A Study of HIV Seroconversion in Health Care Workers After Percutaneous Exposure
ABSTRACT & COMMENTARY
Synopsis: In this study, zidovudine was almost certainly effective in preventing some HIV infections but is not 100% successful.
Source: Cardo DM. N Engl J Med 1997;337:1485-1490.
This article reports the results of a case-control study that attempts to examine the effect of zidovudine prophylaxis. The cases were composed of 33 health care workers who had percutaneous exposure to HIV and who acquired HIV infection. The control population was composed of health care workers who also experienced percutaneous exposure to HIV but did not seroconvert. The cases were from the United States, France, the United Kingdom, and Italy. The controls were drawn solely from the United States.
Cardo and associates collected as much information as was available concerning the type of exposure, the condition of the patient from whom the exposure was acquired, the type of device involved, the use of protective materials, and the severity of the injury.
Univariate analysis found that the risk of HIV transmission was markedly increased when the following factors were present: large diameter needle injury; deep injury; visible blood on the device; device placed in HIV patient's vein or artery; emergency procedures; or terminal illness in patient.
Hollow needle exposure was significantly worse than suture needle exposure, though the study included only three cases in which incidents other than hollow needle exposures occurred. Interestingly, there was no difference by univariate analysis in the risk of developing HIV infection if zidovudine was used.
The investigators then performed a logistic regression analysis to help eliminate confounding variables. When this analysis was completed, the following risk factors were identified: deep percutaneous injury; visible blood on injuring device; procedure involving needle in artery or vein; terminal illness in source-patient; or failure to use zidovudine prophylaxis.
Cardo et al conclude that zidovudine was almost certainly effective in preventing some HIV infections but is not 100% successful.
COMMENT BY KENNETH NOLLER, MD
This is an interesting paper that has great importance for all of us who care for HIV-infected patients. I was somewhat surprised that it did not receive greater coverage in the lay press, but, since it dealt only with health care workers, perhaps it was of insufficient interest to a wide audience.
During the past several years, great emphasis has been placed on the need for randomized, prospective, placebo- controlled trials to determine whether treatments are effective. Unfortunately, such trials are often impossible. While it would be useful and important to know with great certainty whether zidovudine protects a health care worker who has had an inadvertent percutaneous injury from a sharp object from an HIV-infected patient, no prospective, randomized trial will ever be completed. Such a trial was started but was soon abandoned because the great majority of health care workers refused to be randomized into the non-treatment arm.
Cardo et al performed a case-control study. While such a methodologic approach lacks the rigor of a prospective study, it is, nonetheless, a powerful technique for assessing risk factors for rare diseases-in this case, HIV infection following a needlestick injury. While there are always ways to criticize case-control studies (and, in this paper, Cardo et al provide a very complete list of limitations of their study), the results of most well-done case-control studies are believable and often important.
Based on the results of this study (and the effectiveness of zidovudine for fetal protection), any of us who experience a puncture from any instrument that likely contains any amount of blood from an HIV-infected patient should immediately be placed on zidovudine prophylaxis. While the drug does not entirely eliminate the possibility of infection, it does appear to result in a marked reduction in the likelihood that the injured clinician will develop HIV infection.
(Dr. Noller is Professor and Chairman, Department of OB/GYN, University of Massachusetts Medical Center, Worcester.)
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