High prevalence of syphilis in Australia: test, treat and trace

SUMMARY

Syphilis has re-emerged as a significant public health issue in Australia, with rapidly rising case numbers of infectious syphilis and a resurgence of congenital syphilis.

Syphilis may be asymptomatic or present with various clinical manifestations in anogenital, oral or other parts of the body. Untreated syphilis can lead to serious health complications and clinical vigilance is paramount for early diagnosis and treatment.

Syphilis testing is recommended as part of sexual health check-ups and antenatal screening, and for people at increased risk of syphilis or from high-prevalence groups. As the incidence of syphilis is increasing in the general population, clinicians should maintain a low threshold for testing.

Parenteral penicillin is the recommended treatment for all stages of syphilis.

Syphilis is a notifiable condition and is reported by testing laboratories to local public health units. Contact tracing and treatment are essential to prevent re-infection and further transmission.

 

Introduction

Syphilis is a highly infectious, sexually and congenitally transmitted infection caused by the bacterium Treponema pallidum (T. pallidum) and is easily treated when detected early. Untreated syphilis perpetuates transmission and can result in serious complications including cardiovascular and neurological disease, permanent disability and death. Congenital syphilis, resulting from vertical transmission during pregnancy, is associated with adverse pregnancy outcomes, including miscarriage, stillbirth, neonatal death, preterm birth, low birth weight and long-term disability.¹

Increasing prevalence

Australia has experienced a resurgence of syphilis over the last 15 years, disproportionately affecting men who have sex with men in urban areas and heterosexual Aboriginal and Torres Strait Islander people in Northern Australia.² Notification rates across Australia have risen significantly,³ increasing from 8.8 to 24.4 per 100,000 people between 2014 and 2023.⁴ Lack of awareness (among patients and clinicians), socioeconomic disparities, stigma and limited access to culturally appropriate health care are contributing to the rise.⁵

In 2024, there were 5909 cases of syphilis reported in Australia. Of the cases where Indigenous status and sex were reported (n=5375), most were among non-Indigenous men (69%).² Notification rates increased by 13% in non-Indigenous women aged 25 to 34 years, by 40% in Aboriginal and Torres Strait Islander men aged 35 to 44 years and by 50% in Aboriginal and Torres Strait Islander women aged over 45 years.²

Increasing numbers of infectious syphilis cases are evident across all jurisdictions, in urban as well as rural and remote regions; however, Aboriginal and Torres Strait Islander peoples continue to be disproportionately affected, with notification rates 7 times that of non-Indigenous people.² Nationally, the highest notification rates were observed in Aboriginal and Torres Strait Islander people aged 15 to 34 years residing in remote and very remote areas.²

From 2016 to 2024, 99 cases of congenital syphilis and 33 congenital syphilis-associated deaths were reported. This included 20 cases and 10 associated deaths in 2023 alone – the highest annual number since 1995.² Eleven cases of congenital syphilis resulting in 4 infant deaths were reported in the first 9 months of 2025.²

Effective syphilis control requires increasing public awareness, preventive strategies, screening, timely diagnosis and appropriate treatment, as well as contact tracing that is coordinated with broader public health responses.⁵

Australian response

A coordinated national response to the widespread and sustained increase in syphilis cases in Australia is detailed in the National Syphilis Response Plan 2023 to 2030.⁶

The overarching goals are:

1. Strengthen prevention and testing strategies for syphilis in priority populations and settings, targeting high-burden areas.
2. Reduce ongoing transmission and incidence of syphilis across priority populations.
3. Reduce morbidity and mortality associated with syphilis.
4. Eliminate congenital syphilis (defined as sustained zero congenital syphilis cases).⁶

Australia’s commitment to tackle syphilis was further reinforced by the declaration of syphilis as a Communicable Disease Incident of National Significance by Australia’s Chief Medical Officer in August 2025.⁷

 

Transmission of syphilis

Syphilis is transmitted through direct sexual contact or vertically from mother to child via transplacental passage of T. pallidum during pregnancy. Untreated syphilis is infectious to sexual partners in the primary, secondary and early latent stages (Table 1). Untreated late latent disease is not infectious to sexual partners.⁸ The likelihood of vertical transmission in pregnancy depends on the stage of maternal infection and is much higher in untreated mothers with primary or secondary syphilis during the third trimester (60 to 100%), compared with untreated mothers with early latent disease (40%) or late latent disease (less than 8%).⁹

Table 1 Clinical features of syphilis by stage of infection

Stage of infection	Clinical features
Primary (9 to 90 days after infection)	Syphilitic ulcer (chancre): starts as a papule or nodule that ulcerates at the site of inoculation can be solitary or multiple; may be painful or painless indurated with a clean base discharging clear serum mainly anogenital; however, extragenital (mainly oral) sites may also be involved Regional, localised painless lymphadenopathy
Secondary (appears concurrently with primary lesions or 6 to 8 weeks after syphilitic ulcer)	Rash: generalised maculopapular (50 to 70%), papular (12%), macular (10%) or ulceronodular; does not usually itch rash involving palms and soles (11 to 70%) Mucocutaneous lesions (oral, genital, anal), condylomata lata (wart-like growths) Patchy alopecia (4 to 11%) Fever, headache, sore throat Generalised painless lymphadenopathy Hepatitis Glomerulonephritis Ophthalmic syphilis – anterior uveitis, optic neuropathy, interstitial keratitis, retinitis Otosyphilis – sensorineural hearing loss, tinnitus, vertigo Neurological involvement – meningitis, cranial nerve palsies
Early latent (less than 2 years after exposure)	No symptoms 25% recurrence of secondary stage symptoms
Late latent (more than 2 years after exposure)	No symptoms
Tertiary (1 to 46 years after exposure)	Neurosyphilis – meningovascular or parenchymatous; general paresis (progressive illness with dementia, seizures and hemiparesis) and tabes dorsalis (sensory ataxia, lightning pains, pupillary abnormalities, dorsal column loss with absent reflexes, impaired joint position and vibration sense) Cardiovascular syphilis – aortitis, aortic regurgitation, coronary ostial stenosis, aortic aneurysm, angina, heart failure Gummatous syphilis – necrotic, destructive granulomatous lesions

 

Clinical manifestations of syphilis

Syphilis has long been known as ‘the great imitator’ because of its wide range of signs and symptoms. Following a 9- to 90-day incubation period (mean 21 days), the clinical features follow a characteristic pattern throughout the disease’s natural history (Table 1). However, approximately 50% of syphilis infections are asymptomatic.¹⁰

Main clinical manifestations of primary syphilis are genital, anal or oral ulcers (chancres). These may go unnoticed, as they can be painless, or may appear in areas that are not easily noticed.

If manifestations of primary syphilis are not recognised or treated, they can resolve without treatment. However, patients may present several weeks later with multiple nonspecific manifestations of secondary syphilis, including generalised or localised skin rashes (that may involve the palms and soles), generalised painless lymphadenopathy, hair loss, mucocutaneous lesions and constitutional symptoms. Some may present with visual, auditory and/or neurological symptoms and signs (Table 1).

Untreated syphilis becomes asymptomatic after about 2 years, leading to a period of latent syphilis. Latent disease is asymptomatic although 25% in the early latent stage develop recurrence of secondary symptoms.⁸ Tertiary syphilitic manifestations may occur years after an untreated infection (Table 1).

 

Testing recommendations

Syphilis testing should be routinely performed in:

• anyone with signs and symptoms of syphilis
• all people attending sexually transmissible infection (STI) check-ups^11,12
• all pregnant people at the first antenatal visit or first-trimester tests, with repeat screening recommended at 26 to 28 weeks and again at either 36 weeks or birth (whichever comes first), regardless of risk¹³
• pregnant people at increased risk of syphilis, for whom testing is recommended at 5 time points: the first antenatal visit, 26 to 28 weeks, 36 weeks, at birth, and 6 weeks postpartum¹³
• priority populations, representing those at increased risk of infection or adverse outcomes from syphilis, or those from high-prevalence groups.⁶ These include: Aboriginal and Torres Strait Islander people; gay, bisexual and other men who have sex with men; people who can become pregnant; and people experiencing socioeconomic disadvantage or barriers to health care access¹⁴
• people being assessed for human immunodeficiency virus (HIV) pre- or post-exposure prophylaxis (PrEP or PEP).¹⁴

The incidence of syphilis is also increasing in the general population, so clinicians should have a low threshold for testing in the broader community.

 

Diagnosis of syphilis

Diagnosis of syphilis requires a combination of history, clinical assessment and investigations.

Direct detection

Traditionally, direct detection of syphilis was based on dark ground microscopy; however, this has been replaced by nucleic acid amplification testing (NAAT) to detect T. pallidum DNA from dry swabs, scrapings, biopsies of any lesions of concern and cerebrospinal fluid or placental tissue samples.¹⁵ If suspicious lesions are present, clinicians should swab the lesion using a dry PCR swab.

Serological tests

Clinicians should request syphilis serology when ordering investigations for syphilis. Laboratories will perform treponemal-specific antibody tests, followed by non-treponemal tests in those with positive treponemal antibody tests (Figure 1).

Treponemal tests

Treponemal tests detect treponemal-specific antibodies and can be used to determine if a person has ever been exposed to or infected with T. pallidum. Results are usually reported as reactive or non-reactive. If a person is infected with syphilis, treponemal tests are usually reactive within 3 months of exposure.

Serology samples are first screened using assays, such as treponemal enzyme immunoassay (EIA) or chemiluminescent immunoassay (CMIA), which detect IgM and IgG antibodies specific to T. pallidum. Reactive screening tests are then confirmed by reflex treponemal-specific tests, such as T. pallidum haemagglutination assay (TPHA) or T. pallidum particle agglutination (TPPA) assay, performed by the laboratory.

Non-treponemal tests

Quantitative, non-treponemal tests, such as the rapid plasma reagin (RPR) and Venereal Diseases Research Laboratory (VDRL) tests, are performed when treponemal-specific tests are reactive. These tests detect antibodies that are reactive to lipoidal antigens shared by both the host and T. pallidum.

Non-treponemal tests are useful for assessing a patient’s response to treatment and for identifying re-infection in people with a history of syphilis. A 4-fold titre decrease in the non-treponemal test (RPR or VDRL) compared with the treatment-day titre (e.g. 1:64 to 1:8) indicates an adequate treatment response, whereas a 4-fold increase (1:4 to 1:32) indicates re-infection.

It is important to seek advice from a sexual health or infectious diseases specialist if a 4-fold decrease in non-treponemal titre does not occur 12 months after treatment.

False negative serology results

False negative syphilis serology can occur within the first 3 months of infection in an asymptomatic person and for up to 2 weeks during the primary syphilis stage (after the syphilitic ulcer develops). In addition, false negative non-treponemal (VDRL or RPR) results may occur in secondary or early latent syphilis due to very high antibody titres (called the ‘prozone phenomenon’).

Rarely, a positive CMIA or EIA with a negative TPPA or TPHA and a negative RPR may represent a false positive result or very early infection. Testing should be repeated in 1 to 2 weeks if there is suspicion of new infection.

All states and territories provide telephone support for clinicians through syphilis registers, sexual health clinics or dedicated helplines to assist with interpreting test results based on patients’ previous testing and treatment.

Rapid point-of-care tests

Point-of-care tests can facilitate early diagnosis and treatment in people without a prior history of syphilis.¹⁵ Point-of-care tests have been used in some Australian primary healthcare settings, including some government and Aboriginal Community Controlled Health Services, for several years in combination with conventional syphilis serology.¹⁶ Whole-blood samples obtained via finger prick or venepuncture can be used. A limitation of these tests is that they cannot differentiate new infections from previous syphilis infections.

Determine Syphilis TP (a treponemal-specific immunochromatographic test) is the only syphilis point-of-care tests currently registered by the Therapeutic Goods Administration in Australia. It has demonstrated an overall sensitivity of 97.3% and specificity of 96.4%.¹⁷

 

Treatment of syphilis

Penicillin administered parenterally is the preferred treatment for all stages of syphilis (Table 2).

Table 2 Recommended penicillin doses for syphilis by stage of infection¹²

Stage of syphilis	Treatment
Early (primary, secondary or early latent [less than 2 years after exposure])	Benzathine benzylpenicillin 2.4 million units (1.8 g) via intramuscular injection, given as a stat dose
Late (more than 2 years after exposure) or syphilis of unknown duration	Benzathine benzylpenicillin 2.4 million units (1.8 g) via intramuscular injection, given weekly for 3 weeks
Neurosyphilis	Aqueous crystalline penicillin 4 million units via intravenous injection every 4 hours for 14 days

For treatment to be effective, treponemicidal concentrations of the antibiotic must be achieved in serum and cerebrospinal fluid. Antibiotic concentrations should remain treponemicidal for at least 7 days to cover several treponemal division cycles, each of which is 30 to 33 hours in early syphilis. More slowly dividing treponemes in late syphilis warrant a longer duration of treatment.⁸

Patients should be informed they may develop a self-limiting acute illness, known as the Jarisch–Herxheimer reaction, within the first 24 hours of starting treatment for primary and secondary syphilis. It is considered to be a response to antigens released from dead treponemes. The Jarisch–Herxheimer reaction may present with varying severity, including fever, headache, myalgia, joint pains, chills and rigors lasting for several hours. Supportive treatment with antipyretics and fluids is recommended.

There have been recent shortages of benzathine benzylpenicillin in Australia. Clinicians should stay informed of local shortages and advice about managing these shortages, including alternatives to the usually available brands.¹⁸

If a patient is allergic to penicillin, or if benzathine benzylpenicillin is unavailable, oral doxycycline can be used in non-pregnant individuals.¹⁹

Treatment in pregnancy

All cases of syphilis in pregnancy should be discussed with a sexual health or infectious disease specialist. Benzathine benzylpenicillin is the only recommended therapy during pregnancy. Desensitisation to penicillin is required for those who report penicillin allergy.¹² Appropriate treatment will lead to a 4-fold reduction in RPR titre; however, this usually takes 3 months to 1 year.

A Jarisch–Herxheimer reaction in the second half of pregnancy may precipitate uterine contractions and preterm labour. Patients should be advised to report symptoms of labour or decreased fetal activity to their healthcare provider immediately.²⁰

Infants of mothers who had been diagnosed or treated for syphilis during pregnancy, or those otherwise deemed at high risk of congenital syphilis, should be managed as per jurisdictional guidelines.

 

Notification and contact tracing

Syphilis is a notifiable condition in all Australian states and territories and cases are reported to the local public health unit by the testing laboratories.

It is important for clinicians to notify positive point-of-care tests to public health units.

Anyone exposed through sexual contact to a person who has syphilis should be evaluated clinically and undergo serological testing (Table 3).

Table 3 Contact tracing based on the clinical stage of syphilis²¹

Stage of syphilis	Trace-back period
Primary	3 months plus duration of symptoms OR Last negative test
Secondary	6 months plus duration of symptoms OR Last negative test
Early latent	12 months OR Last negative test
Late latent or tertiary	Test current partner(s)

Presumptive treatment with benzathine benzylpenicillin 2.4 million units (1.8 g) intramuscularly as a stat dose is recommended for all sexual partners within the previous 3 months of primary or secondary infection regardless of their syphilis serology.¹²

It is critical to test and treat all partners of a pregnant person diagnosed with syphilis to minimise the risk of re-infection.

Primary care clinicians may assist patients with contact tracing directly or refer them to public health units or sexual health services for assistance. Resources such as Let Them Know or The Drama Downunder can assist patients with anonymous notification. Better to Know is a sexual health resource for Aboriginal and Torres Strait Islander peoples that provides culturally appropriate STI and bloodborne virus health promotion materials and an anonymous notification tool.

 

Follow-up

Follow-up of patients is essential to confirm successful treatment, ensure contact tracing and provide opportunity for further education.

It is recommended to review patients clinically and repeat non-treponemal testing at 3, 6 and 12 months after completing treatment. Ten to twenty percent of people with primary or secondary syphilis who are appropriately treated will not achieve the 4-fold decrease in non-treponemal titre within 12 months after treatment.²² These patients should be discussed with a sexual health specialist.

 

Prevention

Prevention of syphilis remains a cornerstone of Australia’s response to the syphilis crisis.⁶ Strengthening systems for effective person-centred care in a culturally appropriate and gender-inclusive manner is an essential strategy. Focusing on health promotion messaging, support for safe sexual practices and regular sexual health screening are essential pillars for success.

Pharmacological prevention with a single oral dose of doxycycline 200 mg within 72 hours after condomless sex (doxycycline post-exposure prophylaxis, Doxy-PEP) has been demonstrated to reduce the risk of syphilis by 70 to 80% in gay and bisexual men who have sex with men.²³ It is important to discuss Doxy-PEP with gay and bisexual men and trans women who are at increased risk of syphilis.²⁴

 

Support for clinicians

The Australian STI Management Guidelines, ASHM Decision Making In Syphilis tool and Therapeutic Guidelines provide national standards for testing and treatment. If required, clinicians can seek support from state or territory sexual health clinics when treating patients with syphilis. Northern Territory, Queensland, South Australia and Western Australia have syphilis registers that can help clinicians find previous syphilis testing results and treatment history in people living in those jurisdictions.

 

Conclusion

Syphilis has re-emerged as a major public health problem in Australia and globally. Ensuring equitable and ongoing access to prevention, regular and opportunistic testing, timely treatment and an effective public health response for key populations is essential for syphilis control.

This article was finalised on 4 June 2026.

Conflicts of interest: The authors declared no conflicts of interest.

This article is peer reviewed.

 

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