Immunodeficiency (or immune deficiency) is a state in which the immune system's ability to fight infectious disease is compromised or entirely absent. Most cases of immunodeficiency are acquired ("secondary") due to extrinsic factors that affect the patient's immune system. Examples of these extrinsic factors include infections, such as by Human Immunodeficiency virus (HIV), extremes of age and environmental factors, such as nutrition. In the clinical setting, the immuno-suppression quality of some drugs, such as steroids, can be utilised. Examples of such use is in transplant surgery as an anti-rejection measure and in patients suffering from an over-active immune system. Some people are born with defects in their immune system, or primary immunodeficiency. A person who has an immunodeficiency of any kind is said to be immunocompromised. An immunocompromised person may be particularly vulnerable to opportunistic infections, in addition to normal infections that could affect everyone. Immunodeficiency may also decrease cancer immunosurveillance