Sterilization and disinfection

Overview of various methods of sterilisation and disinfection.

1. Sterilization and Disinfection Dr. Bharat Paul

2. Contents Historical background Introduction Factors Affecting Disinfection Types of disinfection Methods Of Disinfection & Sterilization Natural Methods Physical Methods 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 – 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 – Substance that prevents or arrests the growth of microorganisms. Preparations applied topically to living tissues.

10. Introduction Asepsis - prevention of contact with microorganisms. Sanitizer – Agent that reduces the number of bacterial contaminants to safe levels. Sterile – State of being free from all microorganisms.

11. Introduction Detergent – Surface cleaning agent that makes no antimicrobial claims. Acts by lowering surface tension. Cleaning – 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., Spores–have coats rich in proteins, lipids and carbohydrates Mycobacteria –cell walls are rich in lipids Prions –the most resistant known organisms to the action of heat, chemicals, and radiation !!!

14. Factors that influence the degree of killing

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.

16. Factors that influence the degree of killing

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 – Application of disinfective measures as soon as possible after the discharge of infectious material from the body of an infectious person. Consists of disinfection of urine , faeces , vomit, clothes ,hands ,dressings, apron ,gloves. Terminal disinfection - 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 – 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

29. Methods of disinfection Natural methods Physical methods Chemical methods

30. Natural agents Sunlight – UV rays of sunlight lethal to bacteria and some viruses. Articles such as linen, bedding and furniture may be disinfected. Air Acts by drying or evaporation of moisture which is lethal to most bacteria.

31. Physical agents Burning Inexpensive articles such as contaminated dressings , rags and swabs – disposed off by burning. Best done in an incinerator. Addition of sawdust, paper ,kerosene or other combustible material aid in burning.

32. Physical agents Hot air Articles such as glassware ,syringes , swabs , dressings and sharp instruments. Drawback – no penetrating power: not suitable for bulky materials. Hot air oven – 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 Boiling Autoclaving Pasteurization

35. Physical agents Boiling for 5-10 minutes :kill bacteria but not spores or viruses. Temp. above 100 deg C required for destruction of spores. Disinfection of small instruments , tools not used for subcutaneous insertion , linen and rubber goods such as gloves. Slow process , unsuitable for thick beddings and it fixes albuminous stains.

36. Physical agents Autoclaving Operate at high temperature and pressure. Destroys all forms of life , including spores. Sterilization of linen , dressings , gloves , syringes , instruments and culture media. Not suitable for plastics and sharp instruments.

37. Autoclave

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 fluid’s palatability. Conditions: 62℃, 30min or 71.7℃, 15sec Significance: kills vegetative pathogens.

39. Pasteurisation

40. Physical agents Radiation Sterilization of bandages , dressings , catgut and surgical instruments. Great penetrating power with little or no heating effect. Most effective ,but very costly. Normally 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. Don’t 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) – not an effective disinfectant Crude phenol - phenol and cresol. effective against gram + ve and – ve organisms. Cresol – used in 5 to10 % for disinfection of urine and faeces . Cresol emulsions – very powerful disinfectants

44. Chemical agents Chlorhexidine ( hibitane ) – most useful skin antiseptic. 0.5% solution used as handlotion.1% creams used for burns Hexachlorphane – slow in action , but shows cumulative effect on skin and is compatible with soaps. Dettol ( chloroxylenol ) – relatively non toxic antiseptic.5 % dettol for disinfection of instruments and plastic equipments.

45. Chemical agents Quaternary ammonium compounds Cetrimide ( cetavlon ) bactericidal against vegetative gram + ve organisms , much less against gram - ve Used in 1-2 % strength Savlon Combination of cetavlon and hibitane . Plastic appliances may be disinfected in 20 min. 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 ( Betadine ®), 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 Highly toxic and irritant gas Effective against vegetative bacteria ,fungi and many viruses. Used as a 2-3 % solution for spraying rooms , walls and furniture Most 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 – 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 Cheapest disinfectant Used as fresh quick lime or 10-20 % aqueous suspension known as milk of lime. Faeces and urine disinfected by 10-20% aqueous solution (in 2 hrs). Used as a deodorant in public places where toilets are located.

55. Chemical agents Ethylene oxide for heat sensitive articles At 55- 60 deg C : kills bacteria ,spores and viruses. Mixed with 12 % carbon dioxide (as it is explosive) Water vapor added to the mixture to increase efficacy. To sterilize fabrics, plastic equipment , cardiac catheters , etc.

56. Some Newer agents Bacillocid ® rasant Formaldehyde-free disinfectant cleaner with low use concentration Virkon gaining importance as non Aldehyde compound Disinfects medical devices and lab equipments. 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 121ºC 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 Bowie Dick tape is applied to articles being autoclaved. Before heat exposure, the tape is uniformly buff in color. 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 – 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 Clean the affected area with soap and water then disinfect with a 1%Na hypochlorite solution for 15 minutes. HIV infected articles Cleaning and 2% glutaraldehyde for 30 minutes. 6% Hydrogen peroxide for 30 minutes. 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 23 rd edition. CDC – Sterilization and disinfection guidelines Hospital hygiene and infection control –WHO. WHO Pharmacoepia Library- Methods of Sterilization. Occupation Safety and Health administration- Disinfection guidelines.