HIV and the Health Care Worker
ABSTRACT & COMMENTARY
Source: Cardo DM, et al. A case-control study of HIV seroconversion in health care workers after percutaneous exposure. N Engl J Med 1997;337:1485-1490.
The risk-benefit ratio of zidovudine prophylaxis after occupational percutaneous exposure to HIV-infected blood has been a subject of much debate. It is well-known and accepted that the overall risk of seroconversion in such instances is 0.3 percent; however, specific data on factors that influence seroconversion risk have been intuitive but not well-documented. In this case-control study of occupational, percutaneous exposure to HIV-infected blood, Cardo and colleagues sought to define those factors that significantly affect seroconversion, including the use of zidovudine prophylaxis.
Case patients were identified as health care workers with documented occupational percutaneous exposure to HIV-infected blood and temporally associated HIV seroconversion without other identifiable reasons for seroconversion. Controls were health care workers who sustained percutaneous exposure to HIV-infected blood but remained HIV seronegative at least six months later.
Thirty-three case patients were identified through national surveillance systems at the Centers for Disease Control and Prevention (CDC) and through similar networks in France, Italy, and the United Kingdom. Six hundred seventy-nine case controls were identified through the CDC Needlestick Surveillance Project. Four factors proved to have statistically significant influence on HIV transmission: deep injury, injury with a device visibly contaminated with source-patient blood, exposure to needles placed in the source-patient’s vein or artery, and source-patient terminal illness (defined as death of the source-patient from AIDS within two months after health care worker exposure). In addition, after controlling for factors affecting HIV transmission, seroconversion rates were reduced by 81% (95% CI; 48-94%) in health care workers who took prophylactic zidovudine. Cardo et al conclude that larger volumes of source blood, especially with high HIV titers, increase the risk of HIV seroconversion after percutaneous exposure, and that zidovudine prophylaxis appears to offer a protective advantage in exposed patients.
COMMENT BY FREDERIC KAUFFMAN, MD, FACEP
Prior to this data becoming available in 1995 in the Morbidity and Mortality Weekly Report, my institution recommended that individuals exposed to HIV-infected blood via percutaneous routes be counseled and educated on the pros and cons of post-exposure prophylaxis; however, no formal policy regarding prophylaxis recommendation was in effect. Though individuals involved in infection control may have had strong opinions one way or the other, there was not enough definitive evidence available to make an absolute recommendation. All of that changed when this data became available. Now, post-exposure chemoprophylaxis is officially recommended, and great efforts are made to ensure an efficient system of evaluation that allows for the institution of prophylaxis within one hour of exposure. The details of this study appear in this issue of the New England Journal of Medicine and further substantiate what many have believed for several yearsthat zidovudine prophylaxis reduces the risk of HIV seroconversion.
It can be argued that a case-control study does not prove the point in question. Indeed, in order to do so, a prospective, randomized, placebo-controlled trial would be needed. However, to detect a significant change in an end point that occurs in only 0.3 percent of cases, thousands of subjects would be required, and no such study appears to be on the horizon. Considering the nature of this clinical problem, the emotional effect of exposure to HIV-infected blood, and the information provided in this study, I have become a believer in post-exposure prophylaxis.
Factors associated with increased risk of seroconversion after percutaneous exposure to HIV-infected blood include:
a. both deep wounds and wounds that scratch the skin but do not cause bleeding.
b. exposure to a source patient who died of any cause in the subsequent six months.
c. injury with a device visibly contaminated with blood.
d.. exposure to arterial but not venous blood.
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