Mycoplasma genitalium (MG) is a common, often overlooked sexually transmitted infection (STI) affecting the urethra, cervix, and rectum. The bacteria frequently causes no noticeable symptoms, meaning many people are unaware they are infected and can unknowingly transmit it. When symptoms do occur, they include discharge or a burning sensation during urination. After completing antibiotics, patients often wonder about the possibility of the infection returning.
Recurrence Is Not Always Reinfection
A positive MG test after initial treatment does not necessarily mean a new infection has been acquired. Recurrence is typically the result of two distinct scenarios: treatment failure or reinfection. Differentiating these causes dictates the subsequent medical approach.
Treatment failure, or persistence, means the initial antibiotic regimen failed to eradicate all the bacteria, allowing remaining organisms to multiply. This persistence is often linked to the bacteria developing resistance to the drug used. Reinfection occurs when a patient clears the initial infection but acquires a new one from an untreated sexual partner.
Failure suggests the need for a different, usually stronger, antibiotic, while reinfection points to a breakdown in prevention or partner management. Clinicians must use both laboratory results and the patient’s recent sexual history to determine the most likely cause. For example, if a patient abstained from sex during and after treatment, a positive test strongly suggests treatment failure and persistence of the original strain.
The Role of Antibiotic Resistance
The primary reason for treatment failure is the rapid development of antibiotic resistance in MG. Since the bacteria lacks a cell wall, treatment options are limited primarily to macrolides and fluoroquinolones. The macrolide antibiotic azithromycin was historically a first-line treatment, but its effectiveness has sharply declined in many regions due to high rates of resistance.
Resistance develops when the bacteria undergo specific genetic changes, or mutations, that allow them to survive exposure to the drug. For azithromycin, resistance is commonly linked to mutations in the 23S ribosomal RNA gene, which is the target of the macrolide drug. Treatment failure rates with azithromycin have been reported to be substantial, sometimes exceeding 40% in certain populations.
For macrolide-resistant infections, second-line treatment often involves a fluoroquinolone, such as moxifloxacin. However, the emergence of resistance to this second class of antibiotics is also a growing concern. Mutations in the parC and/or gyrA genes are associated with moxifloxacin resistance, leading to cases of dual resistance where the bacteria are difficult to treat with either of the standard drug classes. Resistance testing, if available, is useful to guide therapy and avoid ineffective treatments.
Confirming Eradication and Recurrence
To confirm successful clearance, a Test of Cure (TOC) is routinely recommended for all patients who test positive for MG. This test uses the same highly sensitive nucleic acid amplification test (NAAT) that was used for the initial diagnosis. The timing of the TOC is important to avoid misleading results.
The TOC should not be conducted too soon after treatment is finished because the test can detect fragments of dead bacterial DNA. These lingering fragments cannot cause infection and can result in a false-positive reading. To ensure accuracy, the test is typically recommended at least 3 to 4 weeks after the patient completes the final dose of antibiotics.
A positive result on a TOC performed at the proper time indicates treatment failure, meaning the bacteria were never fully eliminated. A positive test occurring many months later, without a preceding TOC, requires clinical assessment to determine if it is a late failure or a new reinfection. In either case, the positive test confirms the need for further management and treatment.
Strategies for Preventing Future Infections
Preventing MG recurrence involves both medical action and changes in sexual behavior. The most effective way to prevent reinfection is to ensure all recent sexual partners are tested and treated simultaneously. Since the infection is often asymptomatic, partners can transmit the bacteria unknowingly, creating a cycle of ping-pong infection.
Avoid all sexual contact until both the patient and all partners have completed their full course of antibiotics. Ideally, sexual activity should be postponed until a negative Test of Cure result is confirmed for the patient, which usually takes about three to four weeks post-treatment. Consistent and correct use of barrier methods, such as condoms, during all sexual activity can also significantly reduce the risk of acquiring or transmitting the bacteria.
Condoms provide a physical barrier against the bacteria during vaginal, anal, and oral sex, though no method offers 100% protection. Open communication with partners about the infection and the need for testing and treatment is a fundamental step in breaking the chain of transmission. Adhering to these strategies is crucial for long-term clearance and prevention.