Which of the following organisms is NOT typically associated with pelvic inflammatory disease?

Explanation

## Microbiology of PID **Key Point:** Pelvic inflammatory disease is primarily caused by sexually transmitted pathogens that ascend from the lower genital tract. The classic causative organisms are *Neisseria gonorrhoeae* and *Chlamydia trachomatis*, which account for the majority of cases. ### Common PID Pathogens | Organism | Frequency | Route | Notes | |----------|-----------|-------|-------| | *Neisseria gonorrhoeae* | Very common | STI | Gram-negative diplococcus | | *Chlamydia trachomatis* | Very common | STI | Intracellular; often asymptomatic | | *Mycoplasma genitalium* | Emerging pathogen | STI | Associated with persistent/recurrent PID | | *Anaerobes* (Bacteroides, Prevotella) | Common (polymicrobial) | Endogenous flora | Secondary invaders | | *Streptococcus agalactiae* (GBS) | Rare in PID | Endogenous | Associated with postpartum/post-procedural infection, NOT typical PID | | *Streptococcus pneumoniae* | **NOT typical** | Respiratory | Causes pneumonia, meningitis, NOT ascending genital infection | **High-Yield:** *Streptococcus pneumoniae* is a respiratory pathogen and does not cause PID. It is not part of the normal vaginal flora and does not ascend from the lower genital tract. **Clinical Pearl:** Modern PID is often polymicrobial, involving both STI pathogens (gonorrhea, chlamydia) and anaerobic bacteria from the endogenous vaginal flora. ### Pathophysiology of Ascending Infection 1. Sexually transmitted pathogen colonizes endocervix 2. Organism ascends through cervical mucus (especially during menses) 3. Reaches endometrium → fallopian tubes → peritoneal cavity 4. Secondary anaerobic bacteria join the infection 5. Results in polymicrobial upper genital tract infection