While there is a HIGH risk of being infected through unprotected sex with an HIV-positive person, such contact does not always lead to HIV transmission.
The risk increases greatly for the partner who is penetrated (women rather than men, in the case of vaginal sex);
- in the presence of other sexually transmitted infections (STI) such as gonorrhoea, herpes and syphilis; and
- when the HIV-positive person is in the very early and very late stages of HIV infection.
Anal intercourse without condoms carries the highest risk of any sexual activity. Precautions, such as using condoms, should be taken with ALL partners unless it is certain both partners are HIV-negative and are completely faithful to each other.
The risk of catching HIV from sharing contaminated needles or syringes is extremely high (around 80%), while the chance of a pregnant mother infecting her baby is between 15 to 30%.
-- Source: Action for AIDS Singapore