What causes Pelvic Inflammatory Disease (PID) in women?

Causes of Pelvic Inflammatory Disease in Women

Pelvic inflammatory disease (PID) is primarily caused by sexually transmitted pathogens, particularly Neisseria gonorrhoeae and Chlamydia trachomatis, along with a variety of anaerobic and aerobic bacteria that ascend from the lower genital tract to the upper genital tract. 1

Primary Causative Pathogens

Sexually Transmitted Organisms

• Neisseria gonorrhoeae: Found in 27-80% of cervical samples from women with PID 1
• Chlamydia trachomatis: Isolated from the cervix in 5-39% of women with PID 1
• Mycoplasma genitalium: Emerging as an important pathogen in PID 2

Other Bacteria Commonly Involved (25-50% of cases)

• Anaerobic bacteria:

  • Bacteroides species
  • Peptostreptococcus species
  • Peptococcus species

• Aerobic/facultative bacteria:

  • Gardnerella vaginalis
  • Streptococcus species
  • Escherichia coli
  • Haemophilus influenzae 1

Pathogenesis of PID

PID develops through several key mechanisms:

1. Direct canalicular spread: The primary route of infection is ascending spread from the endocervix to the endometrium and fallopian tubes 1

2. Noncanalicular spread: Can occur via parametrial lymphatics 1

3. Contributing factors that facilitate infection:

   • Uterine instrumentation (e.g., IUD insertion)
   • Hormonal changes during menstruation
   • Retrograde menstruation
   • Organism-specific virulence factors 1
   • Bacterial vaginosis (BV) - serves as an antecedent to polymicrobial PID 3

Clinical Implications and Risk Factors

• Many women with PID have minimal or no symptoms ("silent PID"), which can still lead to serious reproductive consequences 3

• After a single episode of PID:

  • Approximately 12% of women become infertile
  • Risk of ectopic pregnancy increases sevenfold
  • Risk of infertility increases dramatically with multiple episodes (25% after two episodes, over 50% after three or more) 3

• Risk factors that increase likelihood of developing PID:

  • Multiple sexual partners
  • History of sexually transmitted infections
  • Young age (highest rates in women aged 15-24)
  • Non-use of barrier contraceptives 1

Important Clinical Considerations

• The polymicrobial nature of PID means that treatment must provide broad-spectrum coverage 4

• PID caused by Chlamydia tends to be more subtle or asymptomatic compared to gonococcal PID, making it more likely to go undetected and untreated 4

• Both N. gonorrhoeae and C. trachomatis employ immune evasion mechanisms that allow them to survive within host epithelial cells and neutrophils 5

• Early diagnosis and treatment are crucial to prevent long-term sequelae such as infertility, chronic pelvic pain, and ectopic pregnancy 6

• Prevention strategies include:

  • Regular screening for chlamydial and gonococcal infections
  • Prompt treatment of cervicitis and bacterial vaginosis
  • Consistent condom use
  • Reduction in number of sexual partners 1

The polymicrobial nature of PID and the ability of causative organisms to evade host immune responses make this condition particularly challenging to diagnose and treat, highlighting the importance of prevention strategies and early intervention.