Methods of preventing infection depend upon the source and route of transmission.

Eradication of reservoir. In a few diseases, for which man is the only natural reservoir of infection, it may be possible to eliminate disease by an intensive programme of case finding, treatment and immunization. This has been achieved in the case of smallpox. If there is an animal or environmental reservoir complete eradication is unlikely, but local control methods may decrease the risk of human infection (for example killing of rodents to control plague, leptospirosis, and other diseases).
For arthropod-vector-borne infections:

destroying vector species (which may be practical in certain circumstances)

taking measures to avoid being bitten (e.g. insect repellent sprays, bed nets).

For food-borne infections. Improvements in food handling and preparation result in less contamination during processing, transport or preparation. Organisms intrinsically present in food can be killed by appropriate preparation and cooking. Improved surveillance and regulation of the food industry, as well as better health education for the public is necessary.

For faeco-oral infections. Thirty per cent of the world's population do not have access to adequate safe drinking water, and over half do not have adequate sanitation. Improvements in water supply could dramatically decrease the prevalence of faeco-oral infections.
For blood-borne infections. Prevention of blood transfer, e.g. in blood transfusions and contaminated medical equipment. Donated blood is routinely tested for infection in most developed countries.

For infections spread by airborne and direct contact. Some airborne-transmitted respiratory infections, and some infections spread by direct contact, can be controlled by isolating patients. This is often difficult, but isolation is useful in patients with severe immunodeficiency to protect them from infection.
Immunization

Cases of some infectious diseases should be notified to the public health authorities so that they are aware of cases and outbreaks.