Chlamydia is the most frequently reported notifiable disease in the United States, with the CDC recording 1.65 million cases in 2022. Caused by the obligate intracellular bacterium Chlamydia trachomatis, the infection is largely silent — roughly 70% of cervical infections in women and 50% of male urethral infections produce no symptoms — which is why women under 25 are screened annually regardless of symptoms.
Chlamydia infection (ICD-10: A56) is a sexually transmitted bacterial infection caused by Chlamydia trachomatis serovars D through K, which selectively infect columnar epithelium of the urogenital tract, rectum, pharynx, and conjunctiva. The organism is an obligate intracellular pathogen with a unique biphasic lifecycle: the elementary body (infectious form) enters epithelial cells, transforms into the metabolically active reticulate body that divides within an inclusion, and re-differentiates into elementary bodies that are released to infect adjacent cells. This intracellular biology explains the slow tempo of symptoms (1-3 weeks after exposure), the prolonged carriage, and the need for antibiotics that achieve intracellular concentrations. Clinical presentations include urethritis, cervicitis, proctitis, pharyngitis, conjunctivitis, lymphogranuloma venereum (LGV — caused by serovars L1-L3), neonatal conjunctivitis and pneumonia, and the post-infectious reactive arthritis syndrome.
key facts
Prevalence
1.65 million US cases in 2022 (CDC); rate ~495 per 100,000 — most reported notifiable disease
Demographics
Women account for 64% of US cases; rate in women 15-24 is over 4,000 per 100,000
Avg. age
Highest incidence in adults 15-24 years; rare in adults over 35
Global cases
~129 million new global infections per year (WHO 2020); 4.0% global prevalence in women 15-49
Specialist
Infectious Disease
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How you might notice it
The key symptoms of Chlamydia Infection are: Most infections cause no symptoms — 70% of cervical infections in women and 50% of male urethral infections are silent, persisting for months without notice., Mild, often clear or whitish urethral discharge in symptomatic men, appearing 1-3 weeks after exposure and easily mistaken for a minor irritation., Dysuria (burning on urination) in men and women, typically less intense than the dysuria of gonorrhea or urinary tract infection., Increased vaginal discharge in women, sometimes mucopurulent, often noticed alongside intermenstrual bleeding or post-coital bleeding., Lower abdominal or pelvic pain in women — a warning sign of ascension to pelvic inflammatory disease and reason for urgent evaluation., Dyspareunia (painful intercourse) and cervical motion tenderness on bimanual exam, both features of cervicitis or early PID., Rectal pain, mucus discharge, tenesmus, or bleeding in symptomatic rectal chlamydia, though most rectal infections are asymptomatic..
01Most infections cause no symptoms — 70% of cervical infections in women and 50% of male urethral infections are silent, persisting for months without notice.
02Mild, often clear or whitish urethral discharge in symptomatic men, appearing 1-3 weeks after exposure and easily mistaken for a minor irritation.
03Dysuria (burning on urination) in men and women, typically less intense than the dysuria of gonorrhea or urinary tract infection.
04Increased vaginal discharge in women, sometimes mucopurulent, often noticed alongside intermenstrual bleeding or post-coital bleeding.
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How it’s diagnosed
diagnosis
Diagnosis relies on nucleic acid amplification testing (NAAT), which has displaced culture and antigen detection due to sensitivity exceeding 95% and specificity exceeding 99% across all anatomic sites. Specimen choice depends on patient and site: first-catch urine in men, vaginal or endocervical swab in women, and self- or clinician-collected pharyngeal and rectal swabs in MSM and in any patient with relevant exposure. CDC recommends extragenital (pharyngeal and rectal) testing in MSM and in any patient who reports oral or anal sex. Self-collected swabs are accurate and acceptable to most patients. Culture is now reserved for medicolegal cases (sexual assault evaluation), suspected antimicrobial treatment failure, and research; routine clinical management uses NAAT. Lymphogranuloma venereum requires identification of L1-L3 serovars through PCR genotyping or specific LGV-typing assays, available through state public health labs. Every chlamydia diagnosis should trigger bundled testing for gonorrhea, syphilis, HIV, and hepatitis B and C at the same visit, since 10-30% of patients have a second concurrent STI. CDC recommends annual screening of all sexually active women under 25, women over 25 with risk factors, MSM at all anatomic sites every 3-6 months, and pregnant individuals at the first prenatal visit. Repeat NAAT 3 months after treatment is recommended for all patients to detect reinfection, the dominant cause of "recurrent" chlamydia. Test of cure is not routinely needed for urogenital chlamydia treated with doxycycline but is recommended in pregnancy, persistent symptoms, suspected non-adherence, and after alternative regimens. Public health reporting is mandatory in all US states.
Key tests
01
Nucleic acid amplification test (NAAT)Detects C. trachomatis DNA or RNA in urine, vaginal, endocervical, pharyngeal, or rectal specimens. Sensitivity 96-99%, specificity >99%. The standard first-line test recommended by CDC.
02
Extragenital NAAT (pharyngeal and rectal)Detects rectal and pharyngeal infections that are missed on genital-only testing. CDC recommends in MSM and anyone with relevant exposure, since missed extragenital infections drive ongoing transmission.
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Treatment & cost
medical treatments
✓Doxycycline 100 mg PO twice daily × 7 days
✓Azithromycin 1 g PO single dose
✓Doxycycline 100 mg PO twice daily × 21 days (LGV)
✓Amoxicillin 500 mg PO three times daily × 7 days (pregnancy alternative)
surgical options
Drainage of fluctuant LGV buboSymptom relief in 85-90%; recurrence uncommon with adequate antibiotic course.
Drainage of tubo-ovarian abscessResolution in 80-90% of cases with combined antibiotic and drainage approach.
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Causes & risk factors
known causes
Sexual transmission of Chlamydia trachomatis
The dominant cause. Transmission occurs during vaginal, anal, or oral sex with an infected partner. Per-act transmission probability is approximately 10% per exposure for men and women, varying with site and partner viral load.
Vertical transmission at delivery
Infants born to infected mothers acquire the organism through the birth canal in 30-50% of cases, producing conjunctivitis 5-14 days later or pneumonia at 4-12 weeks. Maternal screening at the first prenatal visit and again in the third trimester (in those at risk) prevents most cases.
Autoinoculation to the eye
Genital secretions transferred to the eye by hand contact or sexual practices cause adult inclusion conjunctivitis. The same organism causes trachoma in resource-limited settings via fly transmission and repeated reinfection.
Asymptomatic transmission
Because 50-70% of infected people have no symptoms, transmission occurs from people who do not know they are infected. This is the central epidemiologic feature driving CDC's recommendation for universal annual screening of sexually active women under 25.
Persistent reservoirs from inadequate treatment
Single-dose azithromycin (the previous first-line) cures only 80-85% of rectal chlamydia, leaving a reservoir for re-emergence. Doxycycline 100 mg twice daily for 7 days cures rectal infection in 95% of cases, which drove the 2021 CDC switch to doxycycline as first-line.
risk factors
Age under 25non-modifiable
Over 60% of US chlamydia cases occur in adults under 25. Cervical ectropion (more susceptible columnar epithelium) in young women, higher partner change rates, and inconsistent condom use drive the pattern.
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Living with it
01Use latex or polyurethane condoms consistently and correctly during vaginal, anal, and oral sex — reduces per-act transmission by 50-90%
02Annual chlamydia screening for all sexually active women under 25, plus older women and pregnant patients with risk factors
03Sexually active MSM should receive triple-site (urine, throat, rectal) NAAT every 3-6 months
04Notify and refer for treatment all sexual contacts within the prior 60 days of a positive diagnosis — expedited partner therapy where legal
05Discuss doxycycline post-exposure prophylaxis (doxy-PEP) with a clinician if you are MSM or a transgender woman at high STI risk — reduces incident chlamydia by ~70%
06Prenatal screening at the first prenatal visit and again in the third trimester for at-risk pregnant individuals
recommended foods
•Standard balanced nutrition supports immune recovery during treatment
•Adequate hydration during oral antibiotic courses
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When to seek help
why see an infectious disease
Infectious disease consultation is warranted in suspected LGV, severe or treatment-refractory pelvic inflammatory disease, complicated neonatal disease, pregnancy with macrolide or amoxicillin intolerance, and recurrent infection despite adequate treatment. Most uncomplicated cases are managed by primary care and sexual health clinics according to CDC algorithms.
Uncomplicated urogenital chlamydiaCervicitis or urethritis with or without symptoms. The most common presentation, treated with 7 days of doxycycline.
Rectal chlamydiaAnal canal infection from receptive anal sex. Often asymptomatic; symptomatic disease presents with pruritus, mucopurulent discharge, tenesmus, or bleeding. Cure rates with single-dose azithromycin are lower than at other sites, which contributed to the 2021 switch to doxycycline as first-line.
Pharyngeal chlamydiaThroat infection from oral sex; almost always asymptomatic. CDC recommends testing in MSM but not routinely at other sites.
Lymphogranuloma venereum (LGV)Caused by serovars L1-L3. Three-stage illness: small painless primary lesion, painful regional lymphadenitis with fluctuant buboes, and chronic strictures or fistulas. Endemic in resource-limited settings; resurgence in MSM in Europe and North America since 2003.
Neonatal chlamydial conjunctivitis and pneumoniaVertical transmission during vaginal delivery from an infected mother. Conjunctivitis appears 5-14 days after birth; pneumonia 4-12 weeks.
Reactive arthritis (Reiter syndrome)Post-infectious arthritis 1-3 weeks after acute infection, especially in HLA-B27 carriers. The classic triad — urethritis, conjunctivitis, and arthritis — was traditionally attributed to chlamydia.
Living with Chlamydia Infection
Timeline
Urethral and vaginal symptoms typically resolve within 5-10 days of starting doxycycline. Sexual activity should be avoided for 7 days after completing the regimen and until partners are treated. PID pain and fever resolve over 3-7 days with appropriate antibiotics. LGV inguinal lymphadenopathy responds over 2-4 weeks of doxycycline; bubo resolution may take 2-3 months. Retest at 3 months for reinfection; test of cure is not routinely needed for doxycycline-treated urogenital cases but is recommended in pregnancy and after alternative regimens.
Lifestyle
01Abstain from sex for 7 days after completing treatment (or 7 days after single-dose azithromycin) and until partners have been treated
02Take doxycycline on a full stomach with a large glass of water and remain upright for 30 minutes to prevent esophagitis
03Avoid prolonged sun exposure during doxycycline therapy; the drug causes photosensitivity
04Return for retesting at 3 months — the most common cause of recurrent chlamydia is reinfection, not treatment failure
05Notify any new sexual contacts of your diagnosis so they can be tested
06Use condoms consistently with new or untested partners going forward
Daily management
01Take each dose of doxycycline at approximately 12-hour intervals on a full stomach
Choosing a doctor
Choose a clinician familiar with the CDC 2021 STI Treatment Guidelines, with access to NAAT testing at all relevant anatomic sites (urine, vaginal, pharyngeal, rectal), who prescribes doxycycline-first (with appropriate exceptions), and who integrates bundled STI screening at every visit. Sexual health clinics typically offer rapid testing, partner notification support, and expedited partner therapy where legal.
Yes. A 7-day course of doxycycline 100 mg twice daily cures 95-100% of uncomplicated urogenital, rectal, and pharyngeal chlamydia. Pregnant patients receive single-dose azithromycin 1 g instead. Reinfection from a new exposure is common (15-25% within 12 months) but is distinct from treatment failure.
What are the symptoms of chlamydia?▾▴
Most chlamydia infections cause no symptoms — 70% of cervical infections in women and 50% of urethral infections in men are silent. When symptoms occur, they include mild discharge, burning urination, post-coital bleeding, pelvic pain in women, and testicular pain in men, typically 1-3 weeks after exposure.
How is chlamydia transmitted?▾▴
Chlamydia spreads through vaginal, anal, or oral sex with an infected partner. It can also pass from mother to baby during vaginal delivery. It does not spread through casual contact, toilet seats, swimming pools, or shared utensils.
How is chlamydia tested?▾▴
Nucleic acid amplification testing (NAAT) on urine, vaginal, endocervical, pharyngeal, or rectal specimens is the standard test. Sensitivity exceeds 95%. Self-collected swabs are accurate. Testing at all relevant anatomic sites is recommended for MSM and anyone with relevant exposure.
Why did CDC change from azithromycin to doxycycline?▾▴
Single-dose azithromycin cures urogenital chlamydia in 95% of cases but only 80-85% of rectal infections. Randomized trials showed doxycycline 100 mg twice daily for 7 days cures rectal chlamydia in 95% of cases. CDC updated the 2021 STI Treatment Guidelines to make doxycycline first-line for all sites.
Can chlamydia go away on its own?▾▴
No. Untreated chlamydia may persist for months without symptoms, but the bacterium remains and continues to transmit. Asymptomatic infection can ascend in women to cause pelvic inflammatory disease and infertility. Without antibiotics, infection can persist for over a year.
Can men get chlamydia without symptoms?▾▴
Yes. About 50% of male urogenital chlamydia infections cause no symptoms, and almost all rectal and pharyngeal infections in MSM are asymptomatic. CDC recommends triple-site (urine, throat, rectal) screening every 3-6 months in sexually active MSM and routine screening of partners of diagnosed patients.
Does chlamydia affect fertility?▾▴
Untreated chlamydia in women can ascend to cause pelvic inflammatory disease and tubal scarring. Tubal-factor infertility risk is approximately 12% after one PID episode, 25% after two, and 50% after three. Prompt antibiotic treatment substantially reduces this risk. Annual screening of sexually active women under 25 prevents most cases.
How long should I wait before having sex after chlamydia treatment?▾▴
Abstain from sex for 7 days after starting doxycycline (or 7 days after single-dose azithromycin) and until all sexual partners have completed treatment. Resuming earlier risks reinfection of yourself or transmission to partners. Retest at 3 months for reinfection, and use condoms with new or untested partners going forward.
Should my partner be treated?▾▴
Yes. All sexual contacts within the prior 60 days should be tested and treated for chlamydia. Many US states allow expedited partner therapy — a prescription for the partner without a clinic visit. Health departments can assist with anonymous partner notification when needed.
Can chlamydia come back?▾▴
Yes. Successful treatment does not produce lasting immunity. Reinfection rates are 15-25% within 12 months in high-risk populations, driven mainly by an untreated partner or a new exposure. Retesting at 3 months is CDC standard for all patients diagnosed with chlamydia.
What happens if chlamydia is left untreated?▾▴
Untreated chlamydia can cause pelvic inflammatory disease, tubal scarring, ectopic pregnancy, infertility in women, and epididymitis in men. Both sexes face increased HIV acquisition risk. Reactive arthritis can develop 1-3 weeks after acute infection. Lymphogranuloma venereum can produce chronic strictures and fistulas if untreated.
Is chlamydia an STI or STD?▾▴
Both terms apply. Chlamydia is a sexually transmitted infection (STI), which becomes a sexually transmitted disease (STD) when symptoms or complications develop. The CDC and most current guidelines prefer "STI" to reduce stigma and acknowledge that most infections are asymptomatic. Chlamydia is the most reported notifiable infection in the US.
Can chlamydia cause urinary tract infection symptoms?▾▴
Chlamydia can cause urethritis with burning urination, especially in men. The dysuria is typically milder than a urinary tract infection and often accompanies discharge. Urine NAAT distinguishes chlamydia from bacterial UTI. In sexually active patients with sterile pyuria, chlamydia should be tested.
Can chlamydia affect newborns?▾▴
Yes. Infants born to infected mothers acquire the organism in 30-50% of vaginal deliveries, producing conjunctivitis 5-14 days after birth and afebrile pneumonia at 4-12 weeks. Maternal prenatal screening and treatment prevent most cases. Treatment for neonatal disease is oral erythromycin or azithromycin for 14 days.
What is lymphogranuloma venereum?▾▴
Lymphogranuloma venereum (LGV) is a more invasive form of chlamydia caused by serovars L1-L3. It produces a small painless primary lesion, painful inguinal lymphadenopathy with fluctuant buboes, and chronic strictures or fistulas if untreated. Treatment requires 21 days of doxycycline — three times the duration of standard chlamydia.
How much does chlamydia treatment cost?▾▴
Doxycycline costs USD 5-20 for a 7-day course as a generic. Most US sexual health clinics offer testing and treatment free regardless of insurance status. Single-dose azithromycin costs USD 5-15 as a generic. Total out-of-pocket cost is typically under USD 50; costs in India and other emerging markets are even lower.
Is there a vaccine for chlamydia?▾▴
No licensed vaccine exists for chlamydia as of 2026, though several candidates are in clinical trials. Prevention currently relies on barrier protection, screening, prompt treatment, and partner notification. The first Phase 2 chlamydia vaccine trial completed in 2023 showed immunogenicity, with Phase 3 trials anticipated.
When should I be screened for chlamydia?▾▴
CDC recommends annual screening for all sexually active women under 25, older women with risk factors, MSM at all three sites every 3-6 months, and pregnant individuals at the first prenatal visit. Anyone with new symptoms, a new partner, or a partner diagnosed with chlamydia should be tested.
Can I drink alcohol while taking doxycycline for chlamydia?▾▴
Moderate alcohol use is acceptable but excessive drinking can reduce doxycycline blood levels through enzyme induction and worsen gastric side effects. Avoid alcohol entirely if pelvic inflammatory disease is being treated and metronidazole is included — that combination causes a disulfiram-like reaction with nausea and flushing.
Does chlamydia cause back pain?▾▴
Lower back pain in women with chlamydia can signal pelvic inflammatory disease and warrants prompt evaluation. Reactive arthritis after chlamydia can cause sacroiliac joint pain, especially in HLA-B27 carriers. In men, ascending infection with epididymitis can cause flank or groin pain. Isolated upper back pain is not typical of chlamydia.
05Lower abdominal or pelvic pain in women — a warning sign of ascension to pelvic inflammatory disease and reason for urgent evaluation.
06Dyspareunia (painful intercourse) and cervical motion tenderness on bimanual exam, both features of cervicitis or early PID.
07Rectal pain, mucus discharge, tenesmus, or bleeding in symptomatic rectal chlamydia, though most rectal infections are asymptomatic.
08Right upper quadrant pain with normal liver enzymes (Fitz-Hugh-Curtis syndrome) — perihepatitis as a complication of PID.
09Painful, swollen testicle (epididymitis) in men with ascending infection, usually unilateral and developing 1-2 weeks after initial symptoms.
10Persistent inflamed conjunctiva with stringy mucoid discharge in adult inclusion conjunctivitis — autoinoculation from genital secretions or partner contact.
early warning signs
•Any new urethral or vaginal discharge in a sexually active person under 25
•Spotting or bleeding between periods or after sex in a young woman
•A new sexual partner with diagnosed chlamydia, gonorrhea, or other STI
•Persistent low-grade pelvic discomfort or pelvic pain after a recent unprotected sexual encounter
•Mild conjunctivitis with stringy mucoid discharge in a sexually active adult
● emergency signs
•Severe lower abdominal pain with fever and discharge — possible pelvic inflammatory disease or tubo-ovarian abscess requiring urgent evaluation
•Painful unilateral testicular swelling with fever — possible chlamydial epididymitis; rule out testicular torsion by ultrasound
•Acute right upper quadrant pain in a woman with pelvic infection — Fitz-Hugh-Curtis syndrome (perihepatitis)
•Severe groin pain with fluctuant lymph nodes in MSM — possible LGV with bubo formation requiring drainage and prolonged doxycycline
•Newborn 5-14 days old with red, sticky, discharging eyes — neonatal chlamydial conjunctivitis warrants oral erythromycin or azithromycin
•Infant 4-12 weeks old with afebrile staccato cough, tachypnea, and bilateral interstitial pneumonia on X-ray — chlamydial neonatal pneumonia
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Pelvic examination with cervical motion tenderness assessmentIdentifies pelvic inflammatory disease and cervicitis in women. PID minimum criteria require cervical, uterine, or adnexal tenderness with cervical discharge.
04
LGV-typing PCRIdentifies the L1-L3 serovars responsible for lymphogranuloma venereum, distinguishing them from non-LGV chlamydia at rectal sites. Affects treatment duration (3 weeks vs 1 week).
05
Bundled STI screeningTests for gonorrhea, syphilis, HIV, and hepatitis B and C at the same visit due to high co-infection rates.
06
Urine pregnancy test in women of reproductive agePregnancy alters treatment choice (avoid doxycycline; use azithromycin). Mandatory before treatment in any sexually active woman of reproductive age.
Outlook
With doxycycline 7-day therapy, the prognosis for uncomplicated urogenital, rectal, and pharyngeal chlamydia is excellent — microbiologic cure in 95-100% of cases. Single-dose azithromycin cures 95% of urogenital infections but only 80-85% of rectal infections, which is why doxycycline is now first-line. Pelvic inflammatory disease responds clinically in over 90% of cases with appropriate antibiotic therapy, but tubal scarring still develops in roughly 12% of women after a single PID episode, 25% after two episodes, and 50% after three. The corresponding rises in ectopic pregnancy (6-7 fold) and tubal-factor infertility are the dominant long-term consequences. Reactive arthritis, when it develops, peaks 1-3 weeks after the acute infection, is more common in HLA-B27 carriers, and resolves over 3-6 months in most cases; a minority become chronic. LGV strictures and fistulas are largely preventable with prompt 21-day doxycycline. Reinfection is the dominant cause of recurrence — 15-25% within 12 months in high-risk populations — and reflects ongoing exposure rather than antibiotic failure. The decisive prognostic factor at the population level is screening uptake: the more sexually active young women receive annual screening, the lower the PID and infertility burden.
New or multiple sexual partnersmodifiable
Each additional new partner in the past year approximately doubles infection probability. Concurrent partnerships drive transmission in network analyses.
Inconsistent condom usemodifiable
Consistent correct condom use reduces per-act transmission by 50-90%. Real-world adherence is variable; partial use provides partial protection.
Men who have sex with men (MSM)non-modifiable
MSM carry a disproportionate share of rectal and pharyngeal chlamydia, often asymptomatic. CDC recommends triple-site screening (urine, throat, rectal) every 3-6 months.
Prior chlamydia or other STImodifiable
Previous STI signals ongoing exposure pattern. Reinfection rates within 12 months are 15-25% in high-risk groups, particularly when partners are not treated.
Cervical ectropionnon-modifiable
Outward extension of cervical columnar epithelium, common in young women and oral contraceptive users. Provides more susceptible target tissue for chlamydial attachment.
HIV infectionnon-modifiable
Higher rates of pharyngeal and rectal chlamydia in HIV-positive patients; co-infection facilitates HIV transmission and acquisition.
Drug or alcohol use during sexmodifiable
Reduces consistent condom use and partner selectivity. Methamphetamine use in MSM is linked to higher chlamydia incidence in chemsex circuits.
foods to avoid
•Calcium-rich foods, antacids, and iron supplements within 2 hours of doxycycline — chelation reduces absorption
•Probiotic supplements within 2 hours of doxycycline — interferes with drug levels
•Alcohol during PID treatment if metronidazole is included — disulfiram-like reaction
07Neonatal chlamydial conjunctivitis (5-14 days postpartum) and pneumonia (4-12 weeks)
08Tubo-ovarian abscess requiring drainage in severe PID
02Drink at least 200 mL of water with each dose and remain upright for 30 minutes
03Avoid antacids, calcium, iron supplements, and dairy within 2 hours of each dose
04Use sunscreen and protective clothing while on doxycycline
05Notify your clinician if you develop severe abdominal pain, dysphagia, or new vaginal bleeding
06Mark your calendar for follow-up retesting at 3 months
Exercise
No specific restrictions for uncomplicated chlamydia. With pelvic inflammatory disease, rest until pain and fever resolve, then gradually return to normal activity. With reactive arthritis, avoid weight-bearing exercise on affected joints until inflammation settles.