AIDS can also be fatal. AIDS is mainly caused by the HIV virus that attacks the human immune system, mainly targeting the most important CD4+ T lymphocytes in the human immune system, causing the loss of immune function and making the human body susceptible to bacterial, viral, fungal, parasitic and other infections. Due to the immune deficiency, AIDS can also make a person more susceptible to malignant tumors, which can lead to the death of the patient. Common complications of AIDS include streptococcus, streptococcus pneumoniae and Haemophilus influenzae, which cause bacterial pneumonia, tuberculosis, pneumocystis pneumonia, and various protozoal infections and cytomegalovirus infections, all of which can be life-threatening in severe cases.