What is an STI? An STI is an infection or disease that is transmitted through sexual contact Common STI’s include: Chlamydia Genital Herpes Genital Warts Gonorrhoea Hepatitis HIV/AIDS Syphilis Trends of STI’s in Australia Chlamydia is one of the most common Sexually Transmitted Infections in Australia HIV is also quite common in Australia Hepatitis B is also frequent, but is most commonly transmitted through blood.