Infectious diseases also called communicable diseases kill more people worldwide than any other single cause. Infectious diseases are caused by germs. These germs are tiny living things that are found everywhere - in air, soil and water. You can get an infection by touching, eating, drinking or breathing something that contains a germ. Germs can also spread through animal and insect bites, kissing and sexual contact. Vaccines, proper hand washing and medicines can help prevent infections.