Infections that occur during the hospital stay, not present at the time of hospitalization, but become clinically apparent during hospitalization or after discharge from the hospital. As a general rule new infection occurring after 48 hrs of hospitalization can be considered as nosocomial. Mostly nosocomial infections are caused by Bacteria but Viruses, Chlamydia, Fungi and Protozoa can also cause such infections. Mostly nosocomial infections occur in Teaching hospitals.