An STI (Sexually Transmitted Infection) is an infection that is transmitted mainly through unprotected sexual intercourse (vaginal, oral, anal), but also through blood or from mother to child. Some infections have no symptoms, but can lead to serious complications if left untreated. The most common are HIV, chlamydia, gonorrhoea, syphilis, herpes, papillomavirus (HPV) and hepatitis B/C. Regular screening and condom use are the best means of prevention.