Reports on HIV/AIDS: 1990

JANUARY 26, 1990, MMWR, Vol. 39, RR-1: [inclusive page numbers]
Considerations Regarding Use of Zidovudine After an Occupational
Exposure
Risk of HIV infection after exposure
Evaluation of the risk of HIV infection after exposure should take into account
existing knowledge from prospective studies of exposed workers, which demonstrate
that on the average the risk of transmission of HIV per episode of percutaneous
exposure (e.g., a needlestick or cut with a sharp object) to HIV-infected blood is
approximately 0.4%. These studies also suggest that the risk of HIV transmission per
episode of mucous-membrane or skin exposure to HIV-infected blood is less than that
after a percutaneous exposure (7,18-21). The risk of HIV transmission after occupational exposure to body fluids other than blood, for which universal precautions are
recommended, is unknown. The risk of HIV infection for persons who take zidovudine
postexposure prophylaxis cannot be determined at present because of the small
number of persons studied.
Risk evaluation should also include an assessment of factors that may increase or
decrease the probability of HIV transmission after an individual occupational exposure. These factors are not well understood, but include the likelihood that the source
fluid contained HIV and probably also the concentration of HIV in the source fluid, the
route of exposure, and the volume of fluid involved. For example, a percutaneous
exposure to concentrated HIV in a research laboratory is probably more likely to result
in transmission of infection than a similar exposure to HIV-infected blood in a clinical
setting. A percutaneous exposure to HIV-infected blood is probably more likely to
result in transmission than a mucous-membrane exposure to the same blood. Finally,
an exposure to a larger quantity of HIV-infected blood, such as injection of several
milliliters, is probably more likely to result in HIV transmission than an exposure to a
smaller quantity of the same blood, such as in a needlestick exposure.
Interval between exposure and initiation of prophylaxis, if given
Data from animal studies suggest that prophylaxis against certain retroviral
infections other than HIV may be more effective when started within hours after
exposure (22,23). Because in vitro studies indicate that human HIV infection may be
established in human lymphocytes within hours after exposure (24), and epidemiologic studies of exposed health-care workers indicate that acute retroviral illness may
occur as early as 2 weeks after exposure (7), it appears that if the decision is made to
use postexposure prophylaxis, prophylaxis should be initiated promptly.
Counseling and informed consent
If zidovudine prophylaxis is being considered, the worker should be counseled
regarding a) the theoretical rationale for postexposure prophylaxis, b) the risk of
occupationally acquired HIV infection due to the exposure, c) the limitations of current
knowledge of the efficacy of zidovudine when used as postexposure prophylaxis,
d) current knowledge of the toxicity of zidovudine (including the data from animal and
human studies) and the limitations of this knowledge in predicting toxicity in
uninfected individuals who take the drug after occupational exposures, and e) the
need for postexposure follow-up (including HIV serologic testing), regardless of
whether zidovudine is taken. The worker should also be informed that there are
diverse opinions among physicians regarding the use of zidovudine for postexposure

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