Mycoplasma genitalium (MG) is a small bacterium and a recognized cause of sexually transmitted infection (STI). This organism lacks a cell wall, making it naturally resistant to many common antibiotics, such as penicillin. MG causes inflammation in the urethra (urethritis) in men and the cervix (cervicitis) in women. It is a common cause of persistent genital symptoms often mistaken for other STIs like chlamydia or gonorrhea.
The Incubation Period and Symptom Onset
The time it takes for Mycoplasma genitalium to cause noticeable symptoms after exposure is highly variable, known as the incubation period. This period can range widely from a few days to several weeks. While some sources report a range of one to three weeks, others suggest it can extend to four to eight weeks or even longer. The organism’s slow replication rate contributes to this extended timeline.
When symptoms do appear, they differ based on the anatomical site of the infection. For individuals with a penis, the infection commonly presents as urethritis. This involves a burning sensation during urination (dysuria) and a watery or mucous-like discharge.
In individuals with a vagina, symptoms are often focused on the cervix and may include abnormal vaginal discharge or discomfort during sexual intercourse. Cervicitis can also lead to bleeding between periods or post-coital bleeding. If the infection progresses upward, it can cause pelvic inflammatory disease (PID), which may present with lower abdominal or pelvic pain.
Understanding Asymptomatic Infection
The question of when MG “shows up” is complicated because the infection frequently remains entirely silent, or asymptomatic. A substantial proportion of infected individuals, particularly women, will not experience any noticeable symptoms. This lack of visible signs does not mean the infection is harmless; the organism is still present and actively colonizing the genital tract.
Even without symptoms, the infection remains highly transmissible to sexual partners. This silent nature is a primary reason why Mycoplasma genitalium continues to spread through populations. Studies confirm that a lack of discomfort is not a guarantee of being infection-free.
For individuals with a cervix, an asymptomatic MG infection can still lead to serious long-term reproductive health issues. The organism is associated with cervicitis and is a recognized cause of pelvic inflammatory disease (PID). PID can result in scarring of the fallopian tubes, increasing the risk of infertility and ectopic pregnancy.
Optimal Testing Windows for Detection
The biological incubation period for symptoms is distinct from the optimal window for laboratory detection. Diagnostic testing for Mycoplasma genitalium relies on Nucleic Acid Amplification Tests (NAATs), which detect the organism’s unique genetic material. For a NAAT to provide an accurate positive result, a sufficient number of bacteria must be present in the sample.
If testing is performed too soon after exposure, the bacterial population may not have replicated enough to be captured by the test, leading to a false negative result. This is a common error when testing for slow-growing organisms like MG. To minimize the chance of a false negative, medical guidelines recommend waiting a specific period after the last possible exposure.
The most reliable testing window for MG detection is generally considered to be two to three weeks post-exposure. This timeframe accounts for the slow replication cycle of the organism, allowing the bacterial load to reach detectable levels. Testing due to symptoms can happen immediately, as the presence of symptoms suggests the infection has reached a significant biological level.
If an individual is testing solely because of a known exposure without any symptoms, adhering to the two-to-three-week window is important for accuracy. The specific sample type, such as a first-catch urine sample for men or a vaginal swab for women, is also important for optimizing the NAAT’s ability to locate the organism.
Treatment Protocols and Follow-Up
Treatment for Mycoplasma genitalium is complicated by the bacterium’s increasing resistance to standard antibiotics. Strains resistant to macrolide antibiotics, such as azithromycin, are widespread. Because of this high rate of resistance, treatment protocols have evolved significantly beyond single-dose therapies.
Current guidelines often recommend a multi-step approach to maximize the chance of cure and reduce the selection of resistant strains. This typically begins with a course of doxycycline, which works to reduce the overall bacterial load. The second step then uses a different antibiotic, such as a prolonged course of azithromycin or moxifloxacin, depending on the suspected or confirmed macrolide resistance of the strain.
Completing the full course of prescribed medication exactly as directed is essential for eradicating the infection. Due to the high risk of treatment failure, a mandatory Test of Cure (TOC) is a necessary part of the protocol. This follow-up test confirms the elimination of the bacteria and should be performed approximately three to four weeks after the completion of the full antibiotic regimen. The TOC ensures that the infection has been successfully cleared and prevents the further spread of potentially resistant MG strains.