Disinfection

05/01/23 DISINFECTION 1

DISINFECTION

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OVERVIEW

DEFINITIONS CLASSIFICATION PHYSICAL AGENTS HEAT RADIATION FILTRATION CHEMICAL AGENTS TYPES OF DISINFECTANTS BLOOD SPILLS DISINFECTION OF SURFACES DISINFECTION OF SAFETY CABINETS DISINFECTION OF ROOMS DISINFECTION OF SKIN TESTING OF DISINFECTANT DISINFECTION POLICY


DEFINITIONS

DISINFECTION- It is a process which reduces the number of contaminating microorganisms, particularly those liable to cause infection, to a level which is deemed no longer harmful to health.

ANTISEPSIS- It is used to describe disinfectants applied to living tissue such as wound.


Contd.

DECONTAMINATION It is a general term for the treatment used to make

equipments safe to handle by freeing them of microbiological, chemical, radioactive and other contaminants.


CLASSIFICATION OF DISINFECTION

DISINFECTANT

PHYSICAL AGENT

HEAT

RADIATION

HALOGENS SURFACE ACTIVE SUBSTANCES

CHEMICAL AGENT

FILTERATION

BIGUANIDEALCOHOL

PHENOL AND PHENOLIC COMPOUNDS


PHYSICAL AGENTS

1. HEAT i. Dry Heat

a. Flaming ii. Moist Heat:-

a. Temperature below 1000C b. Temperature at 1000C c. Steam at 1000C


Temperature below 1000C1.Vaccine bath2. Inspissation3. Pasteurization ~Low temperature holding method

~High temperature short time


Temperature at 1000C Boiling Tyndallisation


Steam at 1000C


PASTEURIZATION


2. RADIATION

Radiation sterilization: Ultra Violet rays are used

to disinfect hospital operating rooms and safety

cabinets.


3. FILTRATION

It is the method of removal of bacteria from heat labile liquids such as sera and antibiotics solution.

Factors affecting its efficiency are: - Initial number of microorganisms

- type of microorganism - composition and pore size of the filter


Contd..

Uses:

a. Separation of toxins and other soluble products of bacterial growth.

b. Sterilization of materials or other materials.

c. Purification of water.


TYPES OF FILTERS

I. CANDLE FILTERS

II. ASBESTOS FILTER e.g. Seitz filter Carlson and sterimat filter Disadvantages:

III. SINTERED GLASS FILTER


iv. MEMBRANE FILTERpore size range from 0.015-12micrometers

Uses: i. Preparation of solution for parenteral use. ii. Disinfection of solution by removing bacteria and yeast.

v. SYRINGE FILTER Uses: Disinfection of small volumes of fluids.


vi. PRESSURE FILTER

Uses: For the production of water for lab use.


HEPA FILTERS High efficiency particulate air

filter (HEPA) are filters that are capable of removing 99.97% of particles that are 0.03micron or larger.

These work by forcefully pushing air through filters made of microscopic glass fibers, similar in thickness and texture.


They help in removing pollen, dust mites, molds.


CHEMICAL METHODS

Many chemical agents are used as disinfectants and antiseptics


Properties of an ideal disinfectant or antisepticIt should Have wide spectrum of activity

Act in the presence of organic matter

Have high penetrating power

Be stable and effective in acidic and alkaline conditions


Not be corrosive

Not be toxic and irritant

Be safe, easy to use and cost effective

Have long shelf life


GENERAL RULES FOR USE OF DISINFECTANTS

1. Disinfectants are generally toxic and may damage or irritate the skin, conjunctiva and mucosa. Care must be taken to avoid contact with irritant or toxic concentration. Disposable gloves should be worn when handling them.


Contd..

2. A disinfectant may have narrow spectrum of activity against different kinds of microorganisms. It is necessary therefore to choose a disinfectant that issuitable for the purpose. Each laboratory should have a written disinfectant policy specifying the kind and concentration of disinfectant for each type of use.


Contd..

3. Disinfectants must always be used at the correct concentration. Too little is ineffective and too much may be irritant to skin.

4. The life of disinfectant varies with its formulation and many disinfectants deteriorates when diluted with water. Working solution should be renewed each day.


Contd..

5. Disinfectants take time to act. The time for effective disinfection will vary with the

• microbial load • presence of organic material• the pH• the nature of exposed surfaces and• the presence of resistant bacteria or spores.


Contd..

6. Disinfectants may not kill even susceptible bacteria if ~ microbial load is large.

~ if there is excessive organic matter. ~ if whole surface area to be decontaminated is

not covered.


Contd..

7. Certain disinfectants are easily inactivated by~ change in pH~ by the presence of soap or detergents ~ by the presence of cotton, cellulose and other discard materials.


FACTORS AFFECTING PERFORMANCE OF DISINFECTANTS

Microbial load

Characteristics of microorganisms

Nature of exposed surfaces

Presence of organic materials


Contd.

Concentration and stability of agents

pH- Glutaraldehyde is more stable under acidic condition while the activity of phenol reduces at alkaline pH

Time and temperature of exposure


TYPES OF DISINFECTANTS

1. HIGH LEVEL DISINFECTANTSExamples: Aldehyde, gases

Uses: for endoscope and surgical instruments

2. INTERMEDIATE LEVEL DISINFECA NTSExample: alcohol, iodophore Uses: laryngoscope


contd.

3. LOW LEVEL DISINFECTANTS

Example: quaternary ammonium compounds Uses: electrocardiogram, stethoscope


II. CHEMICAL AGENTS

ALDEHYDESa. Formaldehyde

b. Glutaraldehyde

ALCOHOLSa. Ethyl alcoholb. Isopropyl alcoholc. Methyl alcohol



C. BIGUANIDE Chlorohexidine: ~ Less irritant and toxic to skin. ~ Commonly used as a skin disinfectant ~ Less active against Gram negative bacteria.


HALOGENS

i. Chlorine and Hypochlorite: Both are widely used as disinfectants.

Hypochlorites are inorganic chlorine containing compounds. Have bactericidal, fungicidal, virucidal and sporicidal action

ii. Iodine- Used as skin disinfectant. Actively bactericidal but

moderate action against spores.


PHENOL AND PHENOLIC COMPOUNDS

Phenol and phenolic compound are effective disinfectants. Phenolic compound like bis-phenol Hexachlorophane has particular activity against Gram positive cocci.


Contd..

Mode of action-

a. Physical damage to cell membrane

surface.

b. Precipitation of cell protein

c. Inactivation of enzyme


SURFACE ACTIVE AGENTS

These are substances that reduces surface tension.

Anionic, cationic, non-ionic and amphoteric

detergent are used generally.


Hydrogen peroxide

Peracetic acid


BLOOD SPILLS

GENERAL INFORMATION

a. Universal precautions must be observed.

b. When there is blood spills, access to the area should be limited.


Contd..

c. Only disposable towels, tissue papers should be used.

d. If a spill involves a broken glassware, glass should not be picked up directly with the hands. It must be cleaned up by mechanical means such as brush, forceps.


PERSONAL PROTECTIVE EQUIPMENTS

Person who cleans blood spills should wear disposable gloves.


DISINFECTANTS

a. A solution of 5.25% sodium hypochlorite diluted between 1:10 and 1:100 with water.

b. For viruses the effective concentration are those containing 10,000 parts per million (ppm) for spillage and 1000 ppm for cleaning.


DISINFECTION OF SURFACE

Freshly prepared solution of disinfectant should be available on every microbiology work bench. Liquid spillage should be immediately treated and if the spillage is large germicidal powder (precept granules) should be added.

Surface disinfectant that are used are: i. Phenolicsii. Hypochloriteiii. Glutaraldehydeiv. Ethyl alcohol


DISINFECTION OF SAFETY CABINETS

Safety cabinets can be disinfected by using 40% formaldehyde vapour.

After exposure the formaldehyde vapours can be removed mechanically by switching on the

extract fan or through HEPA filters into exhaust duct

neutralized with ammonia by exposing 250ml ammonia per liter of formaldehyde used.


DISINFECTION OF ROOMS

Disinfection of laboratory rooms may be done

with 40% formaldehyde vapour, UV rays or HEPA

filters


Contd..

PROCEDUREa. Before fumigation seal the room with adhesive

tape round the edges of door and windows to prevent leakage.

b. For each 1000 cubic feet of space, 500ml 40% formaldehyde solution and 1 liter water in an electric boiler with a safety cut out when boiling dry and a time switch. Set the latter to open just before evaporation is completed. Switch on the boiler.


Contd..

c. Leave the room filled with formaldehyde and

seal for 24hour.

d. Open the door and enter the room with respiratory protective wearing, open window to allow vapor to dispense and neutralize any residual formaldehyde with ammonia by exposing 250ml of ammonia per liter of formalin used.


DISINFECTION OF SKIN

Laboratory staff must wash hands thoroughly after their work and after removing protective gloves, covering or clothing.

Washing with soap or water removes most of the transient surface contamination.

Small cuts or abrasions should be treated with soap and running water or a saline solution.


Contd..

Broken skin and wounds should be cleaned and irrigated with mild disinfectants like chlorohexidime with cetramide.

If the unbroken skin is grossly contaminated with bacteria or viral pathogen it should be rinsed with phenolic or hypochlorite disinfectant.


TESTING OF DISINFECTANTS

Rideal Walker Test Chick Martin Test In-Use tests


RIDEAL WALKER TEST Suspension containing equal number of Salmonella

typhi are submitted to the varying concentration of phenol and disinfectant is tested.

CHICK MARTIN TESTThe disinfectant act in the presence of organicmatter.


TESTING OF DISINFECTANTS

Rideal Walker and the Chick Martin tests compare the disinfectants with phenol for the ability to kill Salmonella typhi.

Phenol coefficients are appropriate only for phenolic disinfectants.

Hospital laboratories should perform the ‘in use’ test to confirm that the chosen disinfectant is effective under the condition and period of its use.


IN USE TEST

Used to monitor performance of a particular disinfectant and how it is being used

Samples of disinfectant solutions in use around the hospital are tested

It determines the survival and multiplication of contaminating pathogens in disinfectant solutions


DISINFECTION POLICY

The policy should consider the following The source for which the process is required. The processes and products available for

disinfection. The category of process required for each item The specific product and method to be used for

each item of equipment, the site of use and the staff responsible for the procedure.


REFERENCES Text book of microbiology – Anathanarayanan Review of medical microbiology and immunology

–Warren Levinson. Medical microbiology – Jawetz, Melinick, and

Adelberg. Microbiology- Pelczar and Noel R Kreig Fundamentals of microbiology - Tortora


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Disinfection

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