Infectious disease is a medical specialty dealing with the diagnosis, control and treatment of infections. An infectious disease specialist's practice may consist largely of managing nosocomial infections or it may be out-patient based. Infectious disease specialists typically serve as consultants to other physicians in cases of complex infections and often manage patients with HIV/AIDS and other forms of Immunodeficiency. Although many common infections are treated by physicians without formal expertise in infectious diseases, specialists may be consulted for cases where an infection is difficult to diagnose or manage.