Unusual transmissions of blood-borne viruses, with special reference to HIV.

Containing virus infections in hospital and other clinical contexts depends upon a clear understanding of how they may be transmitted. The routes of transmission, infectious doses, portals of virus entry and exit, intensity of virus excretion and stability of the virus in the environment are all important considerations. Although present infection control policies may be based on the best available evidence, the risks are in some instances still not well enough defined to be sure that all reasonable precautions are in place. One way of improving infection control policies is to study unexpected and unusual viral transmissions to see whether new or previously unrecognized hazards have arisen. Examples are given where transmission of HIV and other blood borne viruses has seemed to occur outside recognized risk situations. On closer examination most of these represent known transmission modes but, where they do not, current control of infection policies may need to be reviewed.