Microorganisms are easily transmitted from place to place via vectors such as insects or animals, by humans that can harbor the infectious organism and shed them to the environment, and via movement through the air (in the case of some bacteria, yeast, and viruses). Microorganisms can adapt to antimicrobial treatments (the best example being the acquisition of inheritable antibiotic resistance by bacteria). Thus, the potential for the spread of infection by disease-causing microbes is substantial unless steps are taken to limit the spread. Such strategies are collectively termed infection control.

For many microorganisms, particularly bacteria, contact transmission is a common means of spread of infection. This can involve the fecal-oral route, where hands soiled by exposure to feces are placed in the mouth. Day care workers and the infants under their charge are a significant focus of such Escherichia coli infections. As well, touching a contaminated...