The actual source of exposure can be defined for only 20 percent
of the reported cases.
The most common known sources of exposure consist of direct
inoculation by needle and syringe, cuts or abrasions from contaminated
items and animal bites, inhalation of aerosols generated by
accident or by work practices and procedures, contact between
mucous membranes and contaminated material (hands or surfaces),
and oral ingestion either as a result of inhalation mouth pipetting,
The source of exposure for the remaining cases (80%) could
not be determined. While some were believed to be due to exposure
to discarded glassware, handling infected animals, and clinical
specimens, etc., all that was known with any certainty was that
the individual had worked with the agent.
Most safety specialists believe that exposure to infectious
aerosols was responsible for the majority of these exposures/illnesses.