water at pH 8 or greater are stable for about one month when stored at room temperature in a closed, opaque container.

Susceptibility of HIV to Disinfection

Microorganisms vary widely in their level of resistance to chemical germicides (Favero and Bond, 1991; Hugo and Russell, 1982; Rutala and Weber, 1987; Klein and Deforest, 1965a). The types of microorganisms present can have a significant effect on the contact time and the concentration of germicide necessary to ensure the sterilization or disinfection of a contaminated object. Among pathogenic microorganisms, bacterial spores are the most resistant to sterilization and disinfection. In general, the presence of lipid in a virus is associated with a high degree of susceptibility to all germicides. The blood-borne pathogens HIV and HBV both are surrounded by lipid-containing membranes and thus are expected to be among the microorganisms least resistant to disinfection and sterilization. In principle, and in practice in the laboratory and the health care environment, there is no reason to believe that HIV is resistant to disinfection (Conte, 1986; Centers for Disease Control [CDC], 1987).

The identification of HIV as the cause of AIDS and the availability of tissue culture models to study virus infectivity permitted the laboratory evaluation of methods to disinfect HIV present on surfaces. The primary goal of the initial studies of disinfection methods was to determine the optimal approaches to disinfect reusable medical devices and to safely clean surfaces contaminated with blood from HIV-infected patients. Although varying in their precise protocols, all early studies were performed using HIV obtained from the supernatants of virus-infected tissue culture cell lines (Spire et al., 1984; Resnick et al., 1986; Martin et al., 1985). The virus present in such supernatants is not associated with infected cells, and this is referred to as cell-free virus. The infectious titer of cell-free HIV found in tissue culture supernatants ranges from 104 to 106 tissue culture infectious doses (TCID) per milliliter volume; these titers are several orders of magnitude higher than those typically present in the blood of HIV-infected individuals (Pantaleo et al., 1993). In addition, the amounts of proteins and other organic materials present in tissue culture fluids are usually less than those found in blood.

It is important to emphasize that preparations of cell-free HIV may demonstrate significantly different levels of susceptibility to disinfecting agents than samples of virus-infected cells, particularly as they may be found in blood specimens that are rich in cellular and extracellular (plasma) protein content. Cell-free HIV derived from supernatants of tissue culture cells is most susceptible to disinfection, whereas infected cells (and possibly cell-free virus present in the plasma) contained within blood specimens



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