text: Sometimes the terms STI and STD are used interchangeably. This can be confusing and not always accurate, so it helps first to understand the difference between infection and disease. Infection simply means that a germ – virus, bacteria, or parasite – that can cause disease or sickness is present inside a person’s body. An infected person does not necessarily have any symptoms or signs that the virus or bacteria is actually hurting their body (they do not necessarily feel sick). A disease means that the infection is actually causing the infected person to feel sick, or to notice something is wrong. For this reason, the term STI – which refers to infection with any germ that can cause an STD, even if the infected person has no symptoms – is a much broader term than STD. \n\nThe term STD refers only to infections that are causing symptoms or problems. Because most of the time, people don’t know they are infected with an STI until they start showing symptoms of disease, the AIDS Resource Center uses the term STD, even though the term STI is also appropriate in many cases.\n\nDepending on the STI, a person may or may not still be able to spread the infection if no signs of disease are present. For example, a person is much more likely to spread herpes infection when blisters are present (STD) than when they are absent (STI). However, a person can spread HIV infection (STI) at any time, even if they haven’t developed symptoms of AIDS (STD).