However, a person can spread HIV infection (STI) at any time, even if he/she has not developed symptoms of AIDS (STD). Thus, one may presume that, if a person is infected with an STI, e.g., chlamydia, gonorrhea, genital herpes, it was transmitted to him/her by means of sexual contact. Not all STIs are symptomatic, and symptoms may not appear immediately after infection. Public health officials originally introduced the term sexually transmitted infection, which clinicians are increasingly using alongside the term sexually transmitted disease in order to distinguish it from the former. In 1996, the World Health Organization estimated that more than 1 million people were being infected daily.

In some instances a disease can be carried with no symptoms, which leaves a greater risk of passing the disease on to others. Prior to the invention of modern medicines, sexually transmitted diseases were generally incurable, and treatment was limited to treating the symptoms of the disease. Specifically, the term STD refers only to infections that are causing symptoms. An infected person does not necessarily have any symptoms or signs that the virus or bacteria is actually hurting his or her body; they do not necessarily feel sick. According to the Ethiopian Aids Resource Center FAQ, “Sometimes the terms STI and STD are used interchangeably.