Infectious disease, also known as infectious diseases, infectious medicine, infectious disease medicine or infectiology, is a medical specialty dealing with the diagnosis, control and treatment of infections. An infectious disease (ID) specialist's practice may consist largely of managing nosocomial (hospital-acquired) infections, or it may be out-patient based. Infectious Diseases specialists employ a variety of antimicrobial agents to help treat infections. The type of agent used depends on the organism that is causing the infection. Antibiotics are used to treat bacterial infections; antiviral agents treat viral infections ; and antifungal agents treat fungal infections.