compounds. Physical cleaning is often the most important step in a disinfection process, and even a rigorous disinfection procedure may not inactivate contaminating bacteria or viruses if these are protected by organic material, such as blood.

Bleach is a solution of sodium hypochlorite, and it exerts rapid and broad-spectrum disinfecting action (Hugo and Russell, 1982; Ingraham, 1992; Klein and Deforest, 1965a, 1965b; Rutala and Cole, 1984; Rutala, 1990; Van Houton and Hayre, 1991). Sodium hypochlorite solutions in concentrations of 0.05 to 0.5 percent (500-5,000 milligrams per milliliter) free and available chlorine are generally considered to be intermediate-level disinfectants and are among the most effective, most convenient, and least expensive germicides. The precise mechanism through which bleach exerts its germicidal action is not known, but it is believed to be mediated by the ability of free chlorine to denature proteins, inactivate sulfhydryl-containing enzymes, and damage nucleic acids (RNA and DNA).

Household bleach manufactured in the United States contains approximately 5 percent sodium hypochlorite (50,000 milligrams per milliliter chlorine [Cl2]). Bleach solutions exhibit sporicidal activity, are tuberculocidal, inactivate vegetative bacteria, and are fungicidal and virucidal. Klein and Deforest (1963) reported that 25 viruses tested, including picornaviruses, were inactivated within 10 minutes by as little as 0.02 percent (200 milligrams per milliliter) available chlorine.

The efficacy of a bleach solution to act as a disinfectant is determined by the concentration of free and available chlorine present in the solution (Klein and Deforest, 1965a, 1965b; Rutala and Cole, 1984; Rutala, 1990; Van Houton and Hayre, 1991). Chlorine demand is a term used to describe the amount of chlorine that is expended in the course of reaction with inorganic and organic materials. After this demand is met, any remaining chlorine is referred to as available chlorine . The level of available chlorine present to effect disinfection is influenced by a number of variables, including the amount of organic material in the infectious material and the temperature, pH, and hardness of the water used to dilute the bleach solution. Serum proteins and other organic material in blood will reduce the chlorine in bleach available for microbial inactivation (Favero and Bond, 1991; Klein and Deforest, 1965a; Rutala and Cole, 1984; Rutala, 1987). In practice in the health care setting, it is thus recommended that blood-contaminated surfaces first be cleaned to remove as much visible blood as possible prior to treatment with bleach.

The disinfectant potential of a bleach solution is not constant; rather, it decreases with time because of the relative instability of the active chlorine component. Bleach solutions lose potency at an accelerated rate when exposed to sunlight, oxygen, and heat. Bleach solutions prepared with tap



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