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Decontamination and Disinfection

Terminology

sterilization - the destruction of all microbial life, including bacterial endospores.

disinfection - the elimination of virtually all pathogenic microorganisms on inanimate objects with the exception of large numbers of bacterial endospores, reducing the level of microbial contamination to an acceptably safe level.

antisepsis - the application of a chemical to living tissue to prevent infection.

decontamination - all of the above. Decontamination is any activity that reduces the microbial lode to prevent inadvertent contamination or infection. The appropriateness of a decontamination procedure is situationdependent. For example, surgical instruments must be sterile but this level of microbial killing is unnecessary for Environmental surfaces such as floors and walls.

Disinfection

Disinfection encompasses a continuum of outcomes in terms of the types of organisms destroyed. Microorganisms can be grouped as following in terms of decreasing resistance to disinfectants: bacterial endospores (B. subtilis, clostridium spp); Mycobacteria; nonlipid or small viruses (poliovirus, rhinovirus); fungi ; vegetative bacteria; and, lipid or medium sized virus (herpes simplex, HIV, HBV).

The table at the end of this section provides a framework for the selection of the appropriate disinfectant. The label on a commercial product will note its type of ‘cidal’ action (‘tuberculocidal’, ‘sterilant’). These claims may not appear unless the manufacturer has submitted data to the EPA supporting such claims. The lists of EPA registered disinfectants can be obtained from your campus EH&S office or found at http://www.epa.gov/oppad001/chemregindex.htm

The EPA does not independently audit such results and research indicates that in real life situations some products do not perform as claimed. This result from manufacturers testing their products in best-case situations, e.g., on a smooth surface, at an optimal pH, in a buffer solution instead of a solution containing organic material which partially inactivates some disinfectants. For high risk pathogens, investigators may devise their own test to confirm a product’s claim or consult EH&S.

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When using any disinfectant:

  • Follow label instructions for dilution and contact time needed for desired level of disinfection.
  • Disinfectants that require pre-use dilution should be treated as hazardous chemicals during mixing. Wear a lab coat, the correct type of chemical-resistant glove, and goggles, not glasses.
  • Clean contaminated surfaces as soon as possible and any surface that may have become contaminated at the end of the task..
  • Select the disinfectant with the lowest toxicity possible
Considerations for selecting and using disinfectants
  • Nature of surface-rough surfaces require a longer contact time than smooth ones.
  • Surface compatibility-bleach will corrode many metals, rinse with water after use; instruments vary in their ability to withstand disinfectants based on their composition.
  • Organic matter will inactivate some disinfectants; a second application may be necessary once visible contamination (and hence, most organic debris) has been removed. The removal of visible ‘soil’ may be the single most critical factor in assuring effective decontamination.
  • Resistance of microorganisms, e.g. bacterial endospore vs. vegetative bacteria.
  • Number of microorganisms present, overnight culture vs. a recently inoculated one.

The Bloodborne Pathogens Standard requires that products labeled "tuberculocidal hospital disinfectant" be used on surfaces and equipment when the Standard is in force. Household bleach, usually at a 1/10 dilution, also satisfies this requirement and may be used in these cases. Bleach solutions lose potency over time and should be prepared fresh daily.

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Summary of Disinfectant Activities

Disinfectant

Disinfection Level

Bacteria

Lipophil.

Viruses

Hydro-

Philic

Viruses

M. tuber- culosis

Fungi

Comments

Alcohols (ethyl and isopropyl)

60-85%

intermediate

+

+

-

+/-

+

Not sporicidal; evaporates quickly so that adequate contact time may not be achieved, high concentrations of organic matter diminish effectiveness; flammable.

Phenolics (0.4%-5%)

intermediate

+

+

+/-

+

+

Not sporicidal; phenol penetrates latex gloves; eye/skin irritant; remains active upon contact with organic soil; may leave residue.

Glutaraldehyde

(2-5%)

high

+

+

+

+

+

Used to sterilize surgical instruments that can not be autoclaved; strong odor; sensitizer; use with adequate ventilation. Not for use on Environmental surfaces.

Quaternary Ammonium

(0.5-1.5%)

low

+

+

-

-

+/-

May be ineffective against Psuedomonas and other gram – bacteria; recommendation limited to Environmental sanitation (floors, walls). Low odor, irritation.

Iodophors

(30-1,000 ppm iodine)

intermediate

+

+

+

+/-

+/-

Inactivated by organic matter.

Chlorine (100-1,000 ppm)

intermediate

+

+

+

+/-

+

Not sporicidal; inactivated by organic matter; fresh solutions of hypochlorite (chlorox) should be prepared monthly; corrosive; irritating to eyes and skin.

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