Occupational and environmental health effects associated with exposure to biological hazards are mediated primarily by two distinct mechanisms. These mechanisms are infection by intact organisms and immunologic reaction to materials from biological sources. This chapter will describe these basic disease processes and their associated patterns of illness. Practical guidance will be offered as to when particular illnesses should be suspected and how they can be confirmed.
Infection versus colonization
Infection results when living microorganisms (viruses, bacteria, fungi, or parasites) establish an active and growing presence within the human host. This situation creates characteristic pictures of illness. Some disease elements are created by the damage caused directly by the invading pathogens. Others result from the host’s response to the organisms. The detection of disease requires knowledge of the microbiology of the attacking microorganism and an understanding of the human body’s reactions.
Although bacteria are the most commonly isolated source of infectious illness, only some interactions between mammalian organisms and bacteria produce disease. Infection, an event with important medical consequences, must be distinguished from colonization, a term used for the harmless or adventitious presence of the microorganism in contact with human tissue. ...