cultures of T lymphocytes or macrophages for HIV isolation. The impact of the choice of indicator cells on the sensitivity of virus detection following disinfection is not known.

Spire and colleagues (1984), using an assay for the presence of HIV reverse transcriptase activity (and not the residual infectivity of the virus preparation itself), examined the inactivation of cell-free HIV by commonly used disinfectants. Their results suggested that 25 percent ethanol or 1 percent glutaraldehyde should be sufficient to disinfect medical instruments, and that 0.2 percent sodium hypochlorite should be sufficient to disinfect contaminated environmental surfaces. They also reported that HIV was inactivated by a 1:400 dilution of beta-propiolactone or 30 millimolar sodium hydroxide, but that formalin 0.1 percent required 48 hours to render reverse transcriptase activity undetectable.

Resnick and colleagues (1986) pointed out that assays for reverse transcriptase activity are not reliable alternatives to tests for infectious virus. These authors, using concentrated preparations of cell-free HIV, found that infectious virus could be recovered from dried material for 3 to 7 days. In an aqueous environment, cell-free HIV retained its infectivity for more than 2 weeks at room temperature. However, HIV infectivity was completely eliminated following 1 minute of exposure to sodium hypochlorite 0.5 percent (a 10 percent solution of household bleach), alcohol 70 percent, or a 0.5 percent solution of the detergent NP-40.

Martin and colleagues (1985), using antigen detection methods to monitor virus replication in tissue culture, reported that cell-free HIV could be inactivated by a variety of disinfectants at concentrations well below those commonly employed. They reported that HIV infectivity was efficiently inactivated by 0.3 percent hydrogen peroxide, 50 percent ethanol, 0.5 percent paraformaldehyde, 0.5 percent Lysol (a proprietary mixture of phenolics and surfactants), and a 1/1,000 dilution of household bleach (approximately 50 milligram per milliliter chlorine). Since that time, many laboratories have performed HIV inactivation studies with various compounds. The results of many of these studies have been reviewed by Sattar and Springthorpe (1991) and confirm the predicted susceptibility of HIV to inactivation by a wide variety of chemical disinfectants.

CDC Recommendations

Based on the results of these early studies, recommendations were formulated by the Centers for Disease Control for the sterilization, disinfection, and housekeeping procedures in health care settings (Centers for Disease Control, 1987). These guidelines continue to serve effectively and have not been modified. An example of an effective disinfection procedure used in the health care environment relevant to the consideration of inactivation



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