"HIV" stands for Human Immunodeficiency Virus. If a person gets infected, the immune system can't get rid of the virus. That means once you get infected, you have it for life.
HIV manages to hide for a long period of time and attacks CD4 cells of your immune system. Over time, HIV can destroy so many of your CD4 cells that your body can't fight any more infections and diseases.
Although the cure for HIV infection is not yet available, the treatment can keep the virus under control and allow the immune system to restore its function. People on HIV treatment can live a healthy and productive life.
AIDS (Acquired Immunodeficiency Syndrome) is caused by HIV. Without treatment, about half of HIV infected people will progress to AIDS within 10 years. On the contrary, HIV treatment prevent AIDS and significantly prolongs life expectancy. Not everyone who has HIV experiences this stage.
Once progress to this stage, the immune system is seriously damaged. The infected person is more vulnerable to certain cancers and a wide range of infections. These types of infections are known as opportunistic infections (OIs) because they take advantage of a person's weakened immune system and normally do not attack healthy people. In Hong Kong, you are considered to have progressed to AIDS if you have one or more specific OIs such as Pneumocystis pneumonia (PCP), tuberculosis (TB) and fungal infections or certain cancers. HIV treatment is the only way to delay the progression to AIDS.
Most infected people do not have any symptoms at all for years and continue to look normal and healthy. Even if they have, the symptoms can vary depending on the individual and the stage of the disease.