Past and present hazards of working with infectious agents.

Over 4,000 cases of laboratory-associated infection have been recorded. Some of the agents involved often in the past have been less frequently the cause of such infection in recent years, and some agents are more likely to infect those working with them than others. Pipetting, the use of a needle and syringe, and spills have been most frequently involved in accidents resulting in infection, but in the majority of cases no recognized accident occurred. In these instances, infectious aerosols, produced in various ways, are probably the most frequent causes of laboratory-associated infection. The introduction of protective devices and emphasis on safe procedures seem to be reducing the risk of accidental infection. Although work with tumor viruses and recombinant DNA research may not be as hazardous as was originally feared, continued caution and surveillance is advised.