If HIV isn't treated  the gradual weakening of the immune system it causes leaves the body vulnerable to serious infections and cancers which it would normally be able to fight off. These are called ‘opportunistic infections' because they take the opportunity of the body’s weakened immunity to take hold.

If you develop certain opportunistic infections, you are diagnosed as having AIDS. AIDS stands for Acquired Immune Deficiency Syndrome. Different people diagnosed as having AIDS may become unwell with different illnesses, depending on the specific opportunistic infections they develop. This is why AIDS is not considered a disease, but a syndrome – a collection of different signs and symptoms, all caused by the same virus, HIV.