The biohazard symbol should be prominently displayed on laboratory doors and any equipment (refrigerators, incubators, centrifuges) that contain infectious material. The air-handling system of a microbiology laboratory should move air from lower to higher risk areas, never the reverse. Ideally, the microbiology laboratory should be under negative pressure, and air should not be recirculated after passing through microbiology (see Chapter 62 for a more detailed discussion of negative pressure in microbiology laboratories). The selected use of BSCs for procedures that generate infectious aerosols is critical to laboratory safety. Many infectious diseases, sucih as plague, tularemia, brucellosis, tuberculosis, and legionellosis, may be contracted by inhaling infectious particles, often present in a droplet of liquid. Because blood is a primary specimen that may contain infectious virus particles, subculturing blood cultures by puncturing the septum with a needle should be performed behind a barrier to protect the worker from droplets. Several other common procedures used to process
Aerosol control in a class 1 cabinet
specimens for culture, notably mincing, grinding, vortexing, and preparing direct smears for microscopic examination, are known to produce aerosol droplets. These procedures must be performed in a BSC.
The microbiology laboratory poses many hazards to unsuspecting and untrained people; therefore, access should be limited to employees and other necessary personnel (biomedical engineers, housekeepers). Visitors, especially young children, should be discouraged. Certain areas of high risk, such as the mycobacteriology and virology laboratories, should be closed to visitors. Custodial personnel should be trained to discriminate among the waste containers, dealing only with those that contain noninfectious material. Care should be taken to prevent insects from infesting any laboratory area. Mites, for example, can crawl over the surface of media, carrying microorganisms from colonies on a plate to other areas. Houseplants can also serve as a source of insects and should be carefully observed for infestation, if they are not excluded altogether from the laboratory environment. A pest control program should be in place to control rodents and insects.
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