Biosafety level: A specific combination of work practices, safety equipment, and facilities which are designed to minimize the exposure of workers and the environment to infectious agents.

The biosafety levels are:

• Level 1 -- This level applies to agents that do not ordinarily cause human disease.
• Level 2 -- This level is appropriate for agents that can cause human disease, but whose potential for transmission is limited.
• Level 3 -- This level applies to agents that may be transmitted by the respiratory route which can cause serious infection.
• Level 4 -- This level is used for the diagnosis of exotic agents that pose a high risk of life-threatening disease, which may be transmitted by the aerosol route and for which there is no vaccine or therapy.