Sexually Transmitted Infections (STIs)
Common, usually silent and nearly all treatable. Regular testing is the only way to know, and it’s often just a urine test or a swab you can take yourself.
Quick answer: Most STIs, including chlamydia and gonorrhoea, cause no symptoms, so testing is the only way to know. Testing is usually a urine sample, self-collected swab or blood test. Chlamydia, gonorrhoea and syphilis are cured with antibiotics; herpes and HIV are controlled with medicines. Condoms, vaccines and PrEP prevent many infections.
How common. WHO estimates more than 1 million STIs are caught every day worldwide. In 2020 there were about 129 million new chlamydia infections, 82 million gonorrhoea, 7.1 million syphilis and 156 million trichomoniasis.
Testing
- Who: anyone with a new partner or more than one partner, anyone with symptoms, and anyone whose partner has an STI. In Australia, a yearly chlamydia test is recommended for sexually active people under 30, and gay, bisexual and other men who have sex with men at higher risk are advised to test every 3 months.
- How: a urine sample or a self-collected vaginal, throat or anal swab for chlamydia and gonorrhoea, and a blood test for syphilis, HIV and hepatitis B and C. Testing the throat and anus matters, as infections there are often silent.
- Timing: some infections take time to show. Chlamydia and gonorrhoea are usually detectable about 2 weeks after exposure, HIV up to 6 weeks with a combined blood test, and syphilis up to 12 weeks, so you may need a repeat test.
- Where: your GP, a sexual health clinic (free and confidential in many places), or some online and self-testing services. HIV self-test kits are available in Australia.
Nobody can tell by looking. Not you, not them, not even your GP. That’s what the test is for.
The main infections
- Chlamydia: the most common bacterial STI. Most people have no symptoms; others notice discharge, burning when passing urine, or bleeding after sex. Untreated, it can cause pelvic inflammatory disease (PID), ectopic pregnancy, infertility and painful testicles. Usually cured with doxycycline for 7 days (azithromycin in pregnancy). Retest after 3 months, as reinfection is common.
- Gonorrhoea: can cause discharge and burning, but throat and anal infections are usually silent. It’s becoming resistant to antibiotics, so treatment is a ceftriaxone injection, in Australia usually with azithromycin, and a test of cure about 2 weeks later is often recommended.
- Syphilis: a painless sore (chancre) where the infection entered, then weeks later a rash (often on the palms and soles), fever and swollen glands. Without treatment it can go quiet for years, then damage the brain, eyes, nerves and heart. In pregnancy it can cause stillbirth and congenital syphilis. Treated with benzathine benzylpenicillin injections. In Australia, syphilis has risen sharply in the past decade, including among women and in some First Nations communities, and pregnant women are now advised to have several syphilis tests during pregnancy (for example at the first visit, 26 to 28 weeks and 36 weeks, depending on the state).
- Herpes (HSV-1 and HSV-2): most people who carry it don’t know. It can cause painful blisters or ulcers, worst in the first episode. Antivirals (aciclovir, valaciclovir or famciclovir) shorten episodes, and daily suppressive treatment cuts outbreaks and about halves the chance of passing it on. See cold sores.
- HPV: the most common STI; most infections clear within 2 years. Some types cause genital warts; others can cause cervical, anal, throat and penile cancers. The HPV vaccine prevents most of these. In Australia, one dose is given at school at age 12 to 13, with free catch-up to age 25. Cervical screening still matters: see cancer screening.
- HIV: may cause a flu-like illness a few weeks after infection, then often nothing for years. Daily treatment gives a near-normal life expectancy, and people with an undetectable viral load don’t pass HIV on through sex (undetectable = untransmittable, U=U).
- Others: trichomoniasis, Mycoplasma genitalium, hepatitis B (vaccine-preventable) and mpox (vaccine available for people at higher risk).
After a positive result
- Avoid sex for 7 days after treatment for chlamydia or gonorrhoea, and until partners have been treated.
- Tell recent partners so they can test and get treated: this stops reinfection and protects others. Your clinic can help, and anonymous services such as Let Them Know (Australia) send a text or email for you.
- In Australia, some STIs are notifiable to public health units; this is confidential.
Prevention
- Condoms and dams protect against most STIs, though less well against herpes, HPV and syphilis, which spread by skin contact.
- Vaccines: HPV, hepatitis B, and for some people hepatitis A and mpox.
- HIV PrEP: HIV-negative people at risk can take tenofovir-based tablets; taken as prescribed, PrEP lowers the risk of getting HIV from sex by about 99%. PBS-subsidised in Australia.
- HIV PEP: after a possible exposure, a 28-day course started within 72 hours, the sooner the better. Go to a sexual health clinic or emergency department straight away.
- Doxy-PEP: taking a single 200 mg dose of doxycycline within 72 hours after condomless sex. The 2024 Australian consensus statement says it can be considered mainly to prevent syphilis in gay, bisexual and other men who have sex with men at higher risk, such as after a recent syphilis diagnosis. The US CDC (2024) recommends it for gay and bisexual men and trans women who have had a bacterial STI in the past 12 months. It isn’t recommended for other groups yet: it didn’t work in a study of cisgender women, it may drive antibiotic resistance, and it doesn’t prevent HIV.
See your GP or a sexual health clinic if
- You have discharge, burning when passing urine, sores, a rash, lumps or bleeding after sex
- A partner tells you they have an STI
- You’ve had condomless sex with a new partner
- You’re pregnant or planning pregnancy
Get urgent help for sudden, severe testicle pain (possible torsion, which needs surgery within hours), severe lower tummy pain with fever, or a possible HIV exposure in the past 72 hours (for PEP): go to an emergency department or call 000 (Australia) or your local emergency number for severe pain.
Health days. World Sexual Health Day is on 4 September and World AIDS Day on 1 December: see our health days calendar.
Common questions
How soon after sex can I get tested for STIs?
Chlamydia and gonorrhoea tests are usually accurate from about 2 weeks. HIV can take up to 6 weeks and syphilis up to 12 weeks to show, so you may need a repeat test. Test sooner if you have symptoms.
Can you have an STI without symptoms?
Yes. Most people with chlamydia, gonorrhoea in the throat or anus, herpes or HPV have no symptoms. That’s why regular testing matters.
Do STIs go away on their own?
Some HPV infections clear, but chlamydia, gonorrhoea and syphilis can linger for months or years and cause damage. Get tested and treated.
Do I have to tell my partners?
It’s strongly encouraged so they can be tested and treated. Your clinic can help, and anonymous services can text or email partners for you.
Can you get an STI from oral sex?
Yes. Gonorrhoea, syphilis, herpes and HPV can all spread through oral sex. Throat swabs can check for gonorrhoea and chlamydia.
What is doxy-PEP?
Taking 200 mg of doxycycline within 72 hours after condomless sex to lower the chance of syphilis and chlamydia. Current guidelines limit it to gay, bisexual and other men who have sex with men, and trans women, at higher risk.
How effective is PrEP?
Taken as prescribed, PrEP lowers the risk of getting HIV from sex by about 99%. It doesn’t protect against other STIs.
Is HPV an STI?
Yes, the most common one. Most people catch it at some point and clear it. The vaccine and cervical screening prevent most HPV-related cancers.
Evidence and more information
- WHO: Sexually transmitted infections fact sheet
- ASHM: Australian STI Management Guidelines
- Cornelisse et al, MJA 2024: Australian consensus statement on doxy-PEP
- Bachmann et al, CDC MMWR 2024: Guidelines for doxycycline post-exposure prophylaxis
- NSW Health 2022: GP alert, antimicrobial-resistant gonorrhoea
- Safer Care Victoria: Changes to syphilis testing in pregnancy
- healthdirect: Sexually transmitted infections
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