Sexually transmitted infections — chlamydia, gonorrhoea, syphilis, treatment (eTG)

1. Definition and clinical relevance

Chlamydia, gonorrhoea, and syphilis are bacterial sexually transmitted infections (STIs) caused by Chlamydia trachomatis, Neisseria gonorrhoeae, and Treponema pallidum respectively. Globally, hundreds of millions of new curable STI cases occur annually, with chlamydia and gonorrhoea among the most prevalent. In Australia, rates of all three infections have risen substantially over the past decade, with syphilis re-emerging as a public health emergency, particularly in remote Aboriginal and Torres Strait Islander communities and among gay, bisexual, and other men who have sex with men (GBMSM). As an intern, you will encounter these infections across emergency, general medicine, gynaecology, and primary care settings. Missed diagnosis leads to pelvic inflammatory disease (PID), infertility, epididymo-orchitis, congenital syphilis, and facilitated HIV transmission.

2. Key values, thresholds, scoring systems

Chlamydia treatment (uncomplicated urogenital or rectal)

Gonorrhoea treatment (uncomplicated)

Syphilis staging and treatment

3. Approach: presentation and differential

Chlamydia

Most infections are asymptomatic, particularly in women. When symptomatic, men may present with urethral discharge or dysuria. Women may have mucopurulent cervical discharge, intermenstrual bleeding, or dyspareunia. Ascending infection causes PID (lower abdominal pain, cervical motion tenderness, adnexal tenderness or mass). Rectal infection causes proctitis. Reactive arthritis (urethritis, conjunctivitis, arthritis) is a recognised complication.

Gonorrhoea

Men more commonly develop symptomatic urethritis with purulent discharge and dysuria. Women are often asymptomatic or have cervicitis. Pharyngeal and rectal infection occur in GBMSM and others practising receptive oral or anal sex. Disseminated gonococcal infection presents with fever, migratory polyarthritis, and a characteristic pustular or haemorrhagic rash.

Syphilis

Primary syphilis produces a solitary, painless, indurated genital ulcer (chancre) 9-90 days after exposure. The ulcer is highly infectious and resolves spontaneously. Secondary syphilis appears weeks later with a generalised maculopapular rash (classically involving palms and soles), condylomata lata, mucous patches, and systemic symptoms including fever and lymphadenopathy. Latent syphilis is asymptomatic. Late syphilis causes gummatous, cardiovascular, and neurological disease. Neurological involvement can occur at any stage, not only late disease.

Key differentials for genital ulceration

1. Herpes simplex virus (HSV) - multiple painful vesicles/ulcers, most common
2. Primary syphilis - single painless indurated ulcer
3. Chancroid - painful ulcer with suppurative inguinal lymphadenopathy (rare in Australia)
4. Lymphogranuloma venereum (LGV) - mainly GBMSM, inguinal buboes
5. Donovanosis - granulomatous, seen in some remote Australian communities
6. Trauma or fixed drug eruption (non-infective)

Key differentials for urethral or vaginal discharge

1. Chlamydia
2. Gonorrhoea
3. Bacterial vaginosis (most common cause of vaginal discharge overall)
4. Candidiasis
5. Trichomonas vaginalis
6. Mycoplasma genitalium (non-gonococcal urethritis)

4. Investigations

Nucleic acid amplification testing (NAAT)

NAAT is the gold standard for both chlamydia and gonorrhoea. For asymptomatic screening, first-void urine (FVU) in males and self-collected vulvovaginal swabs (VVS) in females are preferred as they are non-invasive and highly sensitive. Self-collected VVS performs equivalently to clinician-collected specimens. FVU is less sensitive than VVS in females and should not be used as the sole specimen in women. GBMSM who practise receptive anal or oral sex require additional rectal and pharyngeal swabs for NAAT.

Gonorrhoea culture

Culture (urethral swab in males, endocervical swab in females, rectal and pharyngeal swabs) is required alongside NAAT whenever gonorrhoea is suspected, to allow antibiotic susceptibility testing given rising resistance patterns.

Syphilis serology

Screening uses a combination of treponemal (e.g. TPPA, EIA) and non-treponemal (e.g. RPR, VDRL) tests. RPR titre tracks disease activity and treatment response. A fourfold fall in RPR titre at 6-12 months confirms adequate treatment. Serology may be negative in very early primary syphilis; if clinical suspicion is high, repeat testing in 2-4 weeks or perform T. pallidum PCR on the ulcer swab.

Recommended STI screen by risk group

Additional investigations

Proctoscopy with rectal smear microscopy is indicated for symptomatic proctitis. If C. trachomatis NAAT is positive from a rectal specimen, request LGV genotyping. Gram stain of urethral discharge showing intracellular Gram-negative diplococci is highly specific for gonorrhoea in symptomatic males. Absence of organisms on Gram stain with a discharge indicates non-gonococcal urethritis (NGU), most commonly caused by chlamydia.

5. Management

General principles

Treat empirically when clinical suspicion is high rather than waiting for results, particularly in symptomatic patients or following a high-risk exposure. Always treat both gonorrhoea and chlamydia concurrently when either is suspected, given frequent co-infection. Arrange partner notification for all confirmed STIs. Advise abstinence or condom use until the patient and partner(s) have completed treatment.

The regimens below follow the Australian STI Management Guidelines (ASHM) and Therapeutic Guidelines: Antibiotic, which together provide the current standard of care.

Chlamydia

Uncomplicated urogenital or rectal chlamydia is treated with doxycycline 100 mg orally twice daily for 7 days as first-line therapy. A single 1 g oral dose of azithromycin is an alternative when adherence to a 7-day course is a concern, though doxycycline achieves superior cure rates for rectal infection. Doxycycline is contraindicated in pregnancy; azithromycin 1 g orally as a single dose is used instead. Epididymo-orchitis attributable to an STI requires a 14-day course of doxycycline alongside treatment for gonorrhoea.

Gonorrhoea

Ceftriaxone 500 mg IM as a single dose is the standard first-line treatment in Australia. When chlamydia has not been excluded, add azithromycin 1 g orally at the same visit. Susceptibility testing guides therapy when resistance is identified. Ciprofloxacin should only be used if susceptibility is confirmed beforehand, given widespread quinolone resistance. Disseminated gonococcal infection requires intravenous or intramuscular ceftriaxone 1 g once daily for 7 days, with transition to oral therapy after 48 hours of clinical improvement. Meningitis requires 14 days of treatment and endocarditis requires 28 days. Gonococcal conjunctivitis in adults is highly contagious and requires barrier precautions, saline irrigation, and parenteral ceftriaxone.

Syphilis

Early syphilis (primary, secondary, and early latent) is treated with a single intramuscular dose of benzathine penicillin G 1.8 g. Late latent or syphilis of unknown duration requires three weekly doses. Neurosyphilis requires high-dose intravenous benzylpenicillin for 10-14 days. Doxycycline is an alternative for penicillin-allergic patients in non-pregnant adults (100 mg orally twice daily for 14 days for early syphilis, 28 days for late latent). Pregnant patients with penicillin allergy require specialist input and possible desensitisation, as penicillin is the only agent proven to prevent congenital syphilis. The Jarisch-Herxheimer reaction (fever, rigors, and headache within hours of treatment) is common in early syphilis and managed with paracetamol and reassurance.

Non-gonococcal urethritis (NGU)

First-line treatment is doxycycline 100 mg orally twice daily for 7 days. An alternative is azithromycin 500 mg stat followed by 250 mg daily for 4 days. Persistent or recurrent NGU warrants consideration of Mycoplasma genitalium (test by NAAT if available) and addition of metronidazole for possible Trichomonas vaginalis.

Disposition

Uncomplicated STIs are managed in the outpatient setting. Refer to sexual health or genitourinary medicine for complex cases, treatment failures, penicillin allergy in pregnancy, LGV, neurosyphilis, and disseminated infection. Involve a senior clinician or specialist early for any pregnant patient with syphilis.

6. Australian-specific considerations

Syphilis outbreak in Aboriginal and Torres Strait Islander communities

Australia has experienced an ongoing outbreak of infectious syphilis in Aboriginal and Torres Strait Islander people, particularly across remote Northern Territory, Queensland, Western Australia, and South Australia. Congenital syphilis cases have occurred as a direct consequence. Any Aboriginal or Torres Strait Islander person of reproductive age presenting to a health service in an affected region should be offered syphilis serology as a routine part of their care, regardless of the presenting complaint. Antenatal syphilis screening is mandatory and should occur at the first antenatal visit, at 28 weeks, and again at delivery in high-prevalence areas. Cultural safety, use of Aboriginal health workers, and community-based testing are central to outbreak control.

Rural and remote considerations

Access to intramuscular benzathine penicillin may be limited in remote settings. Telehealth consultation with a sexual health physician or infectious diseases specialist supports appropriate management. Retrieval or transfer should be arranged for disseminated infection, neurosyphilis, or complicated PID requiring intravenous therapy. Point-of-care syphilis testing (rapid treponemal tests) is available and validated for use in remote primary care settings.

PBS and MBS

Doxycycline, azithromycin, and ceftriaxone are PBS-listed. Benzathine penicillin G is available through hospital pharmacies and some community pharmacies. The MBS item 715 (Aboriginal and Torres Strait Islander health assessment) provides an opportunity for opportunistic STI screening. Contact tracing is a public health obligation; notification of gonorrhoea, syphilis, and chlamydia (in some jurisdictions) to the relevant state or territory health authority is mandatory.

Mandatory notification

Chlamydia, gonorrhoea, and syphilis are all notifiable conditions in every Australian state and territory. Notification is the responsibility of the diagnosing clinician or laboratory. Congenital syphilis is separately notifiable.

Clinical pearls

• A painless, indurated, solitary genital ulcer is syphilis until proven otherwise. Serology may be negative in the first weeks of primary infection, so swab the ulcer for T. pallidum PCR and repeat serology at 4 weeks if initial results are negative.
• Gonorrhoea and chlamydia co-infection is common. Treat both empirically at the same visit rather than waiting for individual results, particularly in symptomatic patients.
• Rectal chlamydia requires doxycycline for 7 days rather than a single-dose azithromycin regimen, as cure rates for rectal LGV and non-LGV rectal infection are substantially higher with the longer course.
• Any GBMSM with symptoms resembling inflammatory bowel disease should have LGV considered and rectal C. trachomatis NAAT with genotyping requested, as LGV proctitis closely mimics IBD clinically.
• In Australia, syphilis in a person of reproductive age from a remote or regional area should prompt urgent partner notification and antenatal screening if pregnancy is possible, given the active congenital syphilis outbreak.
• The Jarisch-Herxheimer reaction after penicillin treatment for syphilis is not an allergic reaction. Reassure the patient, give paracetamol, and do not withhold or change the antibiotic.

Sources

• AIHW Aboriginal and Torres Strait Islander health reports
• MBS Online (Medicare Benefits Schedule)
• PBS Schedule (Pharmaceutical Benefits Scheme)
• Therapeutic Guidelines (eTG)