Sexually transmitted infections

A sexually transmitted infection is caused by viruses, bacteria or parasites and shared through sexual activity.

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Medically reviewed by

Dr Glenn Duns

What are sexually transmitted infections?

A sexually transmitted infection (STI) is an infection you get or give during sexual activity. STIs can be caused by viruses (e.g. human immunodeficiency virus, herpes), bacteria (e.g. gonorrhoea, syphilis) or parasites (e.g. pubic lice).

The prevalence of all STIs is not known because the infections aren’t always diagnosed. In 2017, there were more than 84,000 cases of chlamydia, gonorrhea, hepatitis or syphilis among Australian men, accounting for 56% of all cases, and STI rates are higher in men aged in their 20s and 30s than in other age groups. Aboriginal and Torres Strait Islander males have higher rates of chlamydia, gonorrhea, and syphilis than non-Indigenous males. Depending on the STI, rates vary between 1 in 14,000 Australian men (for HIV) to 1 in 250 (for chlamydia). The rates of some STIs (e.g. gonorrhea and syphilis) have tripled in the last 10 years.

Symptoms of STIs

The symptoms of STIs depend on the bacteria, virus or parasite that cause them.

Some STIs don’t have any symptoms, so you may not know you have one and might pass it on to someone else without knowing.

Causes of STIs

STIs are caused by bacteria, viruses or parasites that are transmitted during oral, anal or vaginal sex, or simply by skin to skin contact.

Diagnosis of STIs

To diagnose an STI, your doctor will ask about your sexual history and practices, examine you, and order tests to look for bacteria and viruses.

Treatment of STIs

The treatment for STIs depends on what causes them. Usual treatments include antibiotics, antiviral medications and creams.

Health effects of STIs

Apart from the short-term effects, STIs can cause permanent damage to your reproductive system and affect your ability to have children. Some STIs can have lifelong effects on your health or require you to take medications for the rest of your life.

What to do about STIs

The best way to deal with STIs is to practise safe sex so you avoid infection in the first place.

If you’re sexually active and have new or different partners, you should have a sexual health check every three months. If you’re in a long-term sexual relationship, you should have a sexual health check at least once a year.

If you have symptoms of an STI, see your doctor straight away. You should avoid sexual contact with someone else in case you give the infection to them.

You should also speak to your sexual partner(s) to let them know you might have an STI so they can arrange to see their doctor.
Sexually transmitted infections

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