CDC publishes new data suggesting AZT efficacy

Health care workers at risk for occupational exposure to HIV infection should be informed about the use of zidovudine (AZT) for post-exposure prophylaxis -- including the latest data suggesting the drug may have some efficacy in preventing infection, the Centers for Disease Control and Prevention reports.1

"Analysis of these data suggested that use of [AZT] postexposure may be protective for health care workers," the CDC states. (See Hospital Infection Control, January 1996, pp. 12-14.)

The agency recommended that health care workers be informed of the risk for HIV transmission after exposure, factors that may increase or decrease this risk, "and the limited knowledge regarding the potential efficacy and toxicity" of AZT as a post-exposure prophylaxis. If a decision is made to use post-exposure prophylaxis, it should be initiated promptly, the CDC states.

The agency is evaluating the implications of the efficacy data study and other available information in assessing the possible need for revision of recommendations for managing occupational exposure to HIV -- particularly regarding post-exposure use of antiretroviral agents.

AZT is not approved by the Food and Drug Administration for use as post-exposure prophylaxis, and the CDC previously concluded a recommendation could not be made for or against the use of the drug following exposures to health care workers by HIV-infected blood.2

Study first to suggest AZT's effectiveness

Although failures of post-exposure AZT to prevent HIV infection in health care workers have been documented, the CDC study of health care workers exposed to HIV is the first that suggests effectiveness of AZT as a post-exposure prophylaxis.

The case-control study included 31 health care workers (23 from the United States, five from France, and three from the United Kingdom) and 679 control workers. Of the 31 exposures sustained by case-health care workers, 29 (94%) were needlesticks with hollow needles, and two (7%) involved other sharps. Of the 679 exposures sustained by control-workers, 620 (91%) were needlesticks (including 594 hollow and 26 solid needles), and 59 (9%) involved other sharp objects. AZT post-exposure prophylaxis was used by nine (29%) of the case workers and 247 (36%) of the controls.

Larger study preferable

After controlling for other factors associated with HIV transmission risk, the model indicates the risk for HIV infection among workers who used AZT was reduced by approximately 79%. The agency added the caveat that the optimal study would be a prospective, placebo-controlled trial, which has not been possible because of the requirement for a large number of health care workers and the relatively low rate of HIV seroconversion following occupational exposure.

Additional findings include increased risk of seroconversion following exposures to blood from source patients during the latter stages of AIDS, which is probably indicative of a higher titer of HIV in blood as the illness becomes terminal. The risk for HIV infection following percutaneous exposures to HIV-infected blood was also increased if the exposure involved a larger quantity of blood, as indicated by any of the following:

* a device visibly contaminated with the patient's blood;

* a procedure that involved a needle placed directly in a vein or artery;

* a deep injury.


1. Centers for Disease Control and Prevention. Case-control study of HIV seroconversion after percutaneous exposure to HIV-infected blood -- France, United Kingdom, and United States, January 1988-August 1994. MMWR 1995; 44:929-933.

2. Centers for Disease Control and Prevention. Public health service statement on management of occupational exposure to human immunodeficiency virus, including considerations regarding postexposure use. MMWR 1990; 39(no. RR-1). *