Molecular tests later made detection more practical; recognition of macrolide and fluoroquinolone resistance changed treatment from empirical single-drug therapy toward staged, resistance-guided care. No vaccine is available. [01][02][07]

Impact

Mgen attaches to mucosal cells and can cause inflammation even without symptoms. Burning when urinating, discharge, bleeding after sex, pelvic pain or rectal symptoms are worth having checked, though each has several possible causes. Mgen is linked with pelvic inflammatory disease; the long-term risk for someone without symptoms is uncertain. [01][02]

A positive result cannot date acquisition or identify a source. A negative result earlier in the year does not, by itself, distinguish later reinfection from an earlier missed or persistent infection. The specimen site, assay, timing and intervening contacts matter. [01][02]

Probability at a glance

Chance that at least one recent partner has Mgen, by number of partners in six months. This is not your chance of getting it.

Partners 6% scenario 16.6% scenario 23.5% scenario

1-2

6.0–11.6

16.6–30.4

23.5–41.5

3-5

16.9–26.6

42.0–59.7

55.2–73.8

6-10

31.0–46.1

66.3–83.7

80.0–93.1

11-20

49.4–71.0

86.4–97.3

94.7–99.5

The 6% scenario comes from one club sample; 16.6% and 23.5% come from selected US clinics, not from all party networks. [04][05]

In short: the more partners, the more likely it is that someone in a network has Mgen. Barriers, testing when there is a reason to, and treatment still change what happens, and these figures do not describe any particular community. See Mgen: the decisions that matter and Evidence, models and probability tables.