Chlamydial Infections¶
Chapter 194 | Part 5: Infectious Diseases
KEY CLINICAL POINTS¶
- Chlamydial infections are the most prevalent bacterial sexually transmitted infections (STIs) globally, with 1.65 million cases reported in the U.S. in 2022.
- C. trachomatis causes genital infections, pelvic inflammatory disease (PID), and neonatal conjunctivitis, while C. pneumoniae is linked to respiratory diseases and atherosclerosis.
- Diagnosis relies on nucleic acid amplification tests (NAATs) for urine/vaginal swabs, with serologic tests (MIF) for LGV and psittacosis.
- Doxycycline is the first-line treatment for uncomplicated genital infections, while azithromycin is preferred for pregnant women and LGV.
- Reactive arthritis and perihepatitis (Fitz-Hugh-Curtis syndrome) are complications of chlamydial infections, often requiring multidisciplinary management.
1. DEFINITION & OVERVIEW¶
Chlamydial infections are caused by obligate intracellular bacteria (Chlamydia spp.) that infect the urogenital tract, respiratory system, and eyes. C. trachomatis is the most common pathogen, while C. pneumoniae and C. psittaci cause respiratory and systemic infections. Ureaplasma and Mycoplasma genitalium are also significant pathogens in urogenital infections.
Table 194-1: Diagnostic Tests for Sexually Transmitted and Perinatal Chlamydia trachomatis Infection¶
| INFECTION | SUGGESTIVE SIGNS/SYMPTOMS | PRESUMPTIVE DIAGNOSISa | CONFIRMATORY TEST OF CHOICE |
|---|---|---|---|
| Men | NGU, PGU | Discharge, dysuria | Urine NAAT for C. trachomatis |
| Men | Epididymitis | Unilateral intrascrotal swelling, pain, tenderness; fever; NGU | Urine NAAT for C. trachomatis |
| Women | Cervicitis | Mucopurulent cervical discharge, sustained endocervical bleeding | Vaginal (or cervical) NAAT for C. trachomatis |
| Women | Salpingitis | Lower abdominal pain, cervical motion tenderness, adnexal tenderness or masses | Vaginal (or cervical) NAAT for C. trachomatis |
| Adults of Either Sex | Proctitis | Rectal pain, discharge, tenesmus, bleeding; history of receptive anorectal intercourse | Rectal NAAT for C. trachomatis |
| INFECTION | SUGGESTIVE SIGNS/SYMPTOMS | PRESUMPTIVE DIAGNOSISa | CONFIRMATORY TEST OF CHOICE |
|---|---|---|---|
| Neonates | Conjunctivitis | Purulent conjunctival discharge 5–12 days after birth | Tissue culture, conjunctival NAAT for C. trachomatis |
1.1 Etiologic Agents¶
C. trachomatis (genital, ocular, and respiratory infections), C. pneumoniae (respiratory infections), C. psittaci (psittacosis), Ureaplasma species, and Mycoplasma genitalium (urogenital infections).
1.2 Pathogenesis¶
Chlamydiae replicate within host cells, forming intracellular inclusions. They evade immune responses through antigenic variation and persistence. C. pneumoniae may contribute to atherosclerosis and chronic lung diseases.
2. EPIDEMIOLOGY¶
Global prevalence: 50 million prevalent cases in men and 77 million in women in 2020. U.S. incidence: 1.65 million cases in 2022. Risk factors include young age (<25), multiple sexual partners, and lack of barrier contraception. C. trachomatis is most common in women aged 20–24, while C. pneumoniae is widespread in industrialized and developing countries.
2.1 Demographics¶
Highest incidence in women aged 20–24 and men aged 20–23. Neonatal infections: 20–30% of infants exposed to C. trachomatis develop conjunctivitis, with 10–15% developing pneumonia.
2.2 Geographic Distribution¶
C. trachomatis is endemic in Africa, Asia, Latin America, and the Caribbean. C. psittaci outbreaks occur in poultry workers and pet bird owners.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Chlamydiae replicate within host cells, forming intracellular inclusions. C. trachomatis causes genital infections, while C. pneumoniae is linked to respiratory diseases and atherosclerosis. Ureaplasma and Mycoplasma genitalium contribute to urogenital infections and PID. C. psittaci causes psittacosis in humans via avian exposure.
3.1 Molecular Mechanisms¶
Chlamydiae use a type III secretion system to manipulate host cell processes. C. pneumoniae outer-membrane proteins may induce vascular inflammation and atherosclerosis.
3.2 Immune Evasion¶
Antigenic variation via major outer-membrane protein (MOMP) polymorphisms allows persistence. Host immune responses (e.g., IFN- γ ) may exacerbate tissue damage.
4. CLINICAL FEATURES¶
Genital infections: urethritis, cervicitis, PID. Respiratory: pneumonia, bronchitis. Ocular: trachoma, conjunctivitis. Complications include infertility, ectopic pregnancy, and reactive arthritis. Neonatal infections: conjunctivitis, pneumonia.
4.1 Genital Infections¶
C. trachomatis causes urethritis (30–50% of NGU cases), cervicitis, and PID. Ureaplasma and M. genitalium contribute to chronic pelvic pain and infertility.
4.2 Respiratory Infections¶
C. pneumoniae causes atypical pneumonia (1–2% of community-acquired pneumonia cases). Chronic infection may exacerbate asthma and COPD.
5. DIFFERENTIAL DIAGNOSIS¶
For genital infections: gonorrhea, HSV, trichomoniasis. For respiratory infections: Mycoplasma pneumoniae, viral pneumonia. For ocular infections: HSV, bacterial conjunctivitis. For neonatal infections: gonococcal ophthalmia, HSV, bacterial pneumonia.
5.1 Urethritis¶
Differentiate from gonococcal urethritis (purulent discharge) and HSV (painful ulcers).
5.2 PID¶
Distinguish from tubo-ovarian abscess, endometriosis, and pelvic tumors.
6. INVESTIGATIONS & DIAGNOSIS¶
NAATs for urine/vaginal swabs are the gold standard. Serologic tests (MIF, CF) for LGV and psittacosis. PCR for respiratory samples. C. pneumoniae diagnosis via PCR or serology. Neonatal testing: conjunctival swabs and nasopharyngeal specimens.
6.1 Diagnostic Tests¶
NAATs (urine, vaginal swabs), PCR (respiratory samples), serologic tests (MIF, CF), and culture (specialized labs).
6.2 Imaging¶
Ultrasound for PID, CT/MRI for complicated infections. Laparoscopy for diagnosing salpingitis.
7. MANAGEMENT & TREATMENT¶
Doxycycline (100 mg BID x7 days) for uncomplicated genital infections. Azithromycin (1g single dose) for pregnant women and LGV. C. pneumoniae: macrolides or fluoroquinolones. Psittacosis: doxycycline. PID: doxycycline + metronidazole. Post-exposure prophylaxis for sexual partners.
7.1 Genital Infections¶
Doxycycline (100 mg BID x7 days) or azithromycin (1g single dose). Avoid tetracyclines in pregnancy.
7.2 PID¶
Doxycycline 100 mg BID x14 days + metronidazole 500 mg BID x14 days. Surgical intervention for abscesses.
8. PROGNOSIS & COMPLICATIONS¶
Untreated infections lead to PID, infertility, ectopic pregnancy, and chronic pelvic pain. Neonatal complications: blindness, pneumonia. Reactive arthritis (4–15% of NGU cases) and perihepatitis (Fitz-Hugh-Curtis syndrome). C. pneumoniae may contribute to atherosclerosis and cardiovascular disease.
8.1 Long-term Outcomes¶
PID increases risk of tubal infertility (up to 50% of cases). Chronic infections may cause scarring and fibrosis.
8.2 Neonatal Complications¶
Ophthalmia neonatorum (50% of exposed infants) and pneumonia (10–15% of cases).
9. SPECIAL CONSIDERATIONS¶
Pregnancy: screen all pregnant women <25 and those at risk. Neonatal prophylaxis: erythromycin ophthalmic ointment. HIV-positive patients have higher risk of LGV and treatment failure. In elderly patients, C. pneumoniae may cause severe pneumonia requiring ICU admission.
9.1 Pregnancy¶
Screen all pregnant women <25 and those at risk. Treat with doxycycline or azithromycin. Neonatal prophylaxis: erythromycin ointment.
9.2 HIV Co-infection¶
HIV-positive patients have higher risk of LGV and treatment failure. Monitor for drug resistance.
10. KEY POINTS & CLINICAL PEARLS¶
- Chlamydial infections are the most common bacterial STI, with 1.65 million cases in the U.S. in 2022. 2. NAATs are the gold standard for diagnosis. 3. Doxycycline is first-line for uncomplicated genital infections. 4. PID is a major complication of untreated infections. 5. Neonatal conjunctivitis and pneumonia require prompt treatment. 6. Reactive arthritis occurs in 1–2% of NGU cases. 7. C. pneumoniae may contribute to atherosclerosis and cardiovascular disease.