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Pelvic Inflammatory Disease (PID) - Integrated Microbiology & Gynaecology

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1. Definition

"PID is a clinical diagnosis implying upper genital tract infection and inflammation present at any point along a continuum that includes endometritis, salpingitis, and peritonitis." - Berek & Novak's Gynecology

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2. Microbiology and Etiology

Primary STI Pathogens (Cervicitis Agents Ascending Upward)

Endogenous/BV-Associated Organisms

• Prevotella spp.
• Peptostreptococcus spp.
• Gardnerella vaginalis
• Mobiluncus spp.

Aerobic & Facultative Organisms

• Escherichia coli
• Haemophilus influenzae
• Group B streptococci
• Group A streptococci (less common)
• Streptococcus pneumoniae (rare)

Special Causes

• Hematogenous spread: Mycobacterium tuberculosis (causes TB salpingitis - "pipe-stem" tubes), Staphylococcus aureus
• Secondary spread: from appendicitis, diverticulitis, regional ileitis
• Post-procedural: IUD insertion, D&C, hysterosalpingography, termination of pregnancy

N. gonorrhoeae causes 10-40% of women with untreated lower-tract infection to progress to PID. - Goldman-Cecil Medicine

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3. Pathogenesis

1. Colonization of endocervix by N. gonorrhoeae or C. trachomatis (or both)
2. Disruption of cervical mucus barrier - BV enzymes, menstruation (menstrual blood is a growth medium; onset of symptoms at menstruation is typical)
3. Ascending spread to endometrium → endometritis → salpingitis → peritonitis
4. Polymicrobial superinfection - anaerobes join as disease progresses
5. Immune-mediated damage - especially with C. trachomatis; repeated exposure causes the greatest inflammatory damage (immunopathology via delayed hypersensitivity)
6. TOA formation - agglutination of pelvic organs (tube + ovary + bowel) with pus collection

• Menstruation (most episodes begin peri-menstrually)
• IUD threads may act as a wick
• Instrumentation (IUD insertion, D&C)
• BV disrupting the protective lactobacilli

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4. Epidemiology & Risk Factors

• USA: ~800,000 women develop PID annually; hospitalizations 70,000-100,000/year
• Age: Peak incidence in sexually active women aged 15-25 years
• Risk factors:
  • Active endocervical gonorrheal or chlamydial infection
  • Bacterial vaginosis
  • History of prior PID (each episode increases risk of the next)
  • Multiple sexual partners / new sexual partner
  • Vaginal douching (disrupts flora)
  • Recent IUD insertion (risk elevated in first 3 weeks post-insertion)
  • Adolescence
  • HIV infection
• Protective factors: Oral contraceptive pills (thicken cervical mucus, reduce menstrual flow); condom use; prior tubal ligation

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5. Clinical Features

Symptoms

• Pelvic/lower abdominal pain - most common; bilateral, constant or intermittent, typically worse with movement, menses, and coitus
• Vaginal discharge (purulent/mucopurulent)
• Abnormal uterine bleeding (menorrhagia, metrorrhagia)
• Fever (>38.3°C), chills
• Nausea and vomiting (suggests severe disease or TOA)
• Urinary symptoms

Note: Chlamydial PID is classically "silent" or subclinical - it is an important cause of unrecognized tubal damage. - Sherris & Ryan's Medical Microbiology

Signs

• Cervical motion tenderness (CMT) - the hallmark sign (suggests peritoneal irritation)
• Uterine/adnexal tenderness on bimanual examination
• Elevated temperature and tachycardia
• Abdominal distension with decreased bowel sounds (secondary ileus in severe disease)
• Direct/rebound abdominal tenderness
• Cervical or vaginal mucopurulent discharge
• Right upper quadrant pain - Fitz-Hugh-Curtis syndrome (perihepatitis)
  • Violin-string adhesions between the liver capsule and peritoneum
  • Can mimic cholecystitis or hepatitis
  • Occurs in both gonococcal and chlamydial PID

Severity Staging

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6. Diagnosis

CDC Minimum Criteria (Initiate Treatment if Present)

1. Cervical motion tenderness
2. Uterine tenderness
3. Adnexal tenderness

Additional Criteria (Increase Specificity)

Most Specific (Definitive) Criteria

• Endometrial biopsy showing endometritis (plasma cell infiltration)
• Laparoscopy - gold standard: tubal edema, erythema, purulent exudate from tubes
  • Note: Clinical diagnosis confirmed laparoscopically in only ~70% of cases
• Transvaginal ultrasound/MRI: thickened fluid-filled fallopian tubes, TOA, free pelvic fluid

Imaging

• Transvaginal ultrasound: first-line; shows tubal hyperemia, thickened/fluid-filled tubes, TOA; can guide drainage
• MRI: better delineates equivocal ultrasound findings
• CT abdomen/pelvis: evaluates for complications beyond the pelvis (perihepatitis, generalized peritonitis)

Differential Diagnosis

• Ectopic pregnancy (always rule out with βhCG)
• Appendicitis
• Ovarian cyst torsion or rupture
• Urinary tract infection / pyelonephritis
• Endometriosis
• Inflammatory bowel disease
• Diverticulitis

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7. Tubo-Ovarian Abscess (TOA)

• End-stage PID: agglutination of tube, ovary, and bowel forming a palpable complex
• Bimanual examination reveals a tender adnexal mass
• ESR >19.5 mm/hr and CRP >11.5 mg/L predict TOA (vs. PID without TOA)
• Management:
  • ~75% respond to parenteral antibiotics alone (inpatient)
  • Failure after 72 hours → percutaneous image-guided drainage (up to 90% success)
  • Surgical drainage (posterior colpotomy, or laparoscopy/laparotomy) for refractory cases or rupture
  • Ruptured TOA = surgical emergency

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8. Treatment

General Principles

• All regimens must cover N. gonorrhoeae, C. trachomatis, and anaerobes
• M. genitalium should be addressed if present/suspected
• Remove IUD if no clinical improvement within 72 hours
• Treat all sexual partners empirically for gonorrhea and chlamydia

Indications for Hospitalization

1. Diagnosis uncertain; surgical emergency (appendicitis, ectopic) cannot be excluded
2. Pregnancy
3. Suspected or confirmed TOA
4. Severe illness: high fever, nausea/vomiting precluding oral therapy
5. Failure to respond to outpatient therapy within 72 hours
6. HIV infection
7. Non-compliance with outpatient regimen likely
8. Some experts recommend hospitalization for all adolescents

Antibiotic Regimens

Outpatient (Mild-Moderate Disease)

Inpatient Regimen A (Preferred)

Inpatient Regimen B (Especially for TOA)

A 2025 meta-analysis found that fluoroquinolone-based regimens for PID showed effectiveness but rising resistance to fluoroquinolones is a concern [PMID: 41327742].

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9. Complications and Long-Term Sequelae

"Even with successful treatment, PID can cause tubal scarring and tubal obstruction. After one episode of PID, almost 10% of women may develop tubal occlusion." - Goldman-Cecil Medicine

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10. PID in Special Circumstances

PID and IUDs

• IUDs are associated with increased risk, especially in first 3 weeks post-insertion
• Remove IUD if no improvement; however, IUD removal is NOT mandatory if response is good
• If pregnancy occurs with IUD in situ and PID is present - IUD should be removed

PID and Pregnancy

• PID as coexistent with intrauterine pregnancy is rare
• If pregnancy test is positive in suspected PID → consider ectopic pregnancy, infected abortion, or infected IUP
• Pregnant women with salpingitis: mandatory hospitalization

Subclinical PID

• Particularly with C. trachomatis - may present with only subtle symptoms
• Is a major cause of "unexplained" tubal factor infertility
• Screening sexually active women ≤25 years annually for chlamydia reduces PID incidence by 56% (CDC/USPSTF recommendation)

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11. Prevention

• Annual NAAT screening for C. trachomatis in all sexually active women ≤25 years
• Consistent condom use
• Reducing number of sexual partners
• Treating BV (which facilitates ascending infection)
• Prompt treatment of lower genital tract STIs before ascent occurs
• Avoiding vaginal douching

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12. Summary Table - Organism-Specific Features

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