Lucan · Conditions

Epididymo-orchitis

Australian guidance: No AU epididymo-orchitis diagnosis/management guideline (the Australian STI Management Guidelines or an eTG genital-infections topic) is captured in this repo. AMH Online (Jan 2026) drug monographs for ceftriaxone, doxycycline, azithromycin, cefalexin, amoxicillin-clavulanate, and trimethoprim each list epididymo-orchitis as an indication with individual AU dosing

1. Definition and epidemiology

Epididymo-orchitis is inflammation of the epididymis (epididymitis), often extending to involve the testis (orchitis), most commonly caused by ascending bacterial infection from the urethra or bladder. It is the most common cause of the acute scrotum outside childhood and adolescence, where testicular torsion predominates, and represents the critical differential that Australian junior clinicians must confidently distinguish from torsion, because missing torsion risks testicular loss while unnecessary surgical exploration for a patient who actually has epididymo-orchitis carries its own morbidity. Aetiology is strongly age- and behaviour-stratified. In sexually active men under 35 years, Chlamydia trachomatis is the most frequent pathogen, with Neisseria gonorrhoeae accounting for a smaller but clinically important minority, particularly in men reporting condomless sex with new or casual partners; these sexually transmitted organisms remain the leading cause in sexually active men of any age. In men over 35 years without high STI risk, and in men of any age who have engaged in insertive anal intercourse or undergone recent urethral instrumentation or catheterisation, enteric gram-negative organisms — chiefly Escherichia coli and Proteus species — predominate, reflecting their origin in bladder outflow dysfunction (benign prostatic hyperplasia, urethral stricture) rather than sexual transmission. Less common but important causes include mumps orchitis (paramyxovirus), occurring in around 20 to 25 percent of post-pubertal males with mumps, now rare in Australia given high measles-mumps-rubella (MMR) coverage on the National Immunisation Program but still seen in outbreaks and under-vaccinated cohorts, and tuberculous epididymitis, a rare but important cause of chronic, indolent epididymal swelling that should be considered in patients from high TB-prevalence countries or with a history of renal tuberculosis.

2. Pathophysiology

The dominant mechanism of bacterial epididymo-orchitis is retrograde ascent of pathogens from the urethra, through the vas deferens, into the epididymis. In sexually acquired disease, Chlamydia trachomatis and Neisseria gonorrhoeae colonise the urethral epithelium following sexual contact and spread proximally along the vas deferens, seeding the epididymal head initially before extending to the tail and, in more severe cases, to the testis itself by direct contiguous spread. In older men or those with bladder outflow obstruction, retrograde ascent of infected urine — driven by raised intraluminal pressure from prostatic enlargement, urethral stricture, or an indwelling catheter — carries enteric organisms along the same anatomical route. The resulting acute inflammatory response produces epididymal oedema, neutrophilic infiltration, and increased blood flow (hyperaemia), which is what scrotal Doppler ultrasound detects as a discriminating feature from the reduced or absent flow of testicular torsion. Non-ascending causes follow different routes: mumps orchitis results from haematogenous seeding of the testis during the viraemic phase of systemic paramyxovirus infection, producing a lymphocytic interstitial orchitis with oedema constrained by the non-distensible tunica albuginea — this pressure effect underlies the ischaemic tubular atrophy seen in a substantial proportion of affected testes. Tuberculous epididymitis typically arises from haematogenous seeding during primary infection with later reactivation, or from descending spread from renal tuberculosis via the ureter, bladder, and vas deferens, producing caseating granulomatous inflammation that classically causes a firm, nodular, beaded thickening of the vas deferens (Robbins Ch 21).

3. Clinical presentation and diagnostic criteria

Epididymo-orchitis typically presents with unilateral scrotal pain and swelling that develops gradually over hours to several days, in contrast to the sudden, dramatic onset of testicular torsion. Associated lower urinary tract or urethral symptoms — dysuria, urethral discharge, frequency — are common but may be entirely absent despite confirmed chlamydial or gonococcal infection, so their absence must not be used to exclude epididymo-orchitis. On examination, the epididymis is tender, swollen, and indurated, typically palpable as a distinct structure posterolateral to the testis in early disease; as inflammation progresses the epididymis and testis become difficult to distinguish as separate structures, and a reactive hydrocele may develop. Fever and systemic upset are more common than in torsion, and pyuria on urinalysis is a supportive finding that reflects the underlying urethral or urinary infective process.

Two bedside signs are classically taught as discriminators from torsion: Prehn sign (relief of pain with manual elevation of the affected hemiscrotum, said to favour epididymo-orchitis) and the cremasteric reflex (elicited by stroking the medial thigh and observing ipsilateral testicular elevation; classically preserved in epididymo-orchitis and lost in torsion). Both are worth eliciting, but neither is sufficiently sensitive or specific to be used in isolation to rule torsion in or out — a positive Prehn sign or preserved cremasteric reflex should never on its own be used to defer urgent surgical assessment when the overall clinical picture is concerning for torsion. The more reliable discriminating pattern is the combination of gradual symptom onset, fever, pyuria, and infective risk factors (sexual activity, voiding dysfunction) against the sudden, severe, often exertion- or minor-trauma-triggered pain of torsion with a high-riding, transversely lying testis and an absent cremasteric reflex. When the clinical picture is equivocal, the default must be urgent urological or surgical assessment, because torsion is time-critical and testicular salvage falls sharply beyond approximately six hours of ischaemia.

4. Investigations and AU-specific cutoffs

No source captured in this repo addresses the diagnostic approach to suspected epididymo-orchitis. The first-pass urine versus MSU testing protocol, the STI screening panel, the urethral swab indication, and the role and limits of scrotal Doppler ultrasound were all stated as fact in the pre-grounding version of this note and attributed to the Australian STI Management Guidelines or the Melbourne Sexual Health Centre guidelines — neither of which is a file held in this repo (both were cited only as external URLs). None of it has been verified against a source actually read for this note, and it has been removed rather than restated with a caveat. Capture the Australian STI Management Guidelines' epididymo-orchitis page, or an eTG genital-infections topic covering epididymo-orchitis, before restating any of it.

5. Management

No source captured in this repo addresses risk-stratified empirical antibiotic selection, the review timeline, contact tracing windows, notification requirements, or the threshold for surgical exploration in suspected epididymo-orchitis. All of this was stated as fact in the pre-grounding version of this note and attributed to the two uncaptured guidelines named in Section 4 above; none of it traces to a file read for this note and it has been removed rather than restated with a caveat. Capture the Australian STI Management Guidelines' epididymo-orchitis page, or an eTG genital-infections topic covering epididymo-orchitis, before restating any admission, empirical-choice, contact-tracing, or follow-up content.

6. Pharmacology and AU PBS notes

The captured sources for this section are six individual AMH drug monographs, not a syndromic epididymo-orchitis guideline — each confirms that the named drug is indicated for epididymo-orchitis and gives that drug's own AU dose, but none of them is the guideline decision of which drug to choose first, or in what combination, for a given patient.

Sexually acquired epididymo-orchitis: - Ceftriaxone (AMH, sources/amh/anti-infectives/antibacterials/ceftriaxone.md) lists "Sexually acquired epididymo-orchitis (with doxycycline)" as an indication. Its dosing sits under "Gonococcal infection – Urethritis, cervicitis, epididymo-orchitis and PID": "Adult, IM/IV 250–500 mg as a single dose (for epididymo-orchitis, give for 1–5 days; seek advice from local STI clinic)." This differs from the pre-grounding version of this note, which stated a single stat dose only — AMH's own text says epididymo-orchitis specifically may need dosing "for 1–5 days," and advises seeking local STI clinic advice rather than giving one fixed national regimen. IM reconstitution uses lidocaine 1%. - Doxycycline (AMH, sources/amh/anti-infectives/antibacterials/doxycycline.md) lists "Sexually acquired epididymo-orchitis (with ceftriaxone)" as an indication but has no epididymo-orchitis-specific dosing line. Its general chlamydial/non-gonococcal genital infection dose is "oral 100 mg twice daily for 1–3 weeks depending on the site and severity of the infection" — a range that includes, but is not fixed at, the 14 days previously stated. Children <8 years are excluded (tooth discolouration/enamel dysplasia risk); doxycycline is "unlikely to stain teeth in children <8 years when used short term." - Azithromycin (AMH, sources/amh/anti-infectives/antibacterials/azithromycin.md) lists chlamydial infections generally as an indication. Its specific "Chlamydial infection, gonococcal genital infection" dose is "oral 1 g as a single dose" — the source does not describe the two-stage regimen (1 g immediately, then a further 1 g at one week) previously stated in this note; that additional dose has been removed as unsourced.

Enteric-organism epididymo-orchitis: - Cefalexin (AMH, sources/amh/anti-infectives/antibacterials/cefalexin.md) lists "Epididymo-orchitis (urinary tract source)" as an indication but gives no epididymo-orchitis-specific dose or duration; its general adult dose is 250 mg every 6 hours or 500 mg every 6–12 hours (maximum 4 g daily). - Amoxicillin with clavulanic acid (AMH, sources/amh/anti-infectives/antibacterials/amoxicillin-clavulanic-acid.md) lists "Epididymo-orchitis (urinary tract source)" as an indication but likewise gives no epididymo-orchitis-specific dose; its general adult oral dose is 500–875 mg every 12 hours for "5–10 days or longer, depending on the infection." - Trimethoprim (AMH, sources/amh/anti-infectives/antibacterials/trimethoprim.md) lists "Epididymo-orchitis (urinary tract source)" as an indication with a dedicated dosing line: "Oral, 300 mg once daily for 2 weeks" — this is the one drug in this section with an AMH dose specific to epididymo-orchitis, and it is not mentioned in the pre-grounding version of this note.

Not yet verified against a primary source, and removed from this note rather than kept with a caveat: norfloxacin or any other fluoroquinolone for epididymo-orchitis (no fluoroquinolone AMH monograph is captured in this repo) and the associated TGA fluoroquinolone safety-caution claim; the specific 500 mg/875-125 mg/14-day figures for ceftriaxone, cefalexin, and amoxicillin-clavulanate insofar as they were stated as THE guideline regimen rather than as one dose within the ranges AMH actually gives; and the tuberculous-epididymitis anti-tuberculous drug list (rifampicin, isoniazid, pyrazinamide, ethambutol) and mumps-orchitis supportive-care/notifiability claims, neither of which traces to a captured source. Capture an AMH or eTG anti-tuberculous therapy topic, a fluoroquinolone AMH monograph, and the Australian STI Management Guidelines' epididymo-orchitis page before restating any of this.

7. Complications and monitoring

Abscess formation complicates a minority of cases of severe or inadequately treated epididymo-orchitis, presenting as a fluctuant, increasingly tender scrotal mass with persisting or worsening fever despite antibiotics; ultrasound confirms the diagnosis and surgical drainage is usually required alongside continued antibiotics. Testicular infarction is a rare but serious complication of severe epididymo-orchitis, arising from venous congestion and septic thrombophlebitis of the pampiniform plexus compressing arterial inflow within the non-distensible tunica albuginea; it is one of the findings Doppler ultrasound is specifically used to detect and may necessitate orchiectomy if the testis is non-viable. Infertility and subfertility are recognised long-term consequences: bacterial epididymo-orchitis can cause epididymal duct fibrosis and obstruction, particularly with recurrent, bilateral, or inadequately treated infection, producing obstructive azoospermia; mumps orchitis causes testicular atrophy in around 60 percent of affected testes, and while fertility is reduced in only around one-quarter of men after unilateral mumps orchitis, the minority who develop bilateral disease carry a substantially higher risk (around two-thirds) of impaired fertility. Chronic epididymal or testicular pain (chronic orchialgia) can persist for months after apparently successful antibiotic treatment as a consequence of residual fibrosis and low-grade inflammation, and may warrant analgesia review, urology referral, or, rarely, spermatic cord block or epididymectomy in refractory cases.

Ongoing monitoring includes clinical review at 4 to 5 days to confirm response, completion of the full antibiotic course even if symptoms resolve early, retesting for chlamydia and gonorrhoea reinfection at 3 months in confirmed STI cases, and confirmation that partner notification has occurred. Any patient whose pain worsens, who develops a new fluctuant mass, or who remains febrile beyond 48 to 72 hours of appropriate antibiotics should be reassessed urgently for abscess or infarction, and any patient in whom the initial diagnosis of epididymo-orchitis is thrown into doubt — particularly if pain escalates rather than improves — should be reassessed for torsion.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.