Non-gonococcal Urethritis (Chlamydial Genital Infection)

NGU Definition

Diagnosis of exclusion (urethritis, gonococcus ruled out). C. trachomatis = COMMONEST cause (15-40%). Also: M. genitalium, U. urealyticum, T. vaginalis (see Bacterial Vaginosis/Trichomoniasis topic). Substantial minority = no organism found. This topic = C. trachomatis focus.

Organism

Obligate intracellular. CANNOT make own ATP (“energy parasite”) — why never cell-free cultured.

Biphasic developmental cycle:

EB (Elementary Body): small, metabolically INACTIVE, INFECTIOUS extracellular form (spore-like hardiness)
RB (Reticulate Body): larger, metabolically ACTIVE, replicates by binary fission INSIDE cytoplasmic vacuole/inclusion, NON-infectious

Cycle: EB attaches/enters → reorganizes to RB → RB multiplies in inclusion → reorganizes back to EB → cell ruptures/exocytoses → new EBs released. ~48-72hr cycle → explains more INDOLENT/slower symptom onset vs gonococcus’s acute presentation.

Serovars: A-C = trachoma (ocular, see Ocular topic). D-K = genital infections (this topic). L1-L3 = LGV (separate topic, more invasive syndrome despite same species).

Clinical Manifestations

Men: urethritis, SCANT mucoid/watery discharge, mild dysuria. MILDER than gonococcal → often missed/dismissed, delays care. Untreated → epididymitis.

Women: cervicitis, FREQUENTLY ASYMPTOMATIC (even more than gonococcal). Central epidemiological fact — MOST commonly reported bacterial STI in most countries (silent spread). PID: same ascending route as gonococcus, same downstream risks (infertility, ectopic pregnancy, chronic pelvic pain). Chlamydial PID = more indolent/less acute than gonococcal → EVEN MORE likely unrecognized until fertility complication.

Reactive arthritis (ex-Reiter syndrome): sterile post-infectious arthritis, triad w/ conjunctivitis+urethritis. Follows chlamydial genital infection, esp. HLA-B27+. IMMUNE-MEDIATED, not direct joint infection.

Neonatal infection (vaginal delivery, infected maternal cervix):

Neonatal conjunctivitis (inclusion conjunctivitis) — LATER than gonococcal ophthalmia (5-14 days vs first few days)
Neonatal pneumonia — even LATER (4-12 weeks), staccato cough, NO fever Differing timelines = useful clinical clue.

Fitz-Hugh-Curtis syndrome: perihepatitis (RUQ pain, “violin-string” liver-abdominal wall adhesions), direct/lymphatic spread from pelvic infection. Complication of ascending chlamydial (± gonococcal) PID.

Laboratory Diagnosis

NAAT = METHOD OF CHOICE (far outperforms culture, C. trachomatis can’t be cell-free cultured, needs specialized cell-culture — slow, rarely used outside research/medicolegal). Urine or self-collected swab. COMBINED PANEL with gonococcus typical (co-infection logic).

DFA + EIA (antigen): historical, superseded by NAAT sensitivity, used where NAAT unavailable.

Serology: NARROW role — NOT useful for acute genital infection diagnosis (can’t distinguish current vs past). Useful: LGV diagnosis specifically (see that topic), select fertility workups (past tubal damage suspicion).

Treatment

Azithromycin (single dose) or Doxycycline (1 week course) — BOTH 1st line, roughly equally effective. Azithromycin = practical adherence advantage (single dose/DOT settings). PARTNER TREATMENT ESSENTIAL regardless of symptom status (frequent asymptomatic infection) — treating only symptomatic partner sets up reinfection.

Prevention

Condoms, partner notification+treatment, ROUTINE SCREENING for sexually active young women (many countries) — reflects high asymptomatic rate + serious preventable reproductive consequences.

Defining Non-Gonococcal Urethritis

Non-gonococcal urethritis (NGU) is, by definition, a diagnosis of exclusion at the syndrome level — urethritis in which gonococcus has been ruled out — but in practice, Chlamydia trachomatis is by far the commonest identified cause, responsible for roughly 15–40% of cases in most series, followed by Mycoplasma genitalium, Ureaplasma urealyticum, and Trichomonas vaginalis (covered under Bacterial Vaginosis and Trichomoniasis); a substantial minority of NGU cases have no organism identified at all despite thorough testing. This topic focuses on C. trachomatis, the dominant and best-characterized cause.

The Organism

Chlamydia trachomatis is an obligate intracellular bacterium — genuinely unable to generate its own ATP, making it an “energy parasite” that depends entirely on the host cell for this purpose, which is exactly why it can never be grown on cell-free artificial media the way most other bacteria can. It has a genuinely distinctive biphasic developmental cycle, alternating between two structurally and functionally different forms: the elementary body (EB) — small, metabolically inactive, the infectious extracellular form, analogous to a bacterial spore in its environmental hardiness — and the reticulate body (RB) — larger, metabolically active, replicating by binary fission inside the host cell’s cytoplasmic vacuole (inclusion), but non-infectious itself. The cycle runs: EB attaches and enters the cell → reorganizes into an RB → RB multiplies repeatedly within the inclusion → RBs reorganize back into EBs → the cell ruptures (or the inclusion exocytoses), releasing new EBs to infect neighbouring cells. This full cycle takes roughly 48–72 hours, which is part of why chlamydial infection tends to be more indolent and slower to produce symptoms than gonococcus’s fast-onset, acute presentation.

C. trachomatis itself has multiple serovars grouped by the disease they cause: serovars A–C cause trachoma (ocular, covered under Ocular and Ear Infections), D–K cause the genital tract infections described here, and L1–L3 cause lymphogranuloma venereum (a genuinely more invasive syndrome, covered as its own topic given how different its clinical behaviour is from ordinary genital C. trachomatis infection despite sharing the same species).

Clinical Manifestations

In men: urethritis with typically scant, mucoid or watery discharge and mild dysuria — genuinely milder and less immediately obvious than gonococcal urethritis’s copious purulent discharge, which is exactly why chlamydial infection is so often missed or dismissed as trivial by the patient, delaying care. Untreated infection can ascend to cause epididymitis.

In women: cervicitis, frequently asymptomatic (even more so than gonococcal cervicitis) — this silent tendency is the central epidemiological fact about chlamydia, and is why it is the most commonly reported bacterial STI in most countries with STI surveillance, since silent infection persists and spreads undetected far more readily than a symptomatic one would. As with gonococcus, ascending untreated infection causes pelvic inflammatory disease, with the same downstream risks of infertility, ectopic pregnancy, and chronic pelvic pain — and because chlamydial PID tends to be more indolent/less acutely symptomatic than gonococcal PID, it is, if anything, even more likely to go unrecognized until a fertility complication brings it to light.

Reactive arthritis (formerly Reiter syndrome) — a sterile, post-infectious inflammatory arthritis, classically described alongside conjunctivitis and urethritis as a clinical triad — can follow chlamydial genital infection, particularly in HLA-B27-positive individuals, reflecting a genuine immune-mediated mechanism rather than direct joint infection by the organism.

Neonatal infection: acquired during vaginal delivery through an infected maternal cervix, causing neonatal conjunctivitis (inclusion conjunctivitis, typically presenting later than gonococcal ophthalmia neonatorum, at 5–14 days rather than the first few days of life) and neonatal pneumonia (presenting even later, at 4–12 weeks, with a characteristic staccato cough and absence of fever) — the differing, genuinely distinct timelines for these two chlamydia-related neonatal syndromes are themselves a useful clinical clue when working through a differential.

Fitz-Hugh-Curtis syndrome — perihepatitis (right-upper-quadrant pain and “violin-string” adhesions between the liver capsule and abdominal wall on direct visualization) from direct or lymphatic spread of pelvic infection to the liver capsule — is a recognized complication of ascending chlamydial (and occasionally gonococcal) PID.

Laboratory Diagnosis

NAAT (nucleic acid amplification test) is now the diagnostic method of choice by a wide margin, given C. trachomatis’s poor performance with older methods — it dramatically outperforms culture in sensitivity, and, since the organism is obligate intracellular and cannot be cultured on cell-free media at all, requires specialized cell-culture systems that are slow, technically demanding, and rarely used outside research/legal (e.g. medicolegal sexual-assault) settings today. NAAT can be run on urine or a self-collected vaginal/urethral swab, and is typically ordered as a combined panel with gonococcus testing, mirroring the same co-infection logic covered under Gonococcal Urethritis.

Direct fluorescent antibody (DFA) staining and enzyme immunoassay (EIA) for chlamydial antigen were historically used but have been substantially superseded by NAAT’s superior sensitivity, and are now used mainly where NAAT access is limited.

Serology has a genuinely narrow, specific role — it is not useful for diagnosing acute genital infection (since it cannot distinguish current from past infection, and takes time to become positive), but is used diagnostically for lymphogranuloma venereum specifically (see that topic) and in select fertility workups investigating suspected past tubal damage.

Treatment

Azithromycin (single oral dose) or doxycycline (a week-long course) are both first-line and essentially equally effective for uncomplicated genital chlamydial infection, with the single-dose azithromycin regimen having a real practical advantage for treatment adherence/directly observed therapy in settings where completing a multi-day course is a genuine concern. As with gonococcus, partner treatment is essential regardless of the partner’s symptom status, given how often the infection is asymptomatic in one or both partners — treating only the symptomatic partner while leaving an asymptomatic partner untreated simply sets up reinfection.

Prevention

Condom use, partner notification and treatment, and — in many countries — routine screening programmes for sexually active young women specifically, reflecting chlamydia’s high asymptomatic-infection rate and the serious, largely preventable long-term reproductive consequences of undetected, untreated disease.