Sterilization, Disinfection and Antisepsis

Question 1

Goal of disinfection/sterilization

Answer 1

-reduce the numbers of microorganisms on a device to a level that is insufficient to transmit infectious organisms

Question 2

Healthcare-Associated Infections (HAI’s)

Answer 2

• if you are admitted to a hospital, you have a 5% chance of contracting an HAI
• 1.7 million people per year get an infection during a hospital stay
• your length of stay in the hospital increased by 17.6 days if you get an HAI
• over a quarter of all hospital-acquired HAIs are caused by four types of infections: pneumonia, bloodstream infection, surgical site infection, urinary tract infection

Question 3

HAI’s are associated with risk factors

Answer 3

• the use of indwelling medical devices such as bloodstream, endotracheal and urinary catheters
• transmission of communicable disease between patients and healthcare workers
• surgical procedures
• injections
• contamination of the healthcare environment
• overuse or improper use of antibiotics

Question 4

Challenges with HAIs

Answer 4

• reprocessing of medical devices is a challenge with respect to HAIs
• endoscopes is probably the most challenging reprocessing tast in health care
• flexible endoscopes have intricate sophistricated small parts that are difficult to clean before they can be disinfected

Question 5

History of Infection control

Answer 5

• Ignaz Semmelweis recommended chlorinated lime solution
• Florence Nightingal mortality rates in different wards
• Joseph Lister- clean wounds and dress them carbolic acid- first mostly sterile surgical field

Question 6

Sterilization

Answer 6

results in the complete destruction of all forms of microbial life, including bacterial and fungal spores

Question 7

Disinfection

Answer 7

-results in the destruction of specific pathogenic microorganisms- does not necessarily result in sterilization

Question 8

Antisepsis

Answer 8

-an agent is one that has been formulated for use on skin or mucous membranes to prevent or inhibit growth of microorganisms (Antiseptics should not be used to decontaminate inanimate objects)

Question 9

Decontamination

Answer 9

-removal of debris, blood, and proteins- and most microorganisms- not necessarily rendering the decive “safe to handle” by HCW’s who are not wearing protective attire

Question 10

High-level disinfection (HLD)

Answer 10

• destroys all micro-organisms except high numbers of bacterial spores.
• example: pasteurization and liquid immersion in chemical sterilants (used for heat sensitive semi-critical items such as GI endoscopes, bronchoscopes)

Question 11

Intermediate-level disinfection

Answer 11

• destroys vegetative bacterial, mycobacteria, most viruses, most fungi but not bacterial spores
• example: hospital disinfectant with label claim regarding tuberculocidal activity (e.g. chlorine-based products, phenolics-exposure times at least 30-60 seconds used on noncritical patient care items or surfaces with visible blood

Question 12

Low-level disinfection

Answer 12

• destroys vegetative bacteria, some fungi and viruses but not mycobacteria or spores hospital disinfectant with no tuberculocidal claim (e.g. chlorine-based products, phenolics, quatemary ammonium compounds exposure times at least 30-60 sec) or 70-90% alcohol
• used on noncritical patient care items (e.g. blood pressure cuff) or surfaces (bedside table) with no visible blood

Question 13

Factors that influence the degree of killing of microorganisms and the choice of disinfectant

Answer 13

• types of organisms
• number of organisms (bioburden)
• concentration of disinfecting agent
• presence of organic material (e.g. serum, blood)
• compatibility of disinfectants and sterilants
• nature of surface to be disinfected
• contact time
• temperature
• pH
• biofilms

Question 14

Critical items

Answer 14

-instruments or objects that are introduced directly into the bloodstream or into other normally sterile areas of the body

Question 15

Semicritical items

Answer 15

-noninvasive flexible and rigid fiber optic endoscopes, endotracheal tubes, anesthesia breathing circuits and cystoscopes

Question 16

Noncritical items

Answer 16

-those that either do not ordinarily touch the patient or touch only intact skin

Question 17

Are the Microbes Dead of Not?

Answer 17

-cide or cidal:
Killing of the microorganism
Germicides
-substances that kill microbes (pathogens and nonpathogens) but not necessarily their endoscopes
-bactericide
-fungicide
-virucide
-amoebicide
-static or stasis:
inhibit growth or multiplication of microorganism

Question 18

Relative Resistance of Viruses and Bacteria to the Action of Disinfectants

Answer 18

Low to High Resistance:
Lipid enveloped viruses (HIV, HBV)
Gram-positive bacterial (S. aureus, entercoccus)
Large non-enveloped virus (Adenovirus)
Fungi (Candida, Aspergillus)
Gram-negative bacteria (Pseudomonas)
Trophozoites (Acanthamoeba)
Small non-enveloped viruses (Polio virus)
Cysts (Giardia)
Spores (Bacillus, C. difficile)
Coccidia (Cryptosporidium)
Priors (CJD, BSE)

Question 19

Physical Methods of Microbial Control

Answer 19

Heat:

• incineration
• dry heat (hot air oven)- oil based
• moist heat- steam
• below 100 C- pasteurization
• at 100C- boiling
• above 100C autoclave

Radiation:

• UV radiation
• Ionizing radiation

Filtration

Question 20

Autoclaving

Answer 20

• steam under pressue
• 121C/15 psi for 15-90 mins
• 132C/27 psi for 4-20 mins
• minimal time required
• loading and packing critical to performance

Immediate Use (Flash) Sterilization

• the process of sterilizing unwrapped instruments using steam for 3 minutes at 270 F at 27-28 psi
• not used for routine sterilization- used in OR

Question 21

Pasteurization

Answer 21

• does not achieve sterility but kills pathogens that might be present in mill, dairy products and beer: Myocobacterium, Salmonella
• classic: 63C 30 min
• Flash HTST 72C 15 s, rapid cooling
• UHT (ultra high temp) 140C for 1s then rapid cooling

Question 22

Sterilization by Filtration

Answer 22

• excellent way to sterilize solution of heat-sensitive materials
• membrane filters (~0.1 mm thickness), Cellulose acetate, cellulose nitrate, polycarbonate, polyvinylidene, difluoride, other synthetic materials
• pore size 0.45 or 0.22 mm for bacteria
• 0.01 mm for spirochetes, mycoplasma, viruses and large proteins

-use N95 mask

Question 23

Radiation

Answer 23

• ionizing radiation: shorter wavelength
• ex: gamma rays, x-rays, high energy electron beams
• ionixation of water forms highly reactive hydroxyl radicals
• uses: pharmaceuticals, disposable dental and medical supplies (syringes, gloves, sutures)

Nonionizing radation:

• UV rays: thymine dimers inhibit replication of DNA
• use in rooms with TB can be airbourne
• not penetrating
• damage human eyes, skin cancer, burns

Question 24

Irradiated Blood Products and Food

Answer 24

• Irradiated RBC help to prevent graft versus host disease
• GVHD is a disorder where the grafted tissue attacks the host tissue by proliferation of T cells
• gamma radiation exposure prevents the proliferation of leukocytes especially T cells
• use of irradiation for food in the form of ionizing radiation destroys bacteria by damaging bacterial DNA
• prolongs the shelf-life of the food in cases where microbial spoilage is the limiting factor
• the treatment of hamburger eliminates the residual risk of a comtamination by E coli

Question 25

Phenol and Phenolics

Answer 25

• exert antimicrobial activity by injuring plasma membranes, inactivate enzymes and denaturing proteins
• phenol (carbolic acid) - irritates skin disagreeable odor is now rarely used
• used for intermediate and low level disinfection

Question 26

Hexachlorophene (pHisoHex)

Answer 26

• most active against gram positive bacteria
• toxic in newborns
• now used for staphylococcal skin decolonization in patients undergoing prosthetic or cardiac valve implant surgery

Question 27

Chlohexidine

Answer 27

• is not a phenol derivative
• frequently used for disinfection of skin and mucous membranes- ChloraPrep
• used for surgical hand scrubs and preoperative skin preparation of patients
• low toxicity. Strong affinity to skin or mucous membranes
• killing effect by damaging plasma membrane
• effective against most vegetative bacteria but not sporicidal
• Disadvantages: genes conferring resistance observed in bacteria; allergies observed

Question 28

Aldehydes

Answer 28

• work by forming covalent crosslinks with a number of organic functional groups on proteins
• formalin: 37% aqueous solution of formaldehyde gas
• glutaraldehyde: used to sterilize hospital instruments
• less irritating more effective than formaldehyde
• Cidex (2% soln): bactericidal, tuberculocida, virucidal in 10 min; sporicidal in 3 to 10 hr
• is the only liquid chemical disinfectant that can be considered a sterilant

Question 29

Gaseous Chemosterilizers

Answer 29

• ethylene oxide, propylene oxide
• denaturation of proteins by alkylation
• sterilize without heat
• sterilization of medical supplies and equipment: disposable plastic syringes, lensed instruments, artificial heart valves, heart-lung machine and mattresses
• Note: formaldehyde gas rarely used
• ETO is toxic, a carcinogen and flammable; requires aeration time to remove ETO residue

Question 30

Quaternary Ammonium Compounds

Answer 30

Advantages:

• combined detergent and germicidal activity
• stable and working dilutions have low toxicity

Disadvantages:

• non sporicidal, limited activity against viruses, mycobaceria
• may support growth of bacteria

Uses:

• surface decontamination- floor and walls
• equipment wipe down
• antiseptic formulations availible

Quarternary Ammonium Compounds- Topical uses

• Benzalkonium chloride: Zephiran (antisepsis of skin and mucous membranes and as a disinfectant)
• Cetylpyridinium chloride: Cepacol/ Colgate Total

Question 31

Alcohols

Answer 31

• dehydrate cells, disrupt membranes and cause coagulation of protein
• may be used for hard surface disinfection or skin antisepsis
• types: Isopropyl alcohol and methyl alcohol and ethyl alcohol
• a 70% aqueous solution is more effective at killing microbes than absolute alcohols

uses:

• skin disinfectant (antiseptic)
• surface decontamination
• benchtop, cabinet wipedown

Advantage: good for intermediate and low level disinfection, inactivate most viruses with a lipid envelope

Disadvantage: cannot penetrate protein-rich materials, flammable

Question 32

Handwashing

Answer 32

• single most important procedure for preventing nosocomial infections
• defined as a vigorous, brief rubbing together of all surfaces, followed by rinsing under a stream of water
• although various products are available, handwashing can be classified simply by whether plain soap or detergents
• hand sanitizers

Question 33

Halogens: Iodine and Chlorine

Answer 33

• they are oxidizing agents and cause damage by oxidation of essential sulfydryl groups of enzymes
• chlorine reacts with water to form hypochlorous acid, which is microbicidal
• chlorine gas is used to bleach water
• household bleach can be used at a dilution of 1:10 in decontamination of spillage of infectious material
• disadvantage: unstable when diluted- needs to be made daily

Question 34

Iodine Preparations

Answer 34

• tincture of iodine (2% iodine in 70% alcohol) is an antiseptic
• iodophore: iodine can be combined with neutral carrier polymers such as polyvinylpyrrolidone to prepare iodophores such as povidone-iodine
• iodophores permit slow release and reduce the irritation of the antiseptic
• Betadine, Isodine

Disadvantage: cannot be used to disinfect medical equipment unless at higher concentrations; commercial preparations are not sporicidal at the dilutions recommended for use

Question 35

Heavy Metals and Organic Acids

Answer 35

• metal ions combine with SH groups on proteins
• heavy metals: silver nitrate (1% for ophthalmic preparations); merchurochrome (mercury); copper sulfate; zinc chloride; zinc oxide
• organic acids and derivatives- sorbic acid; benzoic acid; methylparaben; propylparaben

Question 36

Hydrogen Peroxide

Answer 36

• acts on the microorgnisms through its release of nascent oxygen. Hydrogen peroxide produces hydroxyl-free radical that damages proteins and DNA
• used at 6% concentration to decontaminate instruments and equipment such as ventilators
• 3% Hydrogen Peroxide Solution is used for skin disinfection and cleaning of wounds and ulcers
• strong solutions are sporicidal
• disadvantages: decomposes in light, broke down by catalase, proteinaceous organic matter drastically reduces its activity

Question 37

Peracetic Acid

Answer 37

• a mixture of acetic acid and hydrogen peroxide in an aqueous solution
• PAA disinfects by oxidizing of the outer cell membrane of vegetative bacterial cells, endospores, yeast and mold spores

Uses:

• peracetic acid can be used as a cooling tower water disinfect where it prevents bio film formation and effectively controls Legionella bacteria
• peracetic acid is extremely effective for sanitizing fowl carcasses without affecting the skin or the flesh of the bird by applying direct to the meat
• plasma (gas phase) sterilization

Question 38

Plasma sterilization

Answer 38

• beneficial for sterilizing temperature sensitive polymeric material-such as endoscopes
• provides safe non-toxic dry, low temp sterilization in about 1 hr
• gas plasma is generated in an enclosed chamber under deep vacuum using UV or microwaves to create free radical in a gaseous phase

Vacuum applied -> H2O2 or PAA injected which beomces gas -> UV/MW applied free radicals formed -> bacteria killed -> activated radicals lose energy and form water

Question 39

STERRAD Sterilization System

Answer 39

• uses low temperature, hydrogen peroxide gas plasma technology to sterilize instruments and medical devices
• quick instrument reprocessing
• express cycle for da Vinci 3;D endoscopes and other devices without lumens
• processes a wide range of instruments including multiple single-channel flexible endoscopes, cameras, rigid scopes, light cords, batteries, and power drills