Pelvic Inflammatory Disease (PID): Bacterial Causes & Risk Factors

Pelvic Inflammatory Disease (PID) is an infection of the upper female reproductive tract (uterus, fallopian tubes, ovaries). It typically results from ascending infection from the cervix. Key pathogens include:

Primary Sexually Transmitted Pathogens

• Chlamydia trachomatis – Most common cause (≈30–40% of PID cases). Often asymptomatic initially.
• Neisseria gonorrhoeae – Second most common (≈10–20%). Can cause more acute, severe symptoms.
• Mycoplasma genitalium – Emerging recognized pathogen; associated with cervicitis and PID.

Polymicrobial / Endogenous Flora

In many cases, PID involves a mix of organisms ascending from the vaginal microbiome:

• Anaerobes: Bacteroides, Prevotella, Peptostreptococcus spp.
• Facultative anaerobes: Gardnerella vaginalis, Haemophilus influenzae, Enteric Gram-negatives (E. coli, Klebsiella).
• Other: Streptococcus agalactiae (Group B Strep), Ureaplasma urealyticum.

Risk Factors for Ascending Infection

• Multiple sexual partners / new partner
• Inconsistent condom use
• Prior PID or STI
• Age <25 (cervical ectopy increases susceptibility)
• Douching (disrupts vaginal flora, facilitates ascent)
• IUD insertion (transiently increased risk in first 3 weeks)
• Gynecologic procedures (hysteroscopy, abortion, D&C)

Clinical Implication

Empiric PID treatment must cover both STI pathogens (chlamydia, gonorrhea) and anaerobes/Gram-negatives. CDC regimens typically combine a cephalosporin (ceftriaxone) + doxycycline ± metronidazole.