Human immunodeficiency virus infection (HIV) is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV). Following initial infection a person may not notice any symptoms or may experience a brief period of influenza-like illness. Typically this is followed by a prolonged period with no symptoms. If the infection progresses it interferes more with the immune system increasing the risk of developing common infections such as tuberculosis as well as other opportunistic infections and tumors which are otherwise rare in people who have normal immune function.