Contamination

Micro-organisms can be transported through the environment in a number of ways; they can be conveyed in liquids or in aerosols, on particles of solids, or either inside objects or on their surfaces. An object or environment can become contaminated either by direct contact with a carrier of contamination or by contact with some intermediary that has itself has come into direct contact with a source of micro-organisms (Figure 1). Almost anything can qualify as an intermediary according to the definition given above. For example, as Figure 2 shows a person may sneeze into her hand and then transfer viral particles from her hand to a door handle which, as a result, becomes a source of infection. To give another example, a healthcare worker treating a patient infected with antibiotic resistant bacteria may transmit the infection to another patient simply by hand contact. As used here, the term contamination will be taken as referring to the unwanted transfer of infectious biological agents from one location to another. Moreover, the term ‘infectious biological agent’ is meant to include both prokaryotic and eukaryotic micro-organisms, viruses and prions. [continues...]