18. Decontamination and Disinfection

Decontamination	- a routinely required step of destroying/inactivating microorganisms in microbiological laboratories to protect laboratory workers and prevent contamination of their work. This is the destruction or removal of microorganisms to some lower level, but not necessarily total destruction. Sterilization, disinfection and antisepsis are all forms of decontamination.
Disinfection	- implies the use of antimicrobial agents, chemical products usually, to inanimate objects (e.g., work surfaces, equipment, etc.) to destroy all organisms that could pose a potential hazard to humans or compromise the integrity of the experiment.
Sterilization	- the process of destroying or removing all living organisms and viruses, usually by steam or gas autoclaving.
Antisepsis	- the application of a liquid antimicrobial chemical to living tissue to prevent growth or destroy potentially infections organisms. Antiseptics are formulated for use on skin, and should not be used as disinfectants.

General Considerations:

• Choose a disinfectant that is not corrosive or otherwise destructive to the items undergoing decontamination.
• Read and follow the manufacturer's label directions concerning the recommended disinfectant concentration, contact time and method of application. For large spills of cultured or concentrated infectious agents (BL2), add undiluted bleach directly to the spill. The total volume of bleach added should be 1/10 the total spill volume. The bleach will reduce the hazard involved in spill clean-up by reducing the titer of the infectious agents. For small spills of BL1 cultures, or for blood/body fluid spills, it is expedient to clean-up the material using a detergent disinfectant product and then to disinfect with a 1:10 bleach solution.
• Wear the appropriate gloves and eye protection whenever using chemical disinfectants.
• Determine if the design of the equipment, or its construction materials, will have an effect on the decontamination process. Crevices, joints and pores constitute barriers to the penetration of liquid disinfectants. Prolonged contact time may be required to accomplish decontamination, depending on the intricacy of the design and the amount of soil present.
• Select an appropriate disinfectant contact time. The longer the exposure to the chemical agent, the more likely that all pertinent microorganisms will be inactivated. A contact time of 10 minutes may not be adequate to disinfect an item, especially one that is difficult to clean because of narrow channels or other areas that can potentially harbor microorganisms. Longer exposure times, i.e. 20 to 30 minutes, may be necessary. This is especially true when high-level disinfection is to be achieved
• Bleach and other disinfectants are less effective in the presence of proteinaceous material. Organic material including blood and soil, may inactivate chemical disinfectants and protect microorganisms from the decontamination process. After clean-up of a large spill in which the concentration of pathogenic organisms has been reduced by the addition of bleach, the area should be wiped with FRESH disinfectant to assure that all organisms have been inactivated.

Decontamination Procedures:

• Decontamination of liquid waste:
  1. Using Iodophor solution – leave for 24hr from the last spill.
  2. Using Hypochlorite solution. (Bleach) 1:10 – leave for1hr. from the last spill.
  After decontamination pour into the sink.
• Disinfection (cleaning) of equipment before repair:
  1. Wipe it with bleach solution 1:100.
  2. Allow 5 minutes contact with the solution.
  3. Wipe with a clean paper towel.
  4. Clean with 70% alcohol.
  5. Place sticker signed by the group head that it is clean of biohazard.

Disinfectants suitable for decontaminating the surfaces of scientific equipment include the following generic formulations: glutaraldehyde; iodophors; chlorine compounds; alcohol (isopropyl, ethyl); phenolic compounds and quaternary ammonium compounds.

Methods of Disinfection:

Method	Concentration or level a	Activity level
HEAT:
Moist heat	75 - 100° C	High
LIQUIDS:
Glutaraldehyde, aqueous b	2%	High
Hydrogen peroxide, stabilized	2%	High
Formaldehyde, aqueous c	1-8%	High
Iodophors d	30-50 mg. of free iodine per liter; 70-150 mg of available iodine per liter	Intermediate
Chlorine compounds e	500-5,000 mg of free chlorine per liter	Intermediate
Alcohol (ethyl; isopropyl) f	70%	Intermediate
Iodine and alcohol	0.5% + 70%	Intermediate
Phenolic compounds, aqueous	0.5-3%	Intermediate
Quaternary ammonium compounds, aqueous	0.1-0.2%	Low

1. For sterilization, see the recommendation of the manufacturer for exposure times and conditions. For disinfection, exposure times should be 20 to 30 min. or longer.

2. There are several glutaraldehyde-based proprietary formulations on the U.S. market, i.e., low- neutral-, or high-pH formulations, recommended for use at normal or raised temperatures with or without ultrasonic energy, and also as a formulation containing 2% glutaraldehyde and 7% phenol. Instructions of the manufacturer regarding use as a sterilant, disinfectant or regarding anticipated dilution during use, should be closely followed.

3. Due to the ongoing controversy surrounding formaldehyde as a potential occupational carcinogen, the use of formaldehyde is recommended only in limited circumstances under carefully controlled conditions, i.e., for the disinfection of certain hemodialysis equipment.

4. Only those iodophors registered with the EPA as hard-surface disinfectants should be used. The instructions of the manufacturer regarding proper use dilution and product stability should be closely followed. Antiseptic iodophors are not suitable for use as disinfectants.

5. There currently is a formulation registered with the EPA as a sterilant and disinfectant, depending on contact time, whose active ingredient is chlorine dioxide. The instructions of the manufacturer regarding use as a sterilant or disinfectant or regarding anticipated dilution during use should be closely followed.

6. Volatile products such as alcohols, require careful attention to ensure proper contact time during a disinfection protocol.

7. A useful link for information about decontamination is http://www.nih.gov/od/ors/ds/pubs/biodecontamination/.