Microbiological agents as health risks in indoor air.

Ambient air may be contaminated with or carry significant levels of a variety of potentially harmful microorganisms. There are three major sources of such microbes: a) those arising from microbial decomposition of various substrates associated with particular occupations (e.g., "moldy" hay leading to hypersensitivity pneumonitis), b) those associated with certain types of environments (e.g., Legionnaires' bacteria in water supplies), and c) those stemming from infective individuals harboring a particular pathogen (e.g., tuberculosis). This presentation deals primarily with important microorganisms from occupational and environmental sources and clearly differentiates from case to case transmission via droplet nuclei infection. Microorganisms that are uniformly injurious are differentiated from those that are more opportunistic (i.e., those that cause problems only in people with preexisting debilities). Such microorganisms are categorized according to whether they are allergenic, infectious, or capable of inducing toxic or inflammatory reactions when inhaled. Representative examples from each of these categories, which include bacteria, fungi, rickettsia, and amoebae, are discussed. The conditions responsible for the entrance of significant numbers of these microbes into the air, the mechanisms by which they produce injury, and the methods of prevention are also considered. With attention given to some of the basic sources and requirements for such microorganisms to reproduce and enter the ambient air environment, it is a relatively simple matter to prevent the occurrence of health problems.