What are the organisms and how do they differ?
Neisseria gonorrhoeae is an obligate human pathogen, a Gram-negative diplococcus that targets columnar and transitional epithelium (urethra, endocervix, rectum, pharynx, conjunctiva). Chlamydia trachomatis is a Gram-negative, obligate intracellular bacterium that replicates only inside host cells and has a biphasic life cycle. The two coexist often: over 20% of people with gonorrhoea also have chlamydia.
| Feature | N. gonorrhoeae | C. trachomatis |
|---|---|---|
| Gram / morphology | Gram-negative diplococci, intracellular in neutrophils (polymorphs) | Gram-negative but not seen on Gram stain; elementary body and reticulate body |
| Growth | Needs selective media (modified Thayer-Martin, Martin-Lewis, NYC); oxidase positive | Obligate intracellular; difficult to culture; needs cell culture (e.g. McCoy cells) |
| Attachment | Pili and Opa proteins (opacity-associated), both undergo phase and antigenic variation | Elementary body taken up by host cells |
| Immune evasion | Antigenic variation; IgA1 protease | Replicates inside host cells |
| Serovars | Not typed clinically | A, B, Ba, C: trachoma; D–K: genital and neonatal infection; L1–L3: lymphogranuloma venereum |
| Discharge | Thick, purulent, usually more voluminous | White, grey or clear, often only after stripping or in the morning |
| Treatment | Ceftriaxone (cephalosporin) | Doxycycline or azithromycin |
How do gonococci and chlamydiae cause disease?
Gonococcus: pili first attach the organism to epithelium, and Opa proteins also help attachment. Binding of pili to host complement receptor 3 produces membrane ruffles; the bacteria enter in macropinosomes and multiply, penetrating to the basement membrane. Gonococcal lipopolysaccharide stimulates TNF production, which damages cells. Strains that resist serum killing can disseminate through blood. In men a strong inflammatory response makes infection symptomatic; in women the gonococcus evades immunity during uncomplicated cervical infection, so most women are asymptomatic, but ascent into the uterus and tubes causes marked inflammation.
Chlamydia has two forms. The elementary body (EB) is infectious but metabolically inactive and is taken up by the host cell. Inside, it becomes the metabolically active reticulate body (RB), which divides within an intracytoplasmic inclusion using host energy and amino acids, then reorganises into new EBs that infect further cells. The organism targets squamocolumnar cells of the endocervix and upper tract in women, and conjunctiva, urethra and rectum in both sexes.
What are the clinical features in men and women?
| Site / group | Gonorrhoea | Chlamydia |
|---|---|---|
| Men | 56–87% asymptomatic; symptoms in 2–14 days: mucopurulent urethral discharge, dysuria; epididymitis, orchitis, prostatitis, penile lymphangitis, urethral stricture | Urethritis (white, grey or clear discharge), epididymitis, prostatitis; about 1% of men with chlamydial urethritis develop reactive arthritis |
| Women | Up to 90% asymptomatic; cervicitis with mucopurulent discharge, dysuria, intermenstrual bleeding; Bartholin gland abscess; PID in 10–20% | Over 80% asymptomatic or mild; mucopurulent cervicitis with easily induced bleeding in a minority; PID |
| Rectum / pharynx | Often asymptomatic; proctitis (pain, bleeding, discharge) | Genital serovars usually silent; L1–L3 cause proctitis with rectal pain, discharge and bleeding |
| Eye | Gonococcal conjunctivitis (severe, purulent); ophthalmia neonatorum | Inclusion conjunctivitis; trachoma (A–C); neonatal conjunctivitis is the commonest neonatal chlamydial presentation |
| Newborn | Ophthalmia neonatorum from the birth canal | Conjunctivitis; pneumonia in 5–30% of infants of infected mothers (staccato cough, little fever, onset 4–12 weeks) |
- Disseminated gonococcal infection occurs in 0.5–3% of gonorrhoea: fever, arthritis–dermatitis syndrome, tenosynovitis, polyarthralgia; the knee is the commonest joint; endocarditis in 1–2% of DGI; meningitis rare. About half of confirmed cases have negative mucosal tests.
- Lymphogranuloma venereum (LGV) (L1–L3): a small, painless, stellate genital ulcer followed by inguinal lymphadenopathy, or severe proctocolitis.
- Fitz-Hugh-Curtis syndrome (perihepatitis): right upper quadrant or pleuritic pain with normal liver enzymes, from either organism in PID.
- About 40% of PID overall is caused by gonorrhoea (StatPearls); chlamydia ascending to the upper tract also causes PID.
How are gonorrhoea and chlamydia diagnosed in the laboratory?
| Test | Gonorrhoea | Chlamydia |
|---|---|---|
| NAAT | Optimal method; over 95% sensitive and specific; best for pharynx and rectum; vulvovaginal swab is the preferred specimen | Gold standard for urogenital infection; vaginal swab (women) or first-catch urine (men) |
| Gram stain | Male urethral smear with PMNs and intracellular Gram-negative diplococci is diagnostic (specificity about 99%; sensitivity about 95% symptomatic, 80% or less asymptomatic; only 40–60% for endocervix). Not recommended from pharynx or rectum | Not useful |
| Culture | Modified Thayer-Martin, Martin-Lewis or NYC; oxidase-positive colonies plus Gram-negative diplococci give presumptive identification; needed for susceptibility testing and in suspected treatment failure or DGI | Cell culture only; difficult and rarely done |
| Cytology / Giemsa | Not used | Intracytoplasmic inclusions in Giemsa-stained scrapings; positive in 90% of neonatal and 50% of adult inclusion conjunctivitis; poor sensitivity on cervical cytology |
| Point of care | Results in 30–90 minutes; sensitivity 97–100% | Not applicable |
What are the complications and sequelae?
| Complication | Notes |
|---|---|
| Pelvic inflammatory disease | Ascending infection: endometritis, salpingitis, tubo-ovarian abscess; scarring leads to tubal infertility, ectopic pregnancy and chronic pelvic pain; repeated chlamydial infection causes tubal scarring |
| Perihepatitis | Fitz-Hugh-Curtis syndrome, with adhesions between liver capsule and diaphragm or abdominal wall |
| Male genital | Epididymo-orchitis, prostatitis, urethral stricture (gonorrhoea) |
| Reactive arthritis | Chlamydia: urethritis, arthritis, uveitis; formerly Reiter syndrome |
| Disseminated disease | Gonorrhoea: arthritis-dermatitis, tenosynovitis, endocarditis, meningitis |
| Pregnancy and newborn | PROM, preterm birth, low birth weight; neonatal ophthalmia (both) and neonatal chlamydial pneumonia |
| Trachoma and LGV | Serovars A–C (leading infectious cause of blindness); L1–L3 for lymphogranuloma venereum |
How are gonorrhoea and chlamydia treated — WHO, India (NACO) and other guidance?
Gonococcal resistance to penicillin and ciprofloxacin is established and azithromycin resistance is growing, so ceftriaxone is the mainstay. WHO advises that local resistance data should guide the choice. Always compare which guideline a question cites.
| Source | First choice | Alternatives / remarks |
|---|---|---|
| WHO 2024 | Ceftriaxone 1 g IM single dose (also for pregnant women) | If unavailable or refused: cefixime 800 mg orally with test of cure. If test of cure not possible or oropharyngeal infection: cefixime 800 mg plus azithromycin 2 g. For cephalosporin allergy or resistance: spectinomycin 2 g IM or gentamicin 240 mg IM, each plus azithromycin 2 g |
| CDC (as summarised in StatPearls) | Ceftriaxone 500 mg IM single dose if under 150 kg (1 g if 150 kg or more); add doxycycline 100 mg twice daily for 7 days if chlamydia not excluded (azithromycin 1 g in pregnancy) | Cefixime 800 mg only if ceftriaxone is unavailable. Severe cephalosporin allergy: gentamicin 240 mg IM plus azithromycin 2 g. Pharyngeal infection needs test of cure at 7–14 days |
| India: NHM / NACO syndromic kit | Kit 1 (grey) for urethral discharge, cervicitis, ano-rectal discharge and painful scrotal swelling: azithromycin 1 g plus cefixime 400 mg, both single dose, covering gonorrhoea and chlamydia together | Lower abdominal pain / PID: Kit 6 (yellow) cefixime 400 mg stat, metronidazole 400 mg twice daily and doxycycline 100 mg twice daily for 14 days. Vaginal discharge alone: Kit 2 (secnidazole plus fluconazole) |
| Situation | Treatment |
|---|---|
| Uncomplicated genital, anorectal, oropharyngeal | Doxycycline 100 mg twice daily for 7 days. If doxycycline unavailable or adherence a serious concern: azithromycin 1 g single dose. Further alternatives: erythromycin 500 mg four times daily for 7 days, ofloxacin 200–400 mg twice daily for 7 days, tetracycline 500 mg four times daily for 7 days |
| Pregnant or breastfeeding | Azithromycin 1 g single dose (strong recommendation). If unavailable: amoxicillin 500 mg three times daily or erythromycin 500 mg four times daily, each for 7 days. Doxycycline, tetracycline and ofloxacin are contraindicated |
| LGV (StatPearls, quoting guidelines) | Doxycycline 100 mg twice daily for 21 days, or azithromycin 1 g weekly for 3 weeks |
| Neonatal conjunctivitis or pneumonia | Oral erythromycin 50 mg/kg/day in 4 divided doses for 14 days; azithromycin 20 mg/kg/day for 3 days is an alternative. Infantile hypertrophic pyloric stenosis risk with erythromycin and azithromycin, mainly in the first 2 weeks |
- Complicated gonorrhoea (PID, epididymitis, proctitis): ceftriaxone 500 mg with oral doxycycline 100 mg twice daily for 7 days (CDC, via StatPearls).
- Disseminated gonococcal infection: ceftriaxone 1 g every 24 hours IM or IV; may switch to an oral agent 24–48 hours after clear improvement; total 7 days. Meningitis or endocarditis: ceftriaxone 1–2 g IV every 12–24 hours.
- Gonococcal conjunctivitis (adult): ceftriaxone 1 g IM single dose, with saline eye lavage considered.
- Partners, abstinence and follow-up: treat partners, abstain from sex until treated (1 week after starting for chlamydia); retest at 3 months; for chlamydia StatPearls advises verification of cure about 3 weeks after treatment and retesting at 3 months.
What about pregnancy, newborns and screening?
- Pregnancy: gonococcal infection causes low birth weight and transmission to the newborn; chlamydia raises PROM, PPROM and preterm delivery. Screen at the first antenatal visit in high-risk women; treat chlamydia with azithromycin, not doxycycline. Pregnant women given ceftriaxone should be watched for allergic reactions, premature delivery and PROM (WHO).
- Neonatal prophylaxis against gonococcal ophthalmia: CDC recommends erythromycin 0.5% eye ointment for all newborns, since gonococcal conjunctivitis affects about 0.3 per 1,000 live births. WHO (as listed in StatPearls) recommends one of these topical agents for all newborns: tetracycline 1% eye ointment, erythromycin 0.5% ointment, povidone iodine 2.5% solution, silver nitrate 1% solution or chloramphenicol 1% ointment.
- Newborn of an infected mother, no signs: ceftriaxone 20–50 mg/kg IV or IM single dose (maximum 250 mg), with caution in hyperbilirubinaemia.
- Screening: annually for sexually active women under 25 and for older women at increased risk, with repeat testing 3 months after treatment.
Other STI topics are covered in STI syndromic management kits, syphilis stages and serology and vaginitis: BV, candida and trichomonas.
What are the common exam traps?
- Chlamydia does not appear on Gram stain. A urethral smear with intracellular diplococci is gonorrhoea.
- Treat both when in doubt: the NHM kit 1 combines azithromycin plus cefixime for exactly this reason; WHO's cefixime-plus-azithromycin 2 g option keeps the 2 g azithromycin to cover chlamydia.
- Doxycycline is contraindicated in pregnancy; use azithromycin 1 g. Erythromycin is the neonatal drug.
- Serovars: D–K genital, A–C trachoma, L1–L3 LGV.
- Fitz-Hugh-Curtis syndrome has normal liver enzymes.
- Pharyngeal gonorrhoea needs ceftriaxone (cefixime is less reliable) and a test of cure; Gram stain is not used on pharyngeal or rectal samples.