What are the differences in discharge between Mycoplasma (M.) genitalium, gonorrhea (Neisseria gonorrhoeae), and chlamydia (Chlamydia trachomatis) infections?

Discharge Characteristics: Mycoplasma genitalium vs. Gonorrhea vs. Chlamydia

The key clinical distinction is that gonorrhea typically produces the most profuse and purulent discharge, while both Mycoplasma genitalium and chlamydia cause mucopurulent or less profuse discharge—but M. genitalium is associated with MORE symptomatic urethritis than chlamydia despite similar microscopic findings. 1, 2

Discharge Characteristics by Pathogen

Gonorrhea (Neisseria gonorrhoeae)

• Produces purulent (thick, yellow-green, pus-like) discharge that is typically the most profuse and obvious of the three pathogens 1
• Discharge is often spontaneously visible without urethral stripping 1
• Associated with more severe symptoms including anal pain and tenesmus in rectal infections compared to M. genitalium 3
• Microscopy shows abundant polymorphonuclear leukocytes (>5 WBC per high-power field) 1

Chlamydia (Chlamydia trachomatis)

• Produces mucopurulent (mucus-like with some pus) discharge that is less profuse than gonorrhea 1
• Discharge may be clear to white or slightly yellow 1
• Only 40% of men with chlamydial urethritis report symptomatic urethritis despite microscopic evidence of inflammation 2
• Often requires urethral stripping to visualize discharge 1
• Microscopy shows ≥10 WBC per high-power field in first-void urine sediment 1

Mycoplasma genitalium

• Produces mucopurulent discharge similar in appearance to chlamydia but is associated with significantly more symptomatic disease 1, 4, 2
• 73% of men with M. genitalium report symptomatic urethritis compared to only 40% with chlamydia (RR 1.8; 95% CI 1.2-2.7) 2
• Discharge characteristics include dysuria and urethral discharge in men; vaginal discharge and dysuria in women 4
• 90% of M. genitalium-positive patients show microscopic urethritis, identical to chlamydia 2
• In rectal infections, M. genitalium causes LESS anal pain and tenesmus compared to gonorrhea or chlamydia, making it more subtle clinically 3

Critical Clinical Distinctions

You Cannot Reliably Distinguish These Pathogens by Discharge Alone

• All three pathogens can present with mucopurulent or purulent discharge, and asymptomatic infections are common across all three 1, 4
• The CDC explicitly states that symptoms alone cannot differentiate these pathogens, requiring nucleic acid amplification testing (NAAT) for definitive diagnosis 1
• Up to 50% of women with gonorrhea or chlamydia do NOT have mucopurulent cervicitis despite active infection 5

Bacterial Load Does Not Correlate Between Coinfections

• M. genitalium and chlamydia bacterial loads are unrelated in coinfected patients, suggesting independent pathogenic mechanisms 6
• Coinfections occur in approximately 4-22% of cases but do not alter discharge characteristics predictably 2, 3

Practical Clinical Algorithm

When Evaluating Urethral/Vaginal Discharge:

1. Perform Gram stain microscopy if available to identify gram-negative intracellular diplococci (gonorrhea) versus non-specific inflammation 1

2. Obtain NAAT testing for all three pathogens (N. gonorrhoeae, C. trachomatis, and M. genitalium) in symptomatic patients, as discharge characteristics overlap significantly 1, 4

3. Treat empirically for both gonorrhea AND chlamydia if:

   • Local prevalence >15% 5
   • Patient unlikely to return for follow-up 5
   • Patient is sexually active and under 25 years old 5
   • Seen in STD clinic or high-prevalence setting 5

4. Consider M. genitalium testing in:

   • Persistent urethritis after treatment for gonorrhea/chlamydia 4
   • Non-gonococcal, non-chlamydial urethritis with symptoms 4, 2
   • Rectal proctitis symptoms 3

Common Pitfalls to Avoid

• Do not assume profuse discharge equals gonorrhea alone—coinfections are common and require testing for all pathogens 1, 2
• Do not rely on symptom severity to rule out infection—asymptomatic infections occur in all three pathogens 1, 4, 2
• Do not forget M. genitalium in persistent/recurrent urethritis—it accounts for 10-35% of non-chlamydial, non-gonococcal urethritis 4
• Do not continue empiric antibiotics indefinitely for culture-negative persistent discharge—consider non-infectious causes like cervical ectopy inflammation 7