A review of existing research confirms that health-care workers should undergo a month of preventive drug treatment if they are exposed to HIV on the job.
Still, the reviewers say that there's been little research into so-called occupational postexposure prophylaxis, and it's still not clear what should be done when health-care workers are exposed to patients who are resistant to some drugs.
The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.
Doctors, nurses and other health-care providers have worried about HIV exposure since the AIDS epidemic first began in the early 1980s. Since the virus that causes AIDS is transmitted through blood, a simple needle stick could infect anyone treating a patient.
The risk, however, is quite low. The Centers for Disease Control and Prevention estimated in 2005 that the risk of HIV transmission through a contaminated needle stick is 0.3 percent, or about 1 chance in 333.
The low transmission risk may be related to two factors - the small amount of virus that gets into the body through health-care workers' wounds and the barrier to the virus posed by the lower levels of the skin, said review co-author George Rutherford, M.D., of the University of California, San Francisco's Institute for Global Health.
Still, a 1-in-333 risk is hardly insignificant. Many countries recommend postexposure prophylaxis, or PEP - in which doctors try to kill the virus in the body before it takes hold - if a health-care worker has been potentially exposed to HIV. The same approach is used to treat people who have been potentially exposed to HIV through sex.
The low number of actual cases of infection makes it difficult for researchers to find enough people to study the effectiveness of postexposure treatment, Rutherford said. He added that, not surprisingly, exposed health-care workers haven't been willing to take part in any study that might result in their taking a placebo instead of drug treatment.
The researchers were only able to find a single study that compared those who took drugs after exposure to those who didn't.
That study, of 712 exposed health-care workers, found that the odds of becoming infected with HIV were reduced by about 81 percent among those who took zidovudine - an anti-HIV drug also known as AZT or Retrovir - after exposure. The study also reported that the odds of HIV infection were higher if a health-care worker had a deep injury, if there was visible blood on the device (such as a needle), if the needle had been placed in the infected patient's blood vessel or if the patient was terminally ill. A deep injury appeared to be by far the most dangerous of the factors.
HIV patients typically take more than one drug, and doctors prescribe multiple drugs as prophylaxis for exposed health-care workers, too. While there's no research suggesting whether that's a good idea in the latter case, the reviewers still recommend a multiple-drug regimen because it works in HIV-infected patients.