sterilization and disinfection

1. Sterilization &
Disinfection
Dr.Ghada AbdelWahed Ismail
Professor of Clinical Pathology
Head of Central Infection Control Unit
Ain Shams University Hospitals

2. Intended learning objectives:
1-Define sterilization & sterile object.
2-Define sterility assurance level (SAL).
3-Differentiate between decontamination,
cleaning, sterilization & disinfection.
4-Identify methods of decontamination&
cleaning.
5-Enumerate methods of packing.
6- List methods of sterilization.
7-List steps of sterilization process.

3. 8-Enumerate different methods of
sterilization.
9-Enumerate different types & conditions
of sterilizers.
10-Compare between low temerature
sterilizers.
11-Define disinfection & it’s indication.
12-Enumerate different methods of
disinfection & their conditions.
13-List levels & steps of disinfection.

4. Killing all of micro-organisms,
including spores.
The absence of all viable
organisms including viruses
and spores

5. But:
Whatever long you apply the
sterilizing agent there will be
always a fraction that will survive;
the number becomes very small,
but will never reach zero.
Absolute sterility cannot be
achieved.

6. • Research shows that the number of micro-
organisms that are killed each minute (or
other unit of time) of exposure to the
sterilizing agent is a constant percentage
of the number of living micro-
organisms at the beginning of each
minute.
i.e when a population of one type of
micro-organisms is exposed to a killing
agent, not all will die at the same time.

8. A medical device is considered
sterile if the chance that there are
viable micro-organisms on the product
is less than 1 to a million i-e 10-6

9. Sterilization can not be
achieved unless the device is
clean.
So there is a chain of processes
starting immediately after using
medical devices.
Each Step is necessary

10. Used
medical device
wards / O.R.
Storage
Control Sterilization
Conditioning
(packing)
Cleaning
Decontamination

11. Definition: it is a method whereby an object or material
(surgical instruments or bed linens) is freed of the
contaminating agent.
Objectives:
 To lower Bioburden on the device.
 To prevent drying of blood & secretions facilitate
cleaning.
 To protect staff when handling instruments.
 To avoid environmental contamination.
Method:
- Chemical: Soaking in a detergent.
- Thermal : 90 ْ ◌
C > 1 min.
80 ْ ◌
C > 3 min.

12. i-e Physical removal of dirt, and
organic material from the medical
device by flushing away in the
presence of a detergent.
 It is obligatory before any
disinfection or sterilization process.
 Same detergent used in the
decontamination.

13. Methods:
A) Manual.
b) Automatic machines :
• Washer disinfectors
• Ultrasonic cleaner
Inspection :
 No Stain  No Dirt
 No Rust  Functionality of the instrument

14. Manual cleaning
• Done with cold water to avoid
denaturation & coaguation of proteins
of blood or sputum that make it
difficult to remove.
• Use PPE.
• Done under water to avoid spread of
aerosol.
• Open locks of instruments & use
brush.

16. • Objectives:
To protect sterile equipments.
To prevent recontamination before sterilization.
• Method using:
A-Disposable paper sheets
, complying with standard
porosity and resistance.
B- Bags.
C-Containers.

17. Moist heat (121 - 138 ْ ◌C)
• Heat
Dry heat (160 - 180 ْ ◌C (250 ْ ◌C)
Ethylene oxide (32 - 55 ْ ◌C)
• Gas
Low temperature steam
Formaldehyde (56 - 80 ْ ◌C)
γRays (Ambient)
• Radiations
Electron beam (Ambient)
• Plasma Associated with hydrogen peroxide
(sterrad) (45 ْ ◌c)
Peracetic acid
(Plazlyte) (45 ْ ◌c)

18. • Introduction:
• Steam is very effective in transferring
heat that can kill micro-organisms at
relatively low temperatures in a short
time.
• To reach such high temperature the
steam needs to be pressurized.
• Advantage Of Steam:
* Can be made quite easily. SAL 10-60
* Clean - not toxic - not corrosive.

19. Sterilization Process with
Fractionated pre-vacuum.
1) Air removal 2) Pressure build-up / Heating up
3) Sterilization 4) Steam release
5) Drying 6) Air admission

20. 1) Heating up of water and air removal by
fractionated:
It is an extremely critical phase.
In this process, a vacuum is drawn
and then a pulse of steam is admitted.
The pressure of the pulse could be
below or just above the atmospheric
pressure.

21. Both air & steam present in the chamber will
be withdrawn & new pulse is admitted.
The air fraction inside the chamber become
smaller.
So the fractionated pre-vacuum process is the
most safe sterilization process for all
materials in which air can be trapped.
At the end of this step the chamber will be
filled with the saturated steam (best
penetration power)

22. Effect of Steam Pulsing
With each pulse the steam
penetrates deeper & deeper

23. • Air removal by gravity displacement:
There is no guarantee for complete air
removal.
So the steam will be mixed with air
unsaturated steam Low
penetration power less effective

24. 2) Building up of pressure:
The vessel is sealed & the temperature and
pressure increase to the required level.
3) Sterilization time (Holding time).
Temperature Pressure Holding time
121 ْ ◌C 1.0 bar 20 min
125 ْ ◌C 1.3 bar 10 - 15 min
134 ْ ◌C 2.05 – 2.04 bar 3 , 3.5 , 4 , 10 ….18

25. Holding Time:
134 ْ ◌
C - 138 ْ ◌
C : 3.5 min Bowie Dick test.
5-10 min according to the load
& the quality of the
autoclave.
18 min Creutzfeldt- jakob
disease
125 ْ ◌
C : 15 – 20 min for textiles.
121 ْ ◌
C : 20 min for plastic &
caoutchouk
1 min at 134 ْ ◌
C is equivalent to 20 min at 121 ْ ◌
C
1 min at 125 ْ ◌
C is equivalent to 2.5 min at 121 ْ ◌
C

26. 4) Reducing the pressure to atmospheric
by releasing the steam.
5) Cooling down of the load & drying by
vaccum
N.B wet equipment is not sterile.

27. Control to be operated
• Chart record (T ْ ◌
/P ْ ◌
)
• Bowie-Dick test
• Chart record (T ْ ◌time)
• Temperature sensor
• Bowie-Dick test
• Chemical indicators
(Multiparameter)
Steam characteristic
• Saturated
• Able to kill
• Able to penetrate into
the deptht of the items

28. Phase of the cycle
• Air removal
• Holding time
• Steam release & drying
Control to be operated
• Bowie-Dick test
• Chart record
• Chart record
• Temperature sensors
• Chemical indicators
(Multi variable parameter)
• Chart record
• Dryness
• Chemical indicators
(single variable parameter)

29. Bowei Dick Test

30. Control of sterilization process
* Log BOOK.
* Physical control:
1. Leak test
2. B.D. Steam penetration & distribution.
3.Chart record time, temperature,
pressure.
* Chemical indicator: strips.
* Physico.chemical indicator.
* Biological indicators ???

31. Types of Small Steam
Sterilizers (< 54 liters)
I. Real Sterilizers * for double wrapped solids,
(type B/EN 13 060-2) hollow instrument, & porous
products.
* vacuum pump or venturi
system.
* air removal obtained by
vacuum and sub / super
atmospheric pulses.

32. Real Sterilizers * Long cycle (40-55min)
(type B/EN 13 060-2) at the end of the cycle
dry load.
Wrapped goods can be
stored for use later.
* price + + +

33. II. Steam Disinfectors * for non wrapped solid
products.
(type N/EN 13 060-3) * air is removed partially by
(Flash sterilizer) gravity displacement
! (valve), no pulses.
* no drying stage.
* short cycle (13-20 min)
* price + to + +

34. III. Sterilizers intended * for non wrapped solid
products,
for the sterilization and either porous loads or
of products specified hollow products, single
by the manufacturer wrapped product OR multi
(type S/EN 13 060-4) wrapped products &/or
drying stage.
* gravity displacement or
pulses.
* price + + to + + +

35. Applications of use
of small sterilizers
1) Type (B) (Vacuum assisted): as any large sterilizer.
2) Type N&S. (non vacuum assisted) (Flash).
* In, or immediately near by the operating room.
- It is indicated in emergency (in O.R.) when an irreplacable
surgical instrument is accidentally contaminated (e.g. falling
down).
- These machine are not suitable for the routine work.
* In Medical clinics.
* In all care sectors, when the risk of cross infection exists
(e.g: acupuncture)
* In dentistry clinics.
* In veterinary clinics.
* Laboratories.

36. • Bioburden reduction method:
 Inactivation of cells by transfer of heat by dry,
hot air.
 Inactivation by oxidation.
 Temperature 160 – 280 ْ ◌C
• Sterilization conditions: (Holding time)
 160 ْ ◌C for 120 minutes.
 170 ْ ◌C for 60 minutes.
 180 ْ ◌C for 30 minutes.
• Cycle time :
 4 – 10 hours.

37. • Used for:
 Metal instruments.
 Glassware, ceramics.
 Powders.
 Water free oils, greases and fats.
 Waxes, paraffin, petrolatum.
• Advantages:
 Inactivation of pyrogens at temperatures above
250 ْ ◌C.
 Non-corrosive.
 Simple installation.
 Low-cost.

38. • Disadvantages:
 Long process time.
 Suitable only for limited range of materials.
 Limited packing materials.
 Not appropriate for:
- Dressings, fabrics
- Rubberware.
- Sensitive optical equipment.
 Shelf life of the sterilized items:* No
guarantee.

40. Dry heat sterilization monitoring
* Temperature thermometer
* Time time counter
Condition of good sterilization in hot air oven:
* Homogeneous circulation of air inside.
* Equal distribution all over.
* No extra – load.

41. N.B:
* All these procedures
have no effect on Prions
* SAL 10-6

42. I. Low temperature Steam
& Formaldehyde ( LTSF)
It is obsolete in many countries.
Formaldehyde used as fumigant for many years.
 At 1960, its use was exploited as sterilization
method.
Alone, formaldehyde is slowly sporicidal and
insufficiently penetrate for narrow lumen heat
labile items.
But, when used in conjunction with sub
atmospheric steam becomes a far more
reliable sterilization process.

43. Disadvantages
1. Health hazards:
 Mutagenic  Carcinogenic
 Potent allergen  Irritating odor
Although irritant but readily detected
at levels below the threshold limit
value.
2. Reliability of test spores (2 5 days
for the results)
3. Condensation & Gas layering need
aeration

44. Sterilization cycles with LTSF
1. Vacuum <50 mbar for air removal.
2. Steam admission until temperature of
73oC is attained.
3. Introduction of Formaldehyde vapor
in a series of pulses (up to 20).
4. Sterilization stage.
5. Withdrawal of Formaldehyde.
6. Steam & air flush.

45. Loads Suitable For LTSF process
• Items that can with stand 80 ْ ◌
C, steam, high vacuum &
Formaldehyde.
• Paper wrap.
• Tube < 3m long.
• Metal / plastic complex
equipment.

46. • Fiber optic equipment.
• Cotton material.
• Porous loads.
• Red rubber.
• Liquids.
• Powders.
Loads non suitable for LTSF
process

47. E/O gas is extremely
penetrative, non
corrosive and highly
effective as a
sterilizing agent.
2. Ethylene Oxide

48. Disadvantages:
1. Health hazards :
Toxic – Carcinogenic
Mutagenic – Mucus
mmb irritation.
2. Odourless at concentration < 700 ppm
(maximum exposure limit 5 ppm/8 hours
period)
So, it has to be used with
extreme caution.

49. 3. Explosive & flammable in its pure
form. So Safer, non flammable
mixture (expensive) Is used:
10% E/0 + 90% CO2
12% E/0 + 88% Freon 12
4. Very long cycle (2 6 up to 20
hours).
5. Long Aeration time for withdrawal
of toxic residues on items.
Or

50. E/O Cycles
1. Air removal by vacuum
* Chamber heated up to 55o C
2. Subatmospheric steam is introduced
to rehumidify the load.
3. Injection & exposure to E/O gas for
various times according to pressure,
temperature & gas concentration.

51. 4. Gas is finally removed & the chamber is
flushed with air.
5. Aeration time ranged from 12 hrs (in
heated cabinet) to 7 days.
It depends on :
* absorbency of the load.
* temperature & air exchange rate.

52.  What is Plasma?
3. Plasma Sterilization System

53. It is referred to as the 4th
state of the matter ( Solid,
liquid, gas & plasma) i.e. There
is liberation of free radicals like
ions, electron, neutral species+
Energy.
• Plasma cloud is globally neutral.

54. The free radicals are generated
from H2O2 in the presence of
electromagnetic waves.
• Biocidal effect of free radicals:
Binding to the functional
components of the micro organisms
causing their irreversible destruction
then the plasma will disintegrate in
micro seconds leaving only H2 & O2.

55. Sterilization Cycle (Plasma)
♣ vacuum (0.4m bar) 10 – 15 min.
♣ Injection of H2O2 in a chamber of about 175
L capacity to obtain a final concentration of
6mg/l (6 min).
♣ Diffusion.
♣ Plasma Phase (15 min). induced by an
electromagnetic wave generator, Chamber
temperature 45oC± 2oC
♣ Injection ♣ Diffusion
♣ Plasma Phase ♣ Ventilation

56. * safe & effective for thermo sensitive
equipment.
* No toxic residue.
* Relatively rapid cycle (74 85 min).
* No aeration period after sterilization.
* Assurance quality.
Advantages of sterilization by
plasma :

57. Disadvantages:
Not reliable for:
∞ Items made from cellulose (e.g. cotton,
paper) absorb water .
∞ Items need to be dry if not cycle
cancellation.
∞ Lumens with dead ends.
∞ Highly porous materials.
∞ Long tube ( >2m ) & narrow lumen (<3mm
& >30mm long) need a diffusion accelerator

58. Cycles monitoring:
for LTSF, EO & Plasma Sterrad:
* Biological indicator :
Bacillus stearothermopilus (LTSF & Plasma).
Bacillus subtilis (EO).
* Chemical indicator : strips.
* Physical indicator: Temperature &
pressure records.

59. Comparison of low temperature
sterilization Systems
H2O2 Gas
plasma
E/O
LTSF
45oC
56oC
80oC
Temperature
73o min
4/20 hrs
3- 4 hr
Time
none
High
Conc. Used:
400-1000mg/l
Toxic.: 10mg/l
High
Conc. Used: 6mg/l
Toxic.: 2mg/l
Toxicity
none
Long
Short
Airing off
V. Good
Poor
Poor
Environ friendly
Good
V. Good
Good
Efficiency
(Diffusibility)
none
Slow & irreversible
Rapid Reversible
Polymerization
Computer
Control
Spores
Spores
Testing
Moderate
High
Low
Cost / Cycle

62.  Operation with a
temporary result leading
to the elimination of most
of micro-organisms.
 Indications :
♣ If the medical device can’t
withstand the high temperature
of the autoclave.
♣ Semi critical & Non critical
devices.

63. Differences between sterilization
& Disinfection
• Disinfection
1- 105 Bacteria
105 Spores
104 Fungi
104 Viruses
(according to A FNOR
standards)
i-e if the biobwden is 106
spores after disinfection
101 spores.
• Sterilization
1- Reach the level of 10-6
spores whatever the
initial biobwden i-e
if we start by
106 spores
After sterilization
10-6 spores i-e (1 in a
million).

64. • Disinfection
2- No Packaging
Used immediately
after disinfection.
No Security.
• Sterilization
2- Packaging
So can be used at
any time
i-e Security

65. Methods of Disinfection
of devices
1) Thermal Disinfection:
washer disinfector (60oC 90oC)
2) Chemical Disinfection:
i-e Soaking in a disinfectant.
3) Thermo Chemical

66. Levels and Means
of Disinfecting Treatments
High Medium Low
Activity
-Bactericidal
-Mycobact.
-Fungicidal
-Virucidal
-Sporicidal
-Bactericidal
-Mycobact.
-Fungicidal
-Virucidal
-Bactericidal
HIV
Means
-Steam disinfector
-2% glutaraldehyde
-Formaldehyde
-Sodium hypocrite
-Peracetic acid
-Hydrogen peroxide
-Same as before
-Washer
disinfector
-Alcohol (ethanol
isopropyl) 70-9%
-Phenolic by-
products
-Same as before
-Quaternary
Ammoniums
-Ampholytics
-Aminoacids

67. Different steps
for disinfecting M.D.
☼ Decontamination: For 10 min.
☼ Rinsing: Tap water.
☼ Drying: by clean tissue.
☼ Chemical disinfection:
By immersion in a disinfectant solution.
☼ Abundant rinsing using sterile H2O. Or sterile saline
to eliminate the residues of the disinfectant solution
and to prevent recontamination.
☼ Drying:
By sterile tissue or air + alcohol spray.