Vhlamydia infection
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"Chlamydia trachomatis"[MeSH Terms] AND treatment
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Chlamydia trachomatis infection CDC treatment guidelines 2025
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Chlamydia Infection
Overview
Chlamydia trachomatis is the most common bacterial sexually transmitted infection in the United States and a leading cause of preventable blindness worldwide. It is an obligate intracellular parasite that was once mistaken for a virus because it can pass through 0.45-μm filters - but it possesses all the properties of gram-negative bacteria: dual membranes, both DNA and RNA, prokaryotic ribosomes, and susceptibility to antibiotics.
- Medical Microbiology, 9th ed.
The Organism
Unique Biology
Chlamydiae exist in two distinct morphological forms:
| Form | Size | State | Function |
|---|---|---|---|
| Elementary Body (EB) | 300-400 nm | Metabolically inactive | Infectious - binds host cell receptors, survives extracellularly |
| Reticulate Body (RB) | 800-1000 nm | Metabolically active | Non-infectious - replicates intracellularly |
Life cycle:
- EB attaches to microvilli of columnar/cuboidal/transitional epithelial cells
- EB is actively taken up into a phagosome
- If outer membrane is intact, phagolysosomal fusion is inhibited - the bacterium survives
- Within 6-8 hours, EBs reorganize into RBs
- RBs replicate by binary fission over ~48 hours
- RBs convert back to EBs, which are released to infect new cells
Chlamydiae are energy parasites - they rely on host ATP. The major outer membrane protein (MOMP) is species-specific and responsible for the 18 serologic variants (serovars) of C. trachomatis.
- Medical Microbiology, 9th ed.
Species and Serotypes
| Species | Biovars / Serovars | Diseases |
|---|---|---|
| C. trachomatis | Serovars A, B, Ba, C | Ocular trachoma (leading cause of preventable blindness) |
| C. trachomatis | Serovars D-K | Urogenital infections, neonatal conjunctivitis, infant pneumonia |
| C. trachomatis | Serovars L1, L2, L3 | Lymphogranuloma venereum (LGV) |
| C. pneumoniae | TWAR strain | Bronchitis, pneumonia, sinusitis, pharyngitis |
| C. psittaci | Many biovars | Psittacosis (atypical pneumonia from birds) |
- Medical Microbiology, 9th ed.
Key distinguishing lab feature: C. trachomatis produces iodine-staining glycogen in inclusions; C. pneumoniae and C. psittaci do not. C. trachomatis is also susceptible to sulfonamides; the others are not.
Clinical Presentations
1. Urogenital Infections (Serovars D-K)
In women (often asymptomatic - ~70-80%):
- Mucopurulent cervicitis
- Urethritis, urethral syndrome
- Bartholin gland infection
- Endometritis, salpingitis
In men (often asymptomatic):
- Urethritis (mucopurulent discharge, dysuria)
- Epididymitis
- Proctitis (in MSM)
Complications:
-
Pelvic Inflammatory Disease (PID): 40% of women with untreated chlamydia will develop PID
-
Ectopic pregnancy
-
Chronic pelvic pain
-
Tubal factor infertility
-
Increased risk of HIV acquisition and transmission
-
Reactive arthritis (Reiter syndrome: urethritis + conjunctivitis + arthritis)
-
Smith and Tanagho's General Urology, 19th ed.; Kaplan & Sadock's Comprehensive Textbook of Psychiatry
2. Ocular Trachoma (Serovars A, B, Ba, C)
- Repeated infections cause chronic follicular conjunctivitis
- Scarring of conjunctiva → entropion → corneal abrasion → blindness
- Trachoma serovar A does not induce lasting immunity - critical to why reinfection perpetuates disease
- Endemic in sub-Saharan Africa, Middle East, South Asia, South America
3. Lymphogranuloma Venereum - LGV (Serovars L1, L2, L3)
Three stages:
- Primary lesion: Small, painless papule/ulcer at inoculation site (often unnoticed); heals spontaneously
- Inguinal stage: Painful inguinal lymphadenopathy (buboes), fever, malaise; nodes may suppurate and rupture; the "groove sign" (enlargement above and below inguinal ligament)
- Late stage: Destructive fibrosis, elephantiasis of genitalia, rectal strictures, fistulae
- Andrews' Diseases of the Skin; Yamada's Textbook of Gastroenterology
Recent concern: Outbreaks of LGV proctitis in men who have sex with men (MSM), presenting as severe hemorrhagic proctocolitis mimicking inflammatory bowel disease.
4. Neonatal Infections
Transmission occurs in ~50% of infants born vaginally to infected mothers (and in some cesarean deliveries with intact membranes).
| Manifestation | Onset | Features |
|---|---|---|
| Neonatal conjunctivitis | 5-14 days of life | Ocular congestion, edema, discharge |
| Infant pneumonia | 4-12 weeks after birth | Afebrile, staccato cough, tachypnea, rales; hyperinflation on CXR |
Note: Topical erythromycin prophylaxis given at birth prevents gonococcal ophthalmia but does NOT prevent chlamydial conjunctivitis.
- Creasy & Resnik's Maternal-Fetal Medicine, Principles and Practice
Diagnosis
| Test | Notes |
|---|---|
| NAATs (PCR, strand displacement) | Gold standard - most sensitive and specific; FDA-cleared for urine, vaginal, cervical, urethral swabs |
| Culture | Highly specific, but relatively insensitive; requires cell culture; used for medico-legal cases |
| Direct fluorescent antibody (DFA) | Relatively insensitive |
| ELISA (antigen detection) | Relatively insensitive |
| Serology | Useful mainly for LGV (high IgG titers) and C. pneumoniae; not reliable for genital chlamydia |
The 2026 systematic review on point-of-care tests for C. trachomatis (Manabe et al., Clin Infect Dis, 2026) found that while POC NAATs are now available, lab-based NAATs remain the most sensitive.
Screening recommendations (CDC 2021 guidelines, still current):
- Annual screening of all sexually active women aged <25 years
- Older women at increased risk (new sex partner, multiple partners, partner with STI)
- Men who have sex with men (urethral + rectal + pharyngeal)
Treatment
First-Line (CDC 2021 / Current Recommendations)
| Infection Type | First-Line | Alternatives |
|---|---|---|
| Uncomplicated urogenital/rectal | Doxycycline 100 mg PO twice daily × 7 days | Azithromycin 1 g PO × 1 (less effective for rectal infections); levofloxacin 500 mg × 7d |
| Pregnancy | Azithromycin 1 g PO × 1 | Amoxicillin 500 mg PO 3× daily × 7d |
| LGV | Doxycycline 100 mg PO twice daily × 21 days | Erythromycin |
| Neonatal conjunctivitis / infant pneumonia | Oral erythromycin base 50 mg/kg/day ÷ 4 doses × 14d | Azithromycin 20 mg/kg/day × 3 days |
| C. pneumoniae | Doxycycline or erythromycin | Clarithromycin, azithromycin, levofloxacin, moxifloxacin |
| C. psittaci (psittacosis) | Doxycycline | Azithromycin |
Important: Azithromycin 1 g single dose was previously first-line but was downgraded because doxycycline 7-day regimen shows superior efficacy, especially for rectal infections. Current CDC STI guidelines recommend doxycycline as preferred.
- Washington Manual of Medical Therapeutics; Katzung's Basic and Clinical Pharmacology, 16th ed.
Neonatal treatment efficacy is ~80% - follow-up is recommended and a second course may be needed.
Prevention and Control
- Condom use and reducing number of sexual partners
- Prompt treatment of sexual partners (partner notification and treatment are essential; reinfection is common due to lack of partner treatment)
- Prenatal screening - detecting and treating maternal infection before delivery is the most effective way to prevent neonatal conjunctivitis and pneumonia
- Population screening programs (cost-effective per [2023 systematic review, PMID 37881345])
- No vaccine available; trachoma serovar A's failure to induce immunity is a major barrier
Key Differentiating Points vs. Gonorrhea
| Feature | Chlamydia | Gonorrhea |
|---|---|---|
| Incubation | 7-21 days | 2-7 days |
| Discharge | Mucoid/watery | Thick purulent |
| Intracellular organism | Obligate intracellular | Facultative intracellular (gram-neg diplococci) |
| First-line treatment | Doxycycline 7 days | Ceftriaxone IM single dose |
| Asymptomatic rate | Very high (70-80% women) | Lower but still significant |
Summary Table: C. trachomatis Serovars
| Serovars | Disease |
|---|---|
| A, B, Ba, C | Trachoma (ocular) |
| D, E, F, G, H, I, J, K | Urethritis, cervicitis, PID, epididymitis, neonatal infections |
| L1, L2, L3 | Lymphogranuloma venereum (LGV) |
Sources: Medical Microbiology 9e | Creasy & Resnik's Maternal-Fetal Medicine | Washington Manual of Medical Therapeutics | Katzung's Basic and Clinical Pharmacology 16e | Smith and Tanagho's General Urology 19e | Andrews' Diseases of the Skin | CDC STI Treatment Guidelines 2021 | 2025 European IUSTI Guideline on C. trachomatis
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