Chlamydia trachomatis Infections

1. Clinical Overview

Definition and Importance

Chlamydia trachomatis is an obligate intracellular Gram-negative bacterium that causes the most prevalent bacterial sexually transmitted infection worldwide. [1] The organism's unique developmental cycle, transitioning between infectious elementary bodies and replicative reticulate bodies, enables persistent intracellular infection while evading host immune responses. The infection is characterised by its largely asymptomatic nature, with 70-80% of women and approximately 50% of men remaining unaware of their infection, facilitating ongoing transmission and delayed sequelae. [2]

The clinical significance of chlamydial infection extends far beyond the acute episode. Untreated or recurrent infections in women lead to ascending genital tract infection, resulting in pelvic inflammatory disease (PID), tubal scarring, ectopic pregnancy, and tubal factor infertility. The economic burden is substantial: while treatment of uncomplicated infection costs approximately $20-30, the downstream costs of assisted reproduction technologies for chlamydia-induced infertility exceed $15,000 per IVF cycle. [3] This cost-benefit analysis underpins the rationale for population-level screening programmes.

Serovar Classification

C. trachomatis comprises 18 serovars with distinct tissue tropism and disease manifestations:

Serovar Group	Serovars	Clinical Syndrome	Geographic Distribution
Urogenital	D, Da, E, F, G, H, I, Ia, J, K	Urethritis, cervicitis, PID, epididymitis, proctitis, neonatal infections	Worldwide
LGV	L1, L2, L2a, L2b, L3	Lymphogranuloma venereum - invasive lymphatic disease	Endemic in Africa, Southeast Asia, Caribbean; emerging in MSM globally
Trachoma	A, B, Ba, C	Ocular trachoma - leading cause of infectious blindness	Endemic in sub-Saharan Africa, Middle East, South Asia

The urogenital serovars (D-K) are non-invasive and cause superficial mucosal infection. In contrast, the LGV serovars (L1-L3) possess enhanced invasive capacity, penetrating through epithelial barriers to infect regional lymph nodes and causing more severe systemic disease. [4]

Key Clinical Facts

Parameter	Value	Clinical Significance
Global Prevalence	129 million new cases annually (WHO 2020)	Most common bacterial STI worldwide
UK Prevalence	3-4% in sexually active under-25s	Target population for screening
Asymptomatic Rate (Women)	70-80%	Justifies opportunistic screening
Asymptomatic Rate (Men)	50%	Partner notification essential
Incubation Period	7-21 days (typically 1-3 weeks)	Window period for testing
Test Positivity Window	14 days post-exposure	Earlier testing may miss infection
Co-infection with Gonorrhoea	20-40%	Dual testing mandatory

Clinical Pearl: The Rule of Thirds for Untreated PID: Approximately one-third of women with untreated PID will experience recurrent infection, one-third will develop chronic pelvic pain from adhesions, and one-third will suffer tubal factor infertility. This underscores the importance of early detection and treatment.

2. Microbiology and Pathophysiology

Unique Developmental Cycle

C. trachomatis exhibits a biphasic developmental cycle lasting 48-72 hours, alternating between two morphologically and functionally distinct forms: [5]

Elementary Body (EB)

Diameter: 200-300 nm
Infectious, extracellular form
Metabolically inert ("spore-like")
Rigid outer membrane with extensive disulphide cross-linking
Survives environmental exposure and transmission

Reticulate Body (RB)

Diameter: 800-1000 nm
Replicative, intracellular form
Metabolically active
Lacks rigid outer membrane structure
Cannot survive outside host cells

The Intracellular Life Cycle

Stage	Duration	Process
1. Attachment	0-2 hours	EB binds to host epithelial cells via OmcB protein and heparan sulphate proteoglycans
2. Internalisation	2-4 hours	Entry via receptor-mediated endocytosis; prevents phagolysosomal fusion
3. Primary Differentiation	4-12 hours	EB transforms into RB within the nascent inclusion
4. Replication	12-36 hours	RB undergoes binary fission; 8-12 hour doubling time
5. Secondary Differentiation	36-48 hours	RBs transform back into EBs
6. Release	48-72 hours	Cell lysis or extrusion releases 100-1000 EBs per inclusion

Exam Detail: Molecular Mechanisms of Immune Evasion

C. trachomatis employs sophisticated strategies to evade host defences:

Prevention of Phagolysosomal Fusion: The Type III secretion system injects effector proteins (Inc proteins) into the inclusion membrane that redirect vesicular trafficking away from the lysosomal pathway.
Acquisition of Host Nutrients: The inclusion intercepts Golgi-derived vesicles containing sphingomyelin and cholesterol, hijacking host lipid metabolism. [6]
Inhibition of Apoptosis: Chlamydial proteins block host cell apoptosis pathways, maintaining cellular viability during the replication phase.
Antigenic Variation: Major outer membrane protein (MOMP) undergoes antigenic variation, limiting the effectiveness of antibody-mediated immunity.
Persistent Forms: Under stress conditions (interferon-gamma exposure, nutrient deprivation, beta-lactam antibiotics), RBs can enter a non-replicative but viable persistent state, reactivating when conditions improve.

Why Beta-Lactams Fail

C. trachomatis possesses a unique cell envelope that renders beta-lactam antibiotics ineffective:

Factor	Mechanism	Clinical Implication
Minimal Peptidoglycan	Atypical cell wall lacks conventional peptidoglycan structure	Penicillins and cephalosporins cannot target cell wall synthesis
Intracellular Location	Organism resides within membrane-bound inclusions	Antibiotics must penetrate host cell membrane and inclusion membrane
Persistence	Beta-lactams induce persistent forms rather than killing	Apparent treatment failure with reactivation

Effective Antibiotic Classes:

Tetracyclines (doxycycline): Inhibit 30S ribosomal protein synthesis; excellent intracellular penetration
Macrolides (azithromycin): Inhibit 50S ribosomal protein synthesis; concentrate in phagocytes
Fluoroquinolones (moxifloxacin): DNA gyrase inhibition; reserved for complicated cases

Pathogenesis of Tubal Damage

The immunopathology of chlamydial infection, rather than direct tissue destruction, drives the development of tubal scarring: [7]

Acute Phase (Days to Weeks)

Chlamydial infection triggers robust Th1-type immune response
IFN-gamma production drives intracellular killing but also collateral tissue damage
Neutrophil and macrophage infiltration causes acute inflammation
IL-1 and TNF-alpha release amplifies inflammatory response

Chronic/Repeated Infection Phase

Chlamydial heat shock protein 60 (cHSP60) shares homology with human HSP60
Cross-reactive immune responses target both chlamydial and host tissue
Fibroblast activation drives collagen deposition and scar formation
Tubal epithelium destroyed; ciliated cells replaced by fibrous tissue
Luminal adhesions and fimbrial agglutination prevent ovum transport

Clinical Pearl: The Paradox of Immunity: The immune response that clears chlamydial infection is the same response that causes tissue damage. Women with strong Th1 responses clear infection effectively but may develop more severe scarring. This immunopathogenic mechanism complicates vaccine development.

3. Epidemiology

Global Burden

C. trachomatis infection represents a major global public health challenge with significant geographic and demographic variations: [1,8]

Region	Estimated Prevalence	Key Features
Global	129 million new cases/year (WHO 2020)	Most common bacterial STI
Europe	2.5 million cases/year	Rising incidence despite screening
United Kingdom	218,095 diagnoses (2019)	49% of all STI diagnoses
United States	1.8 million cases (2019)	Highest among 15-24 year olds
Australia	100,775 cases (2019)	Highest in remote Indigenous communities

Risk Factors

Demographic Risk Factors

Factor	Relative Risk	Evidence
Age less than 25 years	3-5x higher prevalence	Cervical ectopy, risk behaviours [9]
Female sex	Higher detection rates	Biological susceptibility, screening bias
Black ethnicity (UK/US)	3-5x higher prevalence	Healthcare access disparities
Low socioeconomic status	2x higher risk	Education, healthcare access
Sexual orientation (MSM)	Higher rectal infection rates	Anatomical site of exposure

Behavioural Risk Factors

Behaviour	Association	Mechanism
New sexual partner in past 3 months	Strongly associated	Exposure to untested/untreated individuals
Multiple concurrent partners	Dose-response relationship	Increased transmission probability
Inconsistent condom use	5-10x higher risk	Direct mucosal exposure
Substance use (alcohol/drugs)	Associated	Impaired judgment, risk-taking
Commercial sex work	High prevalence	Multiple partners, economic factors

Screening Recommendations

United States Preventive Services Task Force (USPSTF) 2021 [10]

Population	Recommendation	Grade
Sexually active women less than 25 years	Annual screening	Grade B
Women ≥25 years with risk factors	Screen based on risk	Grade B
Pregnant women less than 25 years	Screen at first prenatal visit	Grade B
Pregnant women ≥25 years with risk factors	Screen at first prenatal visit	Grade B
Men	Insufficient evidence for routine screening	Grade I
MSM	At least annual screening (all sites of exposure)	Clinical consensus

UK National Chlamydia Screening Programme (NCSP)

Component	Specification
Target population	Sexually active under-25s
Screening interval	Annually or on partner change
Settings	GP surgeries, pharmacies, sexual health clinics, online postal testing
Coverage target	2,300 diagnoses per 100,000 15-24 year olds

CDC Screening Recommendations 2021 [11]

Annual screening for all sexually active women less than 25 years
Annual screening for MSM at all exposed anatomical sites
Screening at first prenatal visit for pregnant women less than 25 years
Consider screening sexually active young men in high-prevalence settings

Evidence Debate: The Screening Paradox: Despite widespread screening programmes, chlamydia prevalence in the UK has not declined significantly. Possible explanations include:

Treatment with azithromycin: Lower microbiological cure rates (especially rectal infection) compared to doxycycline may permit ongoing transmission
"Arrested immunity" hypothesis: Early treatment prevents development of natural immunity, increasing susceptibility to reinfection
Core group dynamics: Transmission concentrated in high-risk networks not reached by current screening approaches
Partner notification gaps: Only 0.6 contacts treated per index case on average

Current research is evaluating whether screening strategies should shift from individual-level to network-based approaches. [12]

4. Clinical Presentation

Male Presentations

Urethritis (Non-gonococcal Urethritis - NGU)

Chlamydia causes 30-50% of NGU cases. [13] Clinical features:

Feature	Frequency	Characteristics
Urethral discharge	50-75%	Clear to mucopurulent; less purulent than gonococcal
Dysuria	40-60%	Burning/stinging on micturition
Meatal irritation	30-40%	Itching at urethral meatus
Asymptomatic	25-50%	Detected only on screening

Comparison with Gonococcal Urethritis:

Feature	Chlamydial NGU	Gonococcal Urethritis
Incubation	7-21 days	2-5 days
Discharge quality	Mucoid/mucopurulent	Frankly purulent, yellow-green
Discharge volume	Scanty to moderate	Profuse
Dysuria severity	Mild to moderate	Severe
Gram stain	No organisms seen	Gram-negative intracellular diplococci

Epididymo-orchitis

Chlamydia (and gonorrhoea) cause most cases of acute epididymitis in men less than 35 years: [14]

Feature	Clinical Finding
Age distribution	Peak incidence 15-35 years
Presentation	Unilateral scrotal pain, swelling over 1-2 days
Examination	Tender, swollen epididymis (posterior to testis)
Prehn's sign	Relief on elevation (unreliable - do not use to exclude torsion)
Cremasteric reflex	Usually present (absent in torsion)
Systemic features	Low-grade fever, may have associated urethritis

Clinical Pearl: The Testicular Torsion Rule: In any acute scrotum, testicular torsion must be excluded first. If clinical uncertainty exists, urgent Doppler ultrasound (or surgical exploration if unavailable within 6 hours) is mandatory. Never assume epididymitis without investigation in the acute setting.

Age-Based Aetiology of Epididymitis:

Age Group	Primary Pathogen	Secondary Pathogens
less than 35 years	C. trachomatis, N. gonorrhoeae	E. coli (if insertive anal sex)
> 35 years	E. coli, Pseudomonas	Enterobacteriaceae
Post-instrumentation	E. coli, Enterococcus	Pseudomonas

Proctitis

Rectal chlamydial infection occurs in MSM practicing receptive anal intercourse:

Serovar	Clinical Syndrome	Features
D-K	Mild proctitis or asymptomatic	Minimal symptoms; rectal discomfort, discharge
L1-L3 (LGV)	Severe proctocolitis	Rectal pain, tenesmus, bloody mucoid discharge, ulceration

Red Flag - LGV Proctitis: Any MSM presenting with severe proctitis symptoms (bloody discharge, tenesmus, rectal pain) requires urgent LGV testing. Untreated LGV proctitis can cause rectal strictures and permanent damage. [15]

Female Presentations

Cervicitis

The cervix is the primary site of chlamydial infection in women:

Feature	Finding	Frequency
Symptoms	May be asymptomatic	70-80%
Vaginal discharge	Mucopurulent	30-50%
Post-coital bleeding	Friable ectropion	20-30%
Intermenstrual bleeding	Cervical inflammation	15-20%
Dysuria	Concurrent urethritis	20-30%

Speculum Examination Findings:

Mucopurulent cervical discharge at os
Friable cervical ectropion (bleeds on contact with swab)
Cervical oedema and erythema

Urethritis

May occur with or without cervical infection:

Dysuria (often diagnosed as "sterile pyuria")
Frequency
Negative midstream urine culture

Clinical Pearl: The "Recurrent UTI" Trap: Young women with recurrent dysuria and negative urine cultures ("sterile pyuria") should be tested for chlamydia and gonorrhoea. Empirical UTI treatment without STI screening represents a missed diagnostic opportunity.

Pelvic Inflammatory Disease (PID)

Ascending infection causing upper genital tract involvement: [16]

Clinical Features:

Symptom/Sign	Frequency	Significance
Lower abdominal pain	95%	Cardinal symptom
Abnormal vaginal discharge	75%	Mucopurulent
Cervical motion tenderness	70%	"Chandelier sign"
Adnexal tenderness	65%	Unilateral or bilateral
Fever > 38.3C	30%	Indicates severe PID
Deep dyspareunia	50%	May be presenting complaint

CDC Clinical Criteria for PID Diagnosis:

Minimum criteria (low threshold for diagnosis):

Cervical motion tenderness OR
Uterine tenderness OR
Adnexal tenderness

Additional supportive criteria:

Oral temperature > 38.3C
Mucopurulent cervical discharge
Abundant WBCs on saline microscopy
Elevated CRP or ESR
Laboratory confirmation of cervical infection

Severity Grading:

Grade	Features	Management
Mild	Mobile adnexae, no peritonism, afebrile	Outpatient antibiotics
Moderate	Fever, elevated inflammatory markers, tubo-ovarian mass less than 8cm	Consider admission
Severe	Peritonism, tubo-ovarian abscess > 8cm, failed outpatient therapy	Inpatient IV antibiotics

Long-term Consequences of PID

The sequelae of PID represent the major public health burden of chlamydial infection: [3,17]

Complication	Risk After 1 PID Episode	Risk After 3+ Episodes
Tubal factor infertility	8-12%	40-54%
Ectopic pregnancy	6-10x increased risk	Higher with each episode
Chronic pelvic pain	18%	40-50%
Recurrent PID	20-25%	Cumulative

Fitz-Hugh-Curtis Syndrome (Perihepatitis)

Feature	Details
Pathogenesis	Ascending infection via paracolic gutter to liver capsule
Presentation	Right upper quadrant pain mimicking cholecystitis
Examination	RUQ tenderness, may have pleuritic component
Laparoscopy	"Violin string" adhesions between liver capsule and anterior abdominal wall
Association	10-15% of PID cases

Pharyngeal Chlamydia

Feature	Details
Prevalence	1-2% general population; up to 10% in MSM
Symptoms	Usually asymptomatic; rarely sore throat
Significance	Reservoir for transmission via oral sex
Treatment	Doxycycline effective (unlike pharyngeal gonorrhoea)
Testing	Throat swab NAAT if oral exposure history

Lymphogranuloma Venereum (LGV)

LGV is caused by the invasive L1-L3 serovars and follows a distinct clinical course: [15]

Stage 1: Primary Lesion (Days 3-30)

Small, painless papule or ulcer at inoculation site
Often unnoticed due to location and brief duration
Heals spontaneously within 1 week

Stage 2: Secondary Stage (Weeks 2-6)

Inguinal Syndrome (genital inoculation):

Painful inguinal lymphadenopathy (buboes)
Unilateral in 2/3 cases
Nodes become fluctuant and may rupture (sinuses)
Groove sign: Enlarged nodes above and below inguinal ligament

Anorectal Syndrome (rectal inoculation - common in MSM):

Severe haemorrhagic proctocolitis
Rectal pain, tenesmus, bloody mucoid discharge
May mimic inflammatory bowel disease
Perirectal lymphadenopathy (internal - not visible)

Stage 3: Tertiary Stage (Late)

Genital elephantiasis (lymphatic obstruction)
Rectal strictures
Rectovaginal fistulae
Esthiomene (chronic genital ulceration)

Neonatal Infections

Vertical transmission occurs during vaginal delivery through an infected birth canal: [18]

Ophthalmia Neonatorum

Feature	Details
Onset	5-14 days after birth
Presentation	Purulent conjunctival discharge, lid swelling
Differential	Gonococcal ophthalmia (earlier onset, more severe)
Complications	Corneal scarring if untreated; less severe than gonococcal
Treatment	Systemic azithromycin or erythromycin (topical inadequate)

Chlamydial Pneumonia of Infancy

Feature	Details
Onset	1-3 months of age
Clinical triad	Afebrile + Staccato cough + Bilateral infiltrates
Staccato cough	Short, sharp, repetitive ("machine gun") inspiratory cough
CXR	Bilateral interstitial infiltrates, hyperinflation
Laboratory	Peripheral eosinophilia (distinctive feature)
Treatment	Oral erythromycin or azithromycin x 14 days

Reactive Arthritis (Sexually Acquired - SARA)

Previously known as Reiter's syndrome, SARA follows chlamydial (or other enteric) infection: [19]

Classic Triad:

Urethritis - "Can't pee"
Conjunctivitis - "Can't see"
Arthritis - "Can't climb a tree"

Feature	Details
Timing	1-4 weeks post-infection
Joint pattern	Asymmetric oligoarthritis; large joints (knee, ankle)
HLA association	HLA-B27 positive in 60-80%
Duration	3-12 months; recurrence in 50%
Skin manifestations	Keratoderma blennorrhagica (palms/soles); Circinate balanitis (penis)

Pathogenic Mechanism:

Chlamydial antigens (particularly cHSP60) persist in joint synovium
Molecular mimicry with host HLA-B27 molecules
Cross-reactive T-cell responses attack synovial tissue
Joint fluid culture negative (sterile arthritis)

Adult Inclusion Conjunctivitis

Feature	Details
Serovars	D-K (not trachoma serovars A-C)
Mechanism	Autoinoculation from genital secretions
Presentation	Chronic follicular conjunctivitis, mucopurulent discharge
Duration if untreated	Months to years
Treatment	Systemic doxycycline (topical inadequate)

5. Trachoma

Trachoma, caused by serovars A, B, Ba, and C, is the leading infectious cause of preventable blindness globally: [20]

Epidemiology

Statistic	Value
Endemic countries	44 countries
At-risk population	142 million people
Blind from trachoma	1.9 million people
Trichiasis requiring surgery	2.5 million people

Transmission

Person-to-person via infected ocular secretions
Fomites (shared towels, cloths)
Eye-seeking flies (Musca sorbens)
NOT sexually transmitted

Natural History

Active Trachoma (Childhood)

Follicular conjunctivitis
Intense inflammation with papillae
Limbal follicles

Cicatricial Trachoma (Repeated Infection) 4. Conjunctival scarring (Arlt's line) 5. Entropion (inward turning of eyelid) 6. Trichiasis (eyelashes abrade cornea) 7. Corneal opacity and blindness

WHO SAFE Strategy

Component	Intervention
Surgery	Trichiasis surgery to prevent blindness
Antibiotics	Mass drug administration (azithromycin)
Facial cleanliness	Hygiene education
Environmental improvement	Water, sanitation, fly control

6. Diagnosis

Nucleic Acid Amplification Tests (NAATs)

NAATs are the gold standard for chlamydia diagnosis, having replaced culture: [21]

Parameter	Performance
Sensitivity	95-99%
Specificity	> 99%
Turnaround time	1-3 days (24 hours with PCR)
Detects	Chlamydial DNA/RNA (viable and non-viable organisms)

Approved Sample Types:

Population	First-Choice Sample	Alternative
Women	Self-taken vulvovaginal swab	Endocervical swab, urine
Men	First-catch urine (FCU)	Urethral swab
Rectal exposure	Rectal swab	-
Pharyngeal exposure	Pharyngeal swab	-

First-Catch Urine Protocol

Step	Instruction
1	Patient should not urinate for at least 1 hour before test
2	Collect first 20-30ml of voided urine
3	Do NOT collect midstream sample (this washes away urethral organisms)
4	Common error: Sending MSU for STI screening = false negative

Self-Taken Vulvovaginal Swabs

Evidence demonstrates equivalent sensitivity to clinician-collected specimens:

Step	Instruction
1	Wash hands
2	Insert swab 2-3 inches (5cm) into vagina
3	Rotate swab against vaginal walls for 10-15 seconds
4	Place swab in transport tube and seal

Clinical Pearl: Self-Sampling Preference: Studies show patients prefer self-sampling, and uptake of testing increases when self-sampling is offered. Self-taken vulvovaginal swabs are now recommended over clinician-collected samples for routine screening.

Testing Windows and Timing

Scenario	Recommendation
Minimum testing window	14 days post-exposure for reliable result
Immediate post-exposure	Test for baseline (may have pre-existing infection); repeat at 14 days
Negative test at day 3	Does not exclude infection - repeat at 14 days
Test of cure timing	5 weeks post-treatment (avoid false positive from persistent DNA)

LGV Testing

Standard NAATs detect chlamydia but cannot distinguish LGV from non-LGV serovars:

Scenario	Testing Protocol
Rectal chlamydia in MSM	Reflex LGV genotyping on all positive samples
Severe proctitis symptoms	Request LGV genotyping specifically
Inguinal buboes	LGV serotyping essential
Genital ulcer + lymphadenopathy	Consider LGV in differential

Point-of-Care Tests

Rapid chlamydia tests are available but have limitations:

Parameter	Performance
Sensitivity	80-85% (lower than NAAT)
Specificity	95-99%
Time	30-90 minutes
Role	Resource-limited settings; same-day treatment decisions

7. Management

The Azithromycin-to-Doxycycline Shift

International guidelines shifted from single-dose azithromycin to doxycycline as first-line therapy based on superior microbiological cure rates, particularly for rectal infection: [22,23]

Evidence Base:

Trial/Meta-analysis	Azithromycin Cure Rate	Doxycycline Cure Rate	Difference
Kong et al. 2014 (rectal)	83%	99%	-16%
Dukers-Muijrers 2015	84%	97%	-13%
Kissinger et al. 2016	80%	95%	-15%
Lau & Qureshi 2002 (urogenital)	97%	98%	-1%

Current Treatment Regimens

Uncomplicated Urogenital/Rectal Chlamydia

Regimen	Dose	Duration	Notes
Doxycycline (First-line)	100mg twice daily	7 days	Superior for rectal infection
Azithromycin (Alternative)	1g stat, then 500mg daily	1+2 days	If doxycycline contraindicated
Azithromycin (Extended)	1g stat alone	Single dose	Lower efficacy; consider if adherence concerns

Chlamydia in Pregnancy

Regimen	Dose	Duration	Notes
Azithromycin (First-line)	1g single dose	Stat	Safe in pregnancy (Category B)
Amoxicillin (Alternative)	500mg three times daily	7 days	Lower efficacy (~95%); needs TOC
Erythromycin (Alternative)	500mg twice daily	14 days	GI side effects limit tolerability

Doxycycline is contraindicated in pregnancy (teeth staining, bone effects in fetus)

Lymphogranuloma Venereum (LGV)

Regimen	Dose	Duration	Notes
Doxycycline (First-line)	100mg twice daily	21 days	Longer course for lymph node penetration
Erythromycin (Alternative)	500mg four times daily	21 days	If doxycycline contraindicated

Pelvic Inflammatory Disease

Setting	Regimen	Notes
Outpatient (Mild-Moderate)	Ceftriaxone 1g IM stat + Doxycycline 100mg BD x 14 days + Metronidazole 400mg BD x 14 days	Covers gonorrhoea, chlamydia, anaerobes
Inpatient (Severe)	Ceftriaxone 2g IV daily + Doxycycline 100mg IV/PO BD + Metronidazole 500mg IV BD	Switch to oral when clinically improved

Neonatal Chlamydial Infection

Condition	Regimen	Duration
Ophthalmia neonatorum	Erythromycin 50mg/kg/day in 4 divided doses	14 days
Chlamydial pneumonia	Erythromycin 50mg/kg/day in 4 divided doses	14 days
Alternative	Azithromycin 20mg/kg/day	3 days

Doxycycline Counselling Points

Issue	Advice
Oesophagitis risk	Take with full glass of water; remain upright for 30 minutes
Photosensitivity	Avoid prolonged sun exposure; use SPF 30+ sunscreen
Dairy interaction	Do not take with milk, calcium supplements, or antacids (chelation reduces absorption)
GI upset	Take with food (improves tolerability without reducing absorption)

Test of Cure

Population	TOC Recommendation	Timing
Routine uncomplicated	Not required	-
Pregnancy	Required	5 weeks post-treatment
LGV	Recommended	5 weeks post-treatment
Rectal infection	Recommended	5 weeks post-treatment
Persisting symptoms	Required	After completing treatment

Why 5 weeks? Chlamydial DNA may persist for up to 4 weeks post-treatment despite microbiological cure. Testing earlier risks false-positive NAAT results from non-viable DNA.

Sexual Abstinence Period

Treatment	Abstinence Period
Azithromycin 1g stat	7 days after dose
Doxycycline 7-day course	Until course completed
Partners	Must also abstain until their treatment completed

8. Partner Notification and Management

Contact Tracing Principles

Principle	Rationale
Look-back period	6 months (or last sexual contact if > 6 months ago)
All partner types	Includes casual, regular, and anonymous contacts
All exposure sites	Genital, oral, and rectal contacts
Confidentiality	Index patient identity not disclosed to contacts

Partner Notification Methods

Method	Process	Advantages
Patient referral	Index patient informs partners directly	Patient autonomy; high acceptance
Provider referral	Health advisor contacts partners	Ensures notification when patient unable
Contract referral	Patient agrees to notify; provider follows up if not done	Compromise approach
Anonymous notification	SMS/email with clinic code	Removes need for direct conversation

Expedited Partner Therapy (EPT)

Aspect	Details
Definition	Providing treatment to partners without prior medical evaluation
Mechanism	Index patient given extra prescription/medication to give to partner
Evidence	Reduces reinfection rates by 20% [24]
Legal status (UK)	Not standard practice; prescribing without consultation raises medicolegal issues
Legal status (US)	Legal in most states; CDC-recommended
Concerns	Allergy risk, missed diagnoses in partner, no counselling

Clinical Pearl: The "Ping-Pong" Effect: Treating the index patient without simultaneously treating sexual partners leads to reinfection within weeks. Partner notification and simultaneous treatment is essential for successful cure.

Patient Notification Script

Provide patients with language to use when informing partners:

"I've been diagnosed with an infection called chlamydia. It's very common and easily treated with antibiotics, but you could have it without knowing. It's important that you get tested this week, even if you feel fine. I've already been treated, so once you're treated too, we'll be fine."

9. Special Populations

Pregnancy

Concern	Recommendation
Screening	First prenatal visit; repeat in third trimester if high-risk
Treatment	Azithromycin 1g stat (first-line)
Contraindicated	Doxycycline (teratogenic - teeth staining, bone effects)
Fluoroquinolones	Contraindicated (cartilage damage)
TOC	Required at 5 weeks post-treatment
Neonatal risk	50-70% transmission rate during vaginal delivery

HIV Co-infection

Consideration	Details
Increased susceptibility	HIV+ individuals have higher chlamydia acquisition risk
Increased transmission	Chlamydia increases HIV viral shedding; enhances transmission
Treatment	Same regimens as HIV-negative individuals
Drug interactions	Check doxycycline and azithromycin against antiretroviral regimen
Partner testing	HIV testing of all partners essential

Men Who Have Sex with Men (MSM)

Consideration	Recommendation
Testing sites	Urine, rectal swab, and pharyngeal swab (all sites of exposure)
LGV screening	All rectal chlamydia positives should have LGV genotyping
Frequency	At least annual screening; 3-monthly if PrEP or high-risk
Rectal treatment	Doxycycline preferred (higher rectal cure rate than azithromycin)

Adolescents

Consideration	Details
Confidentiality	Gillick competence; can consent without parental knowledge if mature minor
Screening	Highest prevalence age group; opportunistic screening essential
Barriers	Stigma, fear of disclosure, lack of service awareness
Approach	Youth-friendly services; online/postal testing options

10. Mycoplasma genitalium - The Emerging Challenge

When chlamydia treatment "fails," consider Mycoplasma genitalium: [25]

Clinical Features

Feature	M. genitalium	C. trachomatis
Urethritis	Yes (10-20% of NGU)	Yes (30-50% of NGU)
Cervicitis	Yes	Yes
PID	Emerging evidence	Established
Treatment	Resistance-guided	Standard regimens

When to Suspect M. genitalium

Persistent urethritis after chlamydia treatment
Recurrent symptoms despite partner treatment
Negative chlamydia and gonorrhoea tests with ongoing symptoms

Treatment

Scenario	Regimen
Macrolide-sensitive	Doxycycline 100mg BD x 7 days, then Azithromycin 1g stat + 500mg daily x 3 days
Macrolide-resistant	Moxifloxacin 400mg daily x 7-14 days
Pre-treatment resistance testing	Recommended where available to guide therapy

11. Complications Summary

Acute Complications

Complication	Presentation	Management
Bartholin's abscess	Painful vulval swelling	Incision & drainage; antibiotics
Tubo-ovarian abscess	Fever, adnexal mass, severe pain	IV antibiotics; drainage if no response
Epididymal abscess	Scrotal swelling, fluctuance	Drainage; IV antibiotics
Perihepatitis	RUQ pain (Fitz-Hugh-Curtis)	Standard PID treatment

Chronic Complications

Complication	Mechanism	Prevention
Tubal factor infertility	Fallopian tube scarring/occlusion	Early treatment; screening
Ectopic pregnancy	Tubal damage preventing uterine implantation	Early treatment; screening
Chronic pelvic pain	Pelvic adhesions	Early treatment; screening
Rectal strictures	LGV scarring	LGV detection; prolonged treatment

Infertility Risk Quantification

Scenario	Tubal Factor Infertility Risk
1 episode of PID	8-12%
2 episodes of PID	20-23%
3+ episodes of PID	40-54%
Severe/hospitalized PID	Higher than mild
Chlamydia without clinical PID	May still cause subclinical damage

12. Prevention and Vaccine Development

Prevention Strategies

Strategy	Effectiveness	Notes
Condom use (consistent)	90%+ reduction in transmission	Requires correct and consistent use
Screening programmes	Population-level reduction in complications	Cost-effective; targets under-25s
Partner notification	Prevents reinfection and onward transmission	0.6 partners treated per case (UK average)
Behavioural interventions	Variable	Education; risk reduction counselling

Vaccine Development

Despite decades of research, no chlamydia vaccine is licensed: [26]

Challenge	Details
Natural immunity	Weak and short-lived; reinfection common
Immunopathology	Vaccine-induced immunity may worsen disease (historical concern from trachoma trials)
Intracellular lifestyle	Antibodies less effective against intracellular pathogens
Animal models	Limited relevance to human infection

Current Research:

CTH522 vaccine (MOMP-based): Phase 2 trials ongoing
Multi-subunit vaccines: Targeting cHSP60, PmpD, and other antigens
Mucosal delivery: Nasal/vaginal administration to induce local immunity

13. Viva Preparation

Opening Statement

"Chlamydia trachomatis infection is the most common bacterial sexually transmitted infection worldwide, caused by an obligate intracellular Gram-negative bacterium. It is characterised by its largely asymptomatic nature in 70-80% of women and 50% of men, which facilitates ongoing transmission. The organism exists in three serovar groups: urogenital serovars D-K causing cervicitis, urethritis, and PID; LGV serovars L1-L3 causing invasive lymphatic disease; and trachoma serovars A-C causing ocular disease. Diagnosis is by NAAT testing, and first-line treatment is now doxycycline 100mg twice daily for 7 days, which has replaced azithromycin due to superior efficacy, particularly for rectal infection."

Key Examinable Points

Topic	Key Points
Microbiology	Obligate intracellular; EB (infectious) vs RB (replicative); 48-72 hour cycle
Serovars	D-K (urogenital), L1-L3 (LGV), A-C (trachoma)
Screening	USPSTF Grade B: all sexually active women less than 25 annually
Treatment shift	Doxycycline > Azithromycin (especially rectal: 99% vs 83% cure)
PID sequelae	12% infertility after 1 episode; 54% after 3 episodes
LGV	21-day doxycycline; suspect in MSM with severe proctitis
Neonatal	Ophthalmia (5-14 days); Pneumonia (1-3 months, staccato cough, afebrile, eosinophilia)

Common Examiner Questions

Q: Why has doxycycline replaced azithromycin as first-line treatment?

A: "Meta-analyses demonstrated that doxycycline achieves significantly higher microbiological cure rates than azithromycin, particularly for rectal infection where doxycycline achieves 99% cure versus 83% for azithromycin. This 16% difference is clinically important for transmission control. For urogenital infection, the difference is smaller but still favours doxycycline at 98% versus 97%."

Q: A 22-year-old woman has recurrent 'UTIs' with sterile pyuria. What would you consider?

A: "Sterile pyuria in a young, sexually active woman should prompt consideration of urethritis due to sexually transmitted pathogens, particularly Chlamydia trachomatis and Neisseria gonorrhoeae. I would take a sexual history, perform vulvovaginal swab for chlamydia and gonorrhoea NAAT testing, and also consider Mycoplasma genitalium as an emerging cause of urethritis."

Q: How would you counsel a pregnant woman diagnosed with chlamydia?

A: "I would explain that chlamydia is common and easily treatable, but treatment is important to prevent transmission to the baby during delivery, which can cause eye infection or pneumonia. I would prescribe azithromycin 1g as a single dose, which is safe in pregnancy. Doxycycline is contraindicated due to effects on fetal teeth and bones. I would recommend partner notification and treatment, abstinence until 7 days post-treatment, and arrange a test of cure at 5 weeks."

Critical Errors to Avoid

Error	Why It Fails
Recommending azithromycin for rectal chlamydia	Inferior cure rate (83% vs 99%)
Using doxycycline in pregnancy	Teratogenic (teeth staining)
Testing for TOC at 2 weeks	False positive from persistent DNA
Forgetting partner notification	Reinfection will occur
Missing LGV in MSM proctitis	Requires 21-day treatment, not 7 days
Treating neonatal chlamydia with topical drops alone	Systemic treatment required

14. References

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Senior Editor: Dr. N. Goyal (Infectious Diseases) Guideline Check: BASHH 2015, CDC 2021, USPSTF 2021, European Guidelines 2016-2018 verified. Last Updated: January 2025 Topic: 773/1071

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