Download ii. infection control

CHAPTER 3
Sterilization, Disinfection and Infection Control
From the time of debates about the germ theory of disease, killing microbes before they
reach patients has been a major strategy for preventing infection. Understanding how
they work is of increasing importance in an environment that includes
immunocompromised patients, transplantation, indwelling devices, and acquired
immunodeficiency syndrome.
DEFINITIONS
1. Sterilization is complete killing, or removal, of all living organisms from a
particular location or material. Spores are particularly resistant
2. Pasteurization is the use of heat at a temperature sufficient to inactivate
important pathogenic organisms in liquids such as water or milk but at a
temperature below that needed to ensure sterilization.
3. Disinfection is the destruction of pathogenic microorganisms by usually
chemical processes that fail to meet the criteria for sterilization.
4. Antiseptics are disinfectant agents that can be used on body surfaces
5. Sanitization is a less precise term with a meaning somewhere between
disinfection and cleanliness
6. Asepsis describes processes designed to prevent microorganisms from reaching
a protected environment. It applies sterilization and disinfection to create a
protective environment
MICROBIAL KILLING
1. Bacterial killing follows exponential kinetics
2. Achieving sterility is a matter of probability
3. Heterogeneous microbial subpopulations may extend the killing kinetics
I. STERILIZATION
A. Heat
1. Incineration is rapid and effective
2. Dry heat requires 160°C for 2 hours to kill all forms including spores
3. Moist heat is more effective and allows for rapid denaturation of protein
4. Boiling water fails to kill bacterial spores
5. Autoclave creates 121oC of steam under pressure for 15 min.
6. Steam displaces air from the autoclave
7. Killing rate increases logarithmically with arithmetic increase in temperature
8. Condensation and latent heat increase effectiveness of autoclave
9. Access of pure saturated steam is required for sterilization
10. Impermeable or large volume materials present special problems
11. Flash autoclaves use 134°C for 3 minutes
B. Gas
1. Ethylene oxide sterilization is used for heat-labile materials
2. Aeration needed after ethylene oxide sterilization
3. Formaldehyde and oxidizing agents are useful in sterilization
C. Ultraviolet Light and Ionizing Radiation
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2.
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4.
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UV light causes direct damage to DNA
Use of UV light is limited by penetration and safety
Ionizing radiation damages DNA
Use for surgical supplies, food
Killed organisms may remain morphologically intact and stainable
II. DISINFECTION
A. Physical Methods
a. Filtration
1. Membrane filters remove bacteria by mechanical and electrostatic mechanisms
2. Used for disinfection of fluids, especially those containing heat-labile components
b. Pasteurization
1. Exposure of liquids to temperatures in the range 55 to 75°C equipment free of
organisms that may otherwise multiply in mucus and humidifying water.
2. Kills vegetative bacteria but not spores
3. Used for foods and fragile medical equipment
c. Microwaves
1. Microwaves kill by generating near boiling heat
B. Chemical Methods
1. Most agents are general protoplasmic poisons
2. Disinfectants are variably inactivated by organic material
3. Activity against spores and viruses varies
a. Alcohol
1. Alcohols require water for maximum effectiveness
2. Action of 70 to 95% alcohol is slow
3. Inactive against bacterial spores and many viruses
b. Halogens
1. Iodine acts by iodinating or oxidizing essential components of the microbial
cell
2. Tincture of iodine in alcohol is effective
3. Iodophors combine iodine with detergents
4. Chlorine oxidative action is rapid but activity is reduced by organic matter
5. 5% chlorine solution is called hypochlorite.
6. Legionella may resist chlorine action
c. Hydrogen Peroxide
1. Hydrogen peroxide oxidizes cell components
d. Surface-Active Compounds
1. Hydrophobic and hydrophilic groups of surfactants act on lipids of bacterial
membranes
2. Quaternary ammonium compounds (Quats) such as benzalkonium chloride are
bactericidal in the absence of contaminating organic matter.
3. Little activity against viruses
4. Quats adsorbed to surfaces may become contaminated with bacteria
5. Cationic detergents are neutralized by soaps
e. Phenolics
1. Phenol is a potent protein denaturant and bactericidal agent.
2. Relatively stable to protein
3. Environmental contamination with phenols and cresols limits use
4. Skin binding of hexachlorophene enhances effectiveness for staphylococci but
absorption through skin limits use
5. Chlorhexidine also binds to skin but is less toxic
f. Glutaraldehyde and Formaldehyde
1. Glutaraldehyde and formaldehyde are alkylating agents highly lethal to essentially
all microorganisms
2. Glutaraldehyde is useful for decontamination of equipment
Infection Control and Nosocomial Infections
I. NOSOCOMIAL INFECTIONS AND THEIR SOURCES
1.
2.
3.
4.
5.
Infections during hospitalization are either community acquired or nosocomial.
Community infections are those acquired before admission
Nosocomial infections are those acquired in hospital
Endogenous infections are part of hospital risk
Hospital sources other than the patient include hospital personnel, the
environment, and medical equipment.
A. Hospital Personnel
1. Cross-infection is usually by direct contact
2. Infected medical attendants are particularly dangerous
3. Infection from carriers can transmit to patients
B. Environment
1. Airborne environmental contamination is relatively unimportant
2. M. tuberculosis and Legionella are risks
C. Medical Devices
1. Equipment that crosses epithelial barriers provides microbial access
2. Conditions for bacterial growth (water, nutrients) increase risk
3. Transcutaneous and indwelling devices should be changed as frequently as
possible
a. Urinary Catheters
1. Urinary tract infection accounts for 40 to 50% of all nosocomial infections, and at
least 80% of these are associated with catheterization.
2. Closed urinary drainage systems are still violated
b. Vascular Catheters
1. Needles and catheters placed in veins or arteries for fluid administration or
diagnostic monitoring are a leading cause of nosocomial bacteremia.
2. Skin is the primary source for intravenous contamination
c. Respirators
1. Machines that assist respiration have a potential for nosocomial pneumonia if the
aerosol they deliver becomes contaminated
2. Bacterial growth occurs in the parts of the system that contain water
3. Changing tubing etc. controls nebulizer contamination
D. Blood and Blood Products
1. Risk generally greater for health care workers rather than patients.
2. Hepatitis B, hepatitis C, and HIV risk is related to blood manipulation
3. Screening is determined by institutional policy
II. INFECTION CONTROL
1. Antisepsis attacks contaminating organisms
2. Asepsis prevents contamination from reaching vulnerable sites
A. Asepsis
a. Operating Room
1. Sterile drapes and instruments prevent contact of organisms with wound
2. Airborne bacteria are associated with personnel in operating room
b. Hospital Ward
1. Asepsis is practiced by the use of sterile needles, medications, and dressings
2. Invasive procedures such as catheter insertion and lumbar puncture are performed
under aseptic conditions
3. Handwashing is the most important preventive measure
c. Outpatient Clinic
1. Practices used on the hospital ward are used
2. Waiting areas present a risk
B. Isolation Procedures
1. Isolation places barriers between the infected patient and others
2. Standard precautions include the use of gowns and gloves when in contact with
patient blood or secretions.
3. Application to all patients protects health care workers from HIV
4. Transmission precautions block airborne, droplet, and contact routes
5. The use of surgical masks, specially designed respirators, and control of room air
circulation block transmission
C. Organization
1. Modern hospitals have formal infection control programs that include an infection
control committee, epidemiology service, and educational activities.
2. Infection control committees determine and enforce policy
3. Epidemiologic surveillance and outbreak investigation are required
4. On-the-spot investigation of potential outbreaks allows early implementation of
preventive measures