A 28-year-old woman presents with lower abdominal pain, vaginal discharge, and fever for 5 days. On examination, she has cervical motion tenderness and adnexal tenderness. She is sexually active with multiple partners and does not use barrier contraception. What is the most common causative organism in pelvic inflammatory disease?

Explanation

## Most Common Causative Organism in PID **Key Point:** Chlamydia trachomatis is the most common causative organism of pelvic inflammatory disease globally, accounting for approximately 40–50% of cases. Neisseria gonorrhoeae accounts for 20–30% of cases, and many cases are polymicrobial. ### Epidemiology and Frequency | Organism | Frequency | Clinical Notes | |----------|-----------|----------------| | Chlamydia trachomatis | 40–50% | Most common; often asymptomatic cervicitis; serovars D–L | | Neisseria gonorrhoeae | 20–30% | More acute presentation; gram-negative diplococcus | | Polymicrobial (anaerobes, gram-negatives) | 20–30% | Mixed aerobic and anaerobic flora | | Mycoplasma genitalium | 5–10% | Emerging pathogen; associated with treatment failures | | Treponema pallidum | Rare | Causes syphilis, not typical PID | **High-Yield:** Chlamydia trachomatis is the **single most common organism** in PID because: 1. High prevalence in sexually active populations 2. Often asymptomatic, leading to delayed diagnosis and upper genital tract ascension 3. Serovars D–L are associated with genital infection 4. Causes chronic inflammation and tubal damage **Clinical Pearl:** Although Neisseria gonorrhoeae causes more acute and symptomatic PID, Chlamydia is more frequent overall because many chlamydial infections remain undiagnosed at the cervical level and ascend silently to the upper tract. **Warning:** Do not confuse frequency with severity. Gonorrhea may present more acutely and dramatically, but Chlamydia is statistically more common and more likely to cause silent tubal damage. ### Pathophysiology Chlamydia trachomatis is an obligate intracellular pathogen that: - Infects the columnar epithelium of the endocervix - Triggers a chronic inflammatory response - Ascends to the fallopian tubes, causing salpingitis - Leads to tubal scarring, stricture, and ectopic pregnancy risk [cite:Jeffcoate's Principles of Gynaecology Ch 24]