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Chapter 10 : Biosafety for Microorganisms Transmitted Primarily by the Airborne Route
This chapter focuses on certain organisms for which the airborne route is the predominant means of transmission to humans. The in vivo tissue forms of the fungi are yeasts or spherules and are not readily transmissible to other humans, either by direct contact or by the airborne route. Efficient means of production of droplet nuclei in nature are sneezing, coughing, and vibration of the larynx, all of which introduce energy that subdivides fluids into tiny droplets. Qualitative risk assessment is encompassed in the biosafety levels (BSLs) established in Biosafety in Microbiological and Biomedical Laboratories. The current laboratory safety-oriented biosafety classification of microorganisms reflects what is known regarding the tendency for an organism to be transmitted by an airborne route, if there is effective treatment available for infection, and whether a vaccine is available. Mycobacterium tuberculosis must be inhaled deep into the lung and reach the alveoli as the first step in a successful infection of a new host. Hazard assessment in the laboratory should focus critical attention on the manipulation of fluids. All opening of tubes, pipetting, transfers, sonication, vortex mixing, etc., should be carefully contained. Many bacteria that have caused laboratory acquired infections in humans include Brucella, Francisella tularensis, and Burkholderia pseudomallei. The greatest problem encountered in the laboratory safety arena is generally not those involving decision patterns for known problems. Rather, it is more often the unknown safety precautions required for a particular agent that causes the laboratorian to fear infection.