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)

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