Sterilize, disinfect, sanitize, fumigate can mean to subject to a process or treatment for the destruction of living organisms, especially microorganisms.
Sterilize suggests drastic methods (as the application of intense heat, boiling, or the use of strong chemicals) with the intent of destroying all microorganisms whether they are disease-producing or not. The term usually suggests means taken to avoid infection.
Disinfect also suggests vigorous methods (as exposure to strong sunlight and fresh air, thorough washing, and the use of special chemicals) with the intent of destroying all infective agents; the term usually suggests an intent to free from germs something that is known or feared to be infected.
Sanitize, which basically means to make sanitary, is often preferred by public health officials when the reference is to preventive measures affecting the health of a community (as the treatment of drinking water or the cleansing of food processing facilities) and when neither sterilize (because it suggests complete destruction of microorganisms and often implies the taking of measures too drastic for general use) nor disinfect (because it suggests the actual presence of disease germs) exactly fits their needs or makes clear their intention.
Fumigate is associated with these terms only because fumigation was once the usual method of disinfection; it implies the use of fumes (as smoke or gas) that are destructive not only of microorganisms but of such pests as cockroaches, beetles, and bedbugs.