What is HIV?HIV stands for Human Immunode ciency Virus. HIV destroys certain blood cells called CD4 or T cells. These cells are crucial to the normal function of the immune system which defends the body against illness. When the immune system has been compromised by HIV, a person typically develops a variety of cancers and viral, bacterial, parasitic, and fungal infections. What is AIDS?AIDS stands for Acquired Immunode ciency Syndrome. It occurs when the immune system is weakened by HIV to the point where a person develops any number of diseases or cancers. A person without these diseases or cancers can still be diagnosed with AIDS if a laboratory test shows a severely damaged immune system. How is HIV detected?It is impossible to look at someone and know whether he or she is HIV-positive. The only sure way to determine this is through an HIV test. A blood sample can reveal the presence of the virus. If the blood sample contains HIV antibodies—proteins the body produces to ght o the infection—the person is HIV-positive. How is HIV transmitted?HIV is primarily transmitted through unprotected sex, including vaginal, anal and oral sex. Certain bodily uids including blood, semen, vaginal secretions and breast milk spread HIV. The virus can also be transmitted through contaminated needles, which can happen when infected drug users share needles. An HIV-infected woman can pass the virus to her baby during pregnancy or breast-feeding. HIV is also transmitted through contaminated, unscreened blood supplies.