Mycoplasma genitalium (MG) is a lesser-known but increasingly recognized sexually transmitted infection (STI) caused by a bacterium. The organism often spreads quietly because many infected people experience no symptoms, allowing the infection to circulate undetected. As testing for this bacterium becomes more routine, medical professionals are gaining a clearer understanding of its prevalence and public health implications. This article clarifies the nature of this STI and addresses common questions regarding its transmission routes, particularly concerning oral sex.
Understanding Mycoplasma Genitalium
Mycoplasma genitalium (MG) is a bacterium that colonizes the mucous membranes of the urinary and genital tracts. MG is unique because it lacks a cell wall, which significantly impacts its biology and treatment. This absence means that common antibiotics, such as penicillin, which target cell wall construction, are ineffective against it.
The bacterium causes non-gonococcal urethritis (NGU) in men and cervicitis in women. MG prevalence rates are often comparable to, and sometimes exceed, that of Neisseria gonorrhoeae (gonorrhea) in high-risk populations. Since the infection is frequently asymptomatic, it can persist in the urogenital tract, increasing the likelihood of transmission to sexual partners.
Transmission Risk, Focusing on Oral Sex
The primary method of transmission for Mycoplasma genitalium is through sexual contact, particularly unprotected vaginal or anal intercourse. The infection spreads readily through the exchange of genital fluids or direct contact between genital mucous membranes. Up to half of the partners of people diagnosed with MG may also test positive, demonstrating its high transmissibility during genital contact.
Transmission through oral sex is possible, though it appears to be a less efficient route compared to genital-to-genital contact. The organism primarily targets the urogenital tract, but it can establish an infection in the throat, known as pharyngeal infection. One study estimated that new oropharyngeal infections accounted for a small percentage of overall new MG infections, suggesting that the throat is not a common primary site for the bacterium.
The prevalence of MG in the pharynx is low, estimated at around 1% in certain high-risk populations. Despite the lower colonization rate in the throat, cases of genital MG infection have been strongly linked to recent receptive oral sex in the absence of other sexual activities. This evidence indicates that Mycoplasma genitalium can be transmitted between the throat and the genitals during oral sexual contact.
Recognizing Symptoms and Potential Complications
The majority of people infected with Mycoplasma genitalium will not experience any noticeable symptoms. When symptoms do occur, they typically manifest as inflammation of the urethra (urethritis) in both men and women, often appearing one to three weeks after exposure. In people with a penis, symptoms can include a watery or mucoid discharge from the urethra and a burning sensation during urination.
For people with a cervix, the infection can cause cervicitis (inflammation of the cervix) or urethritis. Common symptoms in this population include unusual vaginal discharge, bleeding between menstrual periods, or bleeding after sexual intercourse. Inflammation can also lead to pain in the lower abdomen or pelvis.
If left untreated, MG infection can lead to serious long-term complications, particularly in women. MG is a recognized cause of Pelvic Inflammatory Disease (PID), which is an infection of the reproductive organs. PID can result in scarring of the fallopian tubes, increasing the risk of ectopic pregnancy and potentially leading to infertility. In men, untreated MG can cause inflammation of the epididymis (epididymitis) or prostate (prostatitis), causing pain in the testicles or surrounding areas.
Testing, Treatment, and Prevention Strategies
Diagnosing Mycoplasma genitalium requires specialized laboratory techniques because the bacterium grows very slowly and cannot be detected by standard bacterial cultures. The preferred method is a Nucleic Acid Amplification Test (NAAT), which detects the organism’s genetic material in samples. These tests are typically performed using first-catch urine samples or swabs taken from the cervix, urethra, or rectum.
Treatment for MG relies on specific antibiotics. The standard approach is often a two-stage therapy, beginning with a short course of doxycycline followed by a macrolide antibiotic, such as azithromycin, or a fluoroquinolone like moxifloxacin. This sequenced approach is intended to reduce the bacterial load and combat antibiotic resistance.
Antibiotic resistance is a concern with Mycoplasma genitalium, particularly to macrolide antibiotics, with resistance rates reaching 40% to over 68% in some areas. Due to this high resistance rate, single-dose azithromycin regimens are no longer recommended as they can promote further resistance. Safer sexual practices, such as the correct and consistent use of condoms during vaginal, anal, and oral sex, remain the most effective methods for reducing the risk of transmission.