2. Contents
⢠Historical background
⢠Introduction
⢠Factors Affecting Disinfection
⢠Types of disinfection
⢠Methods Of Disinfection & Sterilization
â Natural Methods
â Physical Methods
â Chemical Methods
⢠Some practical aspects
⢠CSSD
⢠References
3. Historical background
⢠The scientific use of disinfection and
sterilization methods originated more than 100
years ago.
⢠Ignatz Semmelweis(1816-1865) and Joseph
Lister(1827-1912) -important pioneers for the
promotion of infection control.
4. Historical background
⢠More than 100 years ago, Semmelweis
demonstrated that routine hand washing can
prevent the spread of disease.
⢠He worked in a hospital in Vienna where
maternity patients were dying at an alarming
rate.
⢠He recognized that medical students worked
on cadavers during an anatomy class and
afterwards they went to the maternity ward.
5. Historical background
⢠Students did not wash their hands between
touching the dead and the living!!!
⢠After administrating the hand washing before
examining the maternity patients the mortality
rate decreased.
6. Historical background
⢠Lister, for the first time, used carbolic
acid in operating theatres that significantly
reduced mortality rates.
⢠In 1867, Lister introduced the use of phenol as
antimicrobial agent for surgical wound
dressings.
⢠His principles were gradually adopted in
Britain and later in US.
⢠This was the beginning of infection control.
7. Introduction
Sterilization-
⢠Destruction of all forms of life, including the
bacterial spores, viruses, prions
⢠No degrees of sterilization: an all-or-nothing
process.
⢠Physical or chemical methods.
8. Introduction
Disinfection -
⢠Less lethal than sterilization. Destroys most
recognized pathogenic organisms but not
necessarily all microbes (e.g. Spores)
⢠Purpose-prevent transmission of certain
microorganisms with objects, hands or skin
and prevent spreading the infection.
⢠Physical or chemical methods.
9. Introduction
⢠Disinfectant â usually a chemical agent that
destroys disease causing pathogens or other
harmful microorganisms, but might not kill
bacterial spores. Refers to substances applied
to inanimate objects.
⢠Antiseptic â Substance that prevents or arrests
the growth of microorganisms. Preparations
applied topically to living tissues.
10. Introduction
⢠Asepsis- prevention of contact with
microorganisms.
⢠Sanitizer â Agent that reduces the number of
bacterial contaminants to safe levels.
⢠Sterile â State of being free from all
microorganisms.
11. Introduction
⢠Detergent â Surface cleaning agent that makes
no antimicrobial claims. Acts by lowering
surface tension.
⢠Cleaning â Removal of adherent visible soil,
blood , and other debris from surfaces ,
crevices , serrations and lumens of
instruments.
12. Factors that influence the degree of
killing
⢠Types of organisms
⢠Number of organisms
⢠Concentration of disinfecting agent
⢠Presence of organic material (e.g., serum, blood)
⢠Nature (composition) of surface to be disinfected
⢠Contact time
⢠Temperature
⢠pH
⢠Biofilms
⢠Compatibility of disinfectants and sterilants
13. Factors that influence the degree of
killing
Type of organisms
⢠Organisms vary in their ability to withstand
chemical and physical treatment, e.g.,
⢠Sporesâhave coats rich in proteins, lipids and
carbohydrates
⢠Mycobacteriaâcell walls are rich in lipids
⢠Prionsâthe most resistant known organisms to
the action of heat, chemicals, and radiation !!!
15. Factors that influence the degree of
killing
Number of organisms
⢠Microbial load-the total number of organisms
which determine the exposure time of killing
agent
⢠organisms have varying degrees of susceptibility
to killing agents
⢠not all organisms die at the same time
⢠the death curve is logarithmic!!!
⢠higher numbers of organisms require longer
exposure.
17. Factors that influence the degree of
killing
Concentration of disinfecting agent
⢠a proper concentration of disinfecting agents
ensure the killing of target organisms, e.g.,
⢠povidone-iodine should be diluted with water
before use because there is not enough free
iodine to kill microorganisms in concentrated
solution.
18. Factors that influence the degree of
killing
⢠Presence of organic material(such as blood,
mucus, pus) affects killing activity by
inactivating the disinfecting agent, e.g,
⢠by coating the surface to be treated, prevents
full contact between object and agent
(Glutaraldehyde)
⢠For optimal killing activity, instruments and
surfaces should be cleansed of excess organic
material before disinfection !!!
19. Factors that influence the degree of
killing
⢠Nature (composition) of surface to be
disinfected
⢠some medical instruments are manufactured of
biomaterials that exclude the use of certain
disinfection and sterilization methods because
of possible damage, e.g.,
⢠endoscopic instruments cannot be sterilized by
the heat in an autoclave.
20. Factors that influence the degree of
killing
Contact time
⢠the amount of time a disinfectant or sterilant is in
contact with the object is critical e.g.,
⢠Betadine must be in contact with object for at
least 1 to 2 min to kill microbes.
⢠the spores of bacteria and fungi need a much
longer time
⢠determine whether it is disinfecting or sterilizing
the object.
21. Factors that influence the degree of
killing
Biofilms
⢠communities of microorganisms.
⢠can be on a surface of either inanimate or
animate objects, e.g, catheters , pipes that carry
water.
⢠make disinfection more difficult.
⢠the concentration of the disinfectant and the
contact time need to be increased.
22. Factors that influence the degree of
killing
Compatibility of disinfectants
⢠a common mistake is to believe that two
disinfectants are better than one !
⢠some of them may inactivate other, e.g.,
⢠the bleach and quaternary ammonium
compound together negate the activity of both.
23. Ideal disinfectant
⢠Highly efficacious
⢠Fast
⢠Good penetration
⢠Compatible with most materials
⢠Non-toxic
⢠Effective despite presence of organic material.
⢠Residual effect
⢠Economical
⢠Odourless
24. Types of disinfection
⢠Concurrent disinfection â
â Application of disinfective measures as soon as
possible after the discharge of infectious material
from the body of an infectious person.
â Consists of disinfection of urine ,faeces , vomit,
clothes ,hands ,dressings, apron ,gloves.
⢠Terminal disinfection -
â Application of disinfective measures after the
patient has died or has ceased to be a source of
infection.
25. Types of disinfection
⢠Precurrent (prophylactic) disinfection â
Disinfection of water by chlorine ,
pasteurization of milk ,hand washing.
26. Types of disinfectants
High-level disinfectants
⢠activity against bacterial spores
Intermediate-level disinfectants
⢠tuberculocidal activity but not sporocidal
Low-level disinfectants
⢠a wide range of activity against
microorganisms but no sporocidal or
tuberculocidal activity
27. Types of materials in healthcare
Critical materials
⢠invade sterile tissues or enter the vascular
system.
⢠most likely to produce infection if
contaminated and therefore require
sterilization.
⢠E.g. Surgical instruments , cardiac catheters
28. Types of materials in healthcare
Semicriticial materials
⢠have contact with mucous membranes
⢠require high-level disinfection agents
⢠E.g.cystoscope ,laryngoscope blade.
Noncriticial materials
⢠have contact with intact skin
⢠require intermediate-level to low-level
disinfection
⢠E.g. bedpans , BP Cuffs
30. Natural agents
⢠Sunlight â
â UV rays of sunlight lethal to bacteria and some
viruses.
â Articles such as linen, bedding and furniture may
be disinfected.
⢠Air
â Acts by drying or evaporation of moisture which is
lethal to most bacteria.
31. Physical agents
⢠Burning
â Inexpensive articles such as contaminated
dressings , rags and swabs â disposed off by
burning.
â Best done in an incinerator.
â Addition of sawdust, paper ,kerosene or other
combustible material aid in burning.
32. Physical agents
⢠Hot air
â Articles such as glassware
,syringes , swabs , dressings
and sharp instruments.
â Drawback â no penetrating
power: not suitable for bulky
materials.
â Hot air oven â temp 160-180
deg C for at least 1hour to kill
spores.Hot air oven
33. Physical agents
⢠Thermal Death Point (TDP): Lowest
temperature at which all of the microbes in a
liquid suspension will be killed in ten minutes.
⢠Thermal Death Time (TDT): Minimal length of
time in which all bacteria will be killed at a given
temperature.
⢠Decimal Reduction Time (DRT): Time in
minutes at which 90% of bacteria at a given
temperature will be killed. Used in canning
industry.
34. Physical agents
MOIST HEAT
⢠Kills by denaturing proteins and destroying
cytoplasmic membranes.
⢠More effective than dry heat; water better
conductor of heat than air.
⢠Methods of microbial control using moist heat
â Boiling
â Autoclaving
â Pasteurization
35. Physical agents
⢠Boiling
â for 5-10 minutes :kill bacteria but not spores or
viruses.
â Temp. above 100 deg C required for destruction of
spores.
â Disinfection of small instruments , tools not used
for subcutaneous insertion , linen and rubber
goods such as gloves.
â Slow process , unsuitable for thick beddings and it
fixes albuminous stains.
36. Physical agents
⢠Autoclaving
âOperate at high temperature and pressure.
âDestroys all forms of life , including spores.
âSterilization of linen , dressings , gloves ,
syringes , instruments and culture media.
âNot suitable for plastics and sharp
instruments.
38. Physical agents
Pasteurization
⢠A process in which fluids are heated at
temperatures below boiling point to kill
pathogenic microorganisms in the vegetative
state without altering the fluidâs palatability.
⢠Conditions: 62â, 30min or 71.7â, 15sec
⢠Significance: kills vegetative pathogens.
40. Physical agents
⢠Radiation
âSterilization of bandages , dressings , catgut
and surgical instruments.
âGreat penetrating power with little or no
heating effect.
âMost effective ,but very costly.
âNormally carried out by gamma radiation.
41. Physical agents
⢠Filtration: Removal of microbes by passage of a
liquid or gas through a screen like material with
small pores. Used to sterilize heat sensitive
materials like vaccines, enzymes, antibiotics, and
some culture media.
⢠0.22 and 0.45um Pores: Used to filter most
bacteria. Donât retain spirochetes, mycoplasma
and viruses.
⢠0.01 um Pores: Retain all viruses and some large
proteins
42. Chemical agents
Phenol and related compounds
⢠Intermediate- to low-level disinfectants
⢠Denature proteins and disrupt cell membranes
⢠Effective in presence of organic matter and
remain active for prolonged time.
⢠Commonly used in health care settings, labs, and
homes (Lysol, triclosan)
⢠Have disagreeable odor and possible side effects.
43. Chemical agents
⢠Phenol(carbolic acid) â not an effective
disinfectant
⢠Crude phenol- phenol and cresol. effective
against gram +ve and âve organisms.
⢠Cresol â used in 5 to10 % for disinfection of
urine and faeces.
⢠Cresol emulsions â very powerful
disinfectants
44. Chemical agents
⢠Chlorhexidine (hibitane ) â most useful skin
antiseptic. 0.5% solution used as
handlotion.1% creams used for burns
⢠Hexachlorphane â slow in action , but shows
cumulative effect on skin and is compatible
with soaps.
⢠Dettol (chloroxylenol) â relatively non toxic
antiseptic.5 % dettol for disinfection of
instruments and plastic equipments.
45. Chemical agents
Quaternary ammonium compounds
â Cetrimide(cetavlon)
â bactericidal against vegetative gram +ve
organisms , much less against gram -ve
â Used in 1-2 % strength
â Savlon
â Combination of cetavlon and hibitane .
â Plastic appliances may be disinfected in 20 min.
â Disinfection of clinical thermometers in 3 minutes.
46. Chemical agents
Halogens and their compounds
⢠Intermediate-level antimicrobial chemicals
⢠Believed that they damage enzymes via oxidation
or by denaturing them.
⢠Iodine tablets, iodophores (BetadineŽ), chlorine
treatment of drinking water, bleach, chloramines
in wound dressings, and bromine disinfection of
hot tubs.
47. Chemical agents
Alcohols
⢠Intermediate-level disinfectants.
⢠Denature proteins and disrupt cytoplasmic
membranes.
⢠Evaporate rapidly.
⢠Swabbing of skin with 70% ethanol prior to
injection.
48. Chemical agents
Isopropyl Alcohol (70%)
⢠Powerful disinfectant and antiseptic
⢠Mode of action: denatures proteins, dissolves
lipids and can lead to cell membrane
disintegration
⢠Effectively kills bacteria and fungi
⢠But does not inactivate spores!
49. Chemical agents
Aldehydes
⢠Denature proteins and inactivate nucleic
acids.
⢠Glutaraldehyde both disinfects (short
exposure) and sterilizes (long exposure)
⢠Formalin used in embalming and disinfection
of rooms and instruments.
50. Chemical agents
Formaldehyde
âHighly toxic and irritant gas
âEffective against vegetative bacteria ,fungi
and many viruses.
âUsed as a 2-3 % solution for spraying rooms
, walls and furniture
âMost effective at a high temperature and
relative humidity of 80-90%
51. Chemical agents
Oxidizing agents
⢠Peroxides, ozone, and per acetic
acid kill by oxidation of microbial enzymes
⢠High-level disinfectants and antiseptics
⢠Hydrogen peroxide can disinfect and sterilize
surfaces of objects.
⢠Ozone -treatment of drinking water.
⢠Per acetic acid â effective sporocide used to
sterilize equipment.
52. Chemical agents
Surfactants
⢠Surface active chemicals that reduce surface
tension of solvents to make them more effective
at dissolving solutes
⢠Soaps and detergents
⢠Colorless, tasteless, harmless to humans, and
antimicrobial; ideal for many medical and
industrial uses.
⢠Low-level disinfectants.
53. Chemical agents
Metals-
⢠Ions are antimicrobial because they alter the 3-D
shape of proteins, inhibiting or eliminating their
function.
⢠Low-level bacteriostatic and fungistatic agents.
⢠1% silver nitrate to prevent blindness caused by
N. gonorrhoeae .
⢠Thiomersal (mercury-containing compound) used
to preserve vaccines.
54. Chemical agents
Lime
âCheapest disinfectant
âUsed as fresh quick lime or 10-20 %
aqueous suspension known as milk of lime.
âFaeces and urine disinfected by 10-20%
aqueous solution (in 2 hrs).
âUsed as a deodorant in public places where
toilets are located.
55. Chemical agents
Ethylene oxide
â for heat sensitive articles
â At 55- 60 deg C : kills bacteria ,spores and viruses.
â Mixed with 12 % carbon dioxide (as it is
explosive)
â Water vapor added to the mixture to increase
efficacy.
â To sterilize fabrics, plastic equipment , cardiac
catheters , etc.
56. Some Newer agents
⢠BacillocidŽ rasant
â Formaldehyde-free disinfectant cleaner with low
use concentration
⢠Virkon
â gaining importance as non Aldehyde compound
â Disinfects medical devices and lab equipments.
â Decontaminate spillages with Blood and body
fluids.
57. Gas plasma sterilization
⢠Gas plasma generated in an enclosed chamber
under deep vacuum using Radio frequency or
Microwave.
⢠Can be used for hand sterilization.
⢠The mechanism of action of this device is the
production of free radicals within a plasma
field that are capable of interacting with
essential cell components
58. Sterilization Control
⢠To ensure that potentially infectious agents are
destroyed by adequate sterilization regimes
⢠Three levels:
⢠physical: measuring device control (temp.,
time, pressure)
⢠Biological
⢠Chemical
59. Sterilization Control
Biological:
⢠Bacillus stearothermophilus spores(104-106
organisms)
⢠survives steam heat at 121ºC for 5 min. and is
killed at 121ÂşC in 13 min.
⢠validate and determine the adequacy of steam or
chemical sterilization.
⢠Bacillus subtilis/B.atrophaeus spores
⢠validate and determine the adequacy of ethylene
oxide or dry heat sterilization.
60. CHEMICAL INDICATORS
⢠Browne's tubes are glass tubes that contain
heat sensitive dyes. These change color after
sufficient time at the desired temperature.
⢠Before heat exposure, the contents of the tube
appear red.
⢠As heating progresses, the color changes to
green.
61. CHEMICAL INDICATORS
â˘Bowie Dick tape
is applied to
articles being
autoclaved. Before
heat exposure, the
tape is uniformly
buff in color.
â˘After adequate
heating, the tape
develops dark
brown stripes.
The pack on the left has been properly
sterilized; that on the right has not.
62. SOME PRACTICAL ASPECTS
Disinfection of faeces & urine-
⢠Collected in impervious container.
⢠Add equal volume of disinfectant for 1-2 hrs.
Disinfectant Amount per litre Percent
Bleaching
powder
50 gms 5
Crude phenol 100ml 10
Cresol 50 ml 5
Formalin 100 ml 10
63. Disinfection of faeces & urine-
⢠Quick lime or milk of lime can be used if
above disinfectants not available.
⢠Bedpans and urinals â steam disinfected.
64. Disinfection of sputum
⢠Received in gauze or paper handkerchief .
⢠Destroyed by burning.
⢠Disinfected by boiling or autoclaving for 20
min at 20 lbs pressure.
⢠Or 5 % cresol can be used.
65. ⢠Disinfection of blood/body fluids spills
â Clean the affected area with soap and water then
disinfect with a 1%Na hypochlorite solution for 15
minutes.
⢠HIV infected articles
â Cleaning and 2% glutaraldehyde for 30 minutes.
â 6% Hydrogen peroxide for 30 minutes.
â 1% hypochlorite solution for 30 minutes.
66. Fumigation
⢠To sterilize the operation theatre formaldehyde
gas (bactericidal & sporicidal, viricidal) is
widely employed as it is cheaper for
sterilization of huge areas like operation
theatres.
⢠Formaldehyde is irritant to eye & nose; and it
has been recognized as a potential carcinogen.
67. References
⢠K.Park Textbook of Preventive and Social
medicine 23rd edition.
⢠CDC â Sterilization and disinfection
guidelines
⢠Hospital hygiene and infection control âWHO.
⢠WHO Pharmacoepia Library- Methods of
Sterilization.
⢠Occupation Safety and Health administration-
Disinfection guidelines.