• INTRODUCTION
  The effective use of antiseptics, disinfectants and sterilization procedures is an important part of preventing nosocomial infections. The choice of disinfectants is dependent on several factors like the degree of microbial contamination or the bio-burden, the device to be disinfected, the cost and the availability of the agent.

• Sterilization is defined as the use of a physical or chemical procedure to destroy all microbial life, including bacterial spores. In practices, this refers to microorganisms that may exist on inanimate objects. The common methods include moist heat by steam sterilization, ethylene oxide gas or dry heat.

• Disinfection is a less lethal process than sterilization. It eliminates pathogenic microorganisms, but not necessarily all microbial forms.

• Decontamination is a term used to describe a process that renders a medical device, instrument or environmental surface safe to handle. This may range from simple cleaning with soap and water to sterilization and disinfection.

• Antisepsis is a term used for the destruction or inhibition of microorganisms on the skin or living tissues.There are two main applications of disinfection :

• To destroy  organisms present on delicate or heat sensitive instrument which cannot be sterilized.
• General purpose disinfection to minimize infection hazards for respiratory, enteric or other pathogens present on floors, wall, furniture and other inanimate objects.

A simple classification was proposed by EH Spaulding in 1968, to provide a rational approach to disinfection and sterilization of patient care  items. The three categories of items he described were critical, semi-critical and non-critical.

Critical Items
These  are items that enter sterile tissue or the vascular system. They must be sterile and free of all microbial life including spores, because any microbial contamination could result in the transmission of an infection. This category includes surgical instruments , cardiac and urinary catheters, implants and ultrasound probes used in sterile body cavities. These items are preferably sterilized by steam sterilization.
Heat sensitive items may be sterilized by ethylene oxide gas, hydrogen peroxide gas plasma or by liquid chemical sterilants.
Liquid chemical sterilants  includes gluteraldehede (>2.4%) peracetic acid (0.2%) or stabilized hydrogen peroxide (7.5%). These can be relied upon to produce sterility only if cleaning, to eliminate organic and inorganic material precedes treatment and if proper guidelines as to the concentration, contract time, temperature and ph are met.

Semi-critical items
Semi-critical items are those that come in contact with mucous membranes or non-intact skin. This includes respiratory therapy and anesthesia equipment, endoscopies, laryngoscope blades, esophageal manometry probes. These devices must be free from all microorganisms, although a small number of bacterial spores may be present. Semi critical items require high level disinfection with chemical disinfectants. The FDA approved high level disinfectants are gluterldehyde, hydrogen peroxide , orthopthaladehyde and peraceticacid in the recommended concentrations. The minimum contact time should be 12 minutes.

Laparosopes and arthroscopes entering sterile tissues should ideally be sterilized between patients. However, sometimes they undergo high level disinfection with gluteralldehyde. A note caution: meticulous cleaning must precede any disinfection / sterilization process. The instruments must be dismantled before cleaning and disinfection. Never models can withstand steam sterilization and should be given preference.

High level disinfection should be followed by rinsing with sterile water. In case this is not feasible, filtered water should be used and followed by an alcohol rinse and forced air drying. Items should be dried and stored such that are protected  from recontamination.

Outbreaks of atypical mycobacterial infection of the skin have been reported due to contaminated water being used for the rinse/cleaning of scopes.

Non-critical Items
Non-critical items are those that come in contact with intact skin but not mucous membranes. Intact skin acts as a barrier to most microorganisms. These include bedpans, blood pressure cuffs, stethoscopes, linen, furniture floors etc. There is no documented risk of transmitting an infectious agent via such items to patients. However, such items could contaminate the hands of healthcare workers and serve as a means of secondary transmission. Non critical items are treated with low level disinfectants.

The commonly used disinfectants in this category include ethyl/isopropyl alcohol (70-80%), sodium hypochlorite (100ppm), which are intermediate level disinfectants and quaternary ammonium compounds and iodophors which are low level disinfectants.

Housekeeping surface are usually cleaned with a detergent disinfectant or a detergent or sanitizer. Detergent disinfectants and sanitizers should be diluted according to the manufacturer’s instructions . The routine use of disinfectants to disinfect hospital floors and other surfaces is controversial, because there is little risk of transmitting pathogens to patients. However, spills of blood or body fluids must be treated with a disinfectant.

Special Issues
Care of blood and body fluid spills
Sodium hypochlorite is the agent of choice. Use USP grade 5% solution, diluted 1:50 for low risk and 1:5 for high risk. The dilution should be in tap water and the solution prepared freshly each day.

Formaldehyde-alcohol no longer plays a role in high level disinfection because it is corrosive, irritating and toxic and formaldehyde is carcinogenic.

Choice of disinfectants
The market is flooded with disinfectants. It is necessary to look into the active ingredients of the brand rather than by the claims of manufacturers.

The evaluation of disinfectants is a complex process. It is therefore inadequate to look at results of in-vitro tasting against certain pathogens and or standard strains of microorganisms alone. There is an additional need for in-situ evaluation i.e. measuring viable contamination before and after application to a selected surface.

There is an essence “one” ideal disinfectant.

Each application requires careful evaluation with respect to the following :

• Type and number of microorganisms
• Type and amount of organic matter.
• Contact time.
• Type of surface.
• Type of water for dilution i.e. hard/soft.
• Manufacturers’ data on efficacy.
• Safety and environmental acceptance.
• Cost.
• Shelf life and convenience.
• Residual activity.

 
Useful properties of some common disinfectants and antiseptics
Chlorhexidine gluconate 2% or 4% w/v is a biguanide and is used for skin antisepsis.It has residual action and also acts in the presence of organic matter. It is neurotoxic and should not be used on the face and hair. For environmental purpose, it is often combined with cetrimide, a quarternary ammonium compound with excellent detergent properties. This is useful for environmental cleaning and can also be used for cleaning and decontamination of surgical instruments, for the treatment of contaminated colored linen and fibreoptic scopes.

Iodophors : The environmental iodophors are a separate formulation. They do not act in the presence of organic matter and they lack residual activity.
Povidone iodine used for skin antisepsis should be 10%. Allerdies are common to iodine.
In case of allergy to both chlorhexidine and iodine use ordinary soap followed by alcohol rub.
Triclosan 1% has useful acitivty against methicillin resistant Staphylococcus aureus.
Triclosan based antiseptics are therefore useful for hand washing in such cases .Bathing soaps containing this are also useful as shampoos in hospitalized patients.  
Sodium hypochlorite, used appropriately can be for the care of spills, for environmental disinfection and cleaning, for contaminated white linen, for the cleaning and disinfection of bedpans and urine pots. It is also economical and should be avoided for surgical instruments and on other metal surface unless diluted. This is available as tablets, and as household bleach. If bleaching powder (Calcium hypochloride) is used as an alternative the chlorine content is 70% available chlorine. This is to be used in a concentration of 7gms / litre.

Stabilized hydrogen peroxide is another useful disinfection for surface cleaning, fogging etc. It is also corrosive and should be diluted appropriately before use.

Alcohol has disinfection properties only when diluted to 70-80%.
Hand rubs containing chlorhexidine and alcohol have the advantage of residual activity of chlorhexidine and are preferred to other combinations.

STERILIZATION:
Medical devices classified as critical devices should be sterile when used because any microbial contamination could result in disease transmission. These items include surgical instrument, biopsy forceps and implanted medical devices. If these items are heat resistant, the recommended process of sterilization is with steam.

Steam sterilization
This method has the largest margin of safety due to its reliability, consistency and lethality. Steam sterilization is non toxic, inexpensive, rapidly microbicidal, sporicidal and rapidly heats and penetrates fabrics. Moist heat in the form of saturated steam under the pressures is most dependable.

Principle: exposure of the item to direct steam at the required temperature and pressures for the specified time.
Important steps for steam sterilization

• Items to be sterilized must be prepared to permit air removal and ensure contact of stem with all
  surfaces of the devices.
• Provide protection for sharp and delicate instrument. It is myth that sharps blunt in steam sterilizers.Blunting is the result of poor quality of autoclaves.
• The items should be thoroughly cleaned to reduce the bioburden and tested to verify functionally
• The items should be appropriately packaged.

Packaging  : is required to allow sterilization of the contents and the material used should be compatible with process and it should maintain sterility until the pack is opened. There are several types of packaging material available. Linen packs are likely to get contaminated easily since linen allows microorganisms to pass particularly if the pack is moist and extensively handled. Paper pack, non-woven material and medical grade are the alternatives.
The shelf life of the packaged sterile items depends on the quality of the wrapper the storage conditions, transportation conditions and handling. Sterile items should be stored in a clean room.

Autoclaves
The choice of autoclaves is important. The sterilization system is the heart of the surgical services. Investment in a good quality autoclaves is therefore essential. The shelf life of an autoclave is at least 20 years.

There are two basic types of autoclaves :
Gravity displacement which evacuates air by heating and gravity.
Prevacuum is mechanized evacuation of air.
Lack of air removal hampers with the process of sterilization.
Autoclaves need to be properly maintained. The manufacture is responsible for the calibration and validation checks.
There are four important parameters

• Dry saturated steam
• Pressure which serves as a means to quickly obtain the required temperature
• Temperature 121 degrees Celsius or 134 degrees Celsius
• Time 30 minutes at 121 degrees and 4 minutes at 134 degrees

These physical parameters need to be monitored with every cycle. Record keeping of loads, parameters and validation are important to safeguard the practioners interest.
Most of the sterilizers in use are gravity displacement and the only record available is the pressure, what is actually required is the temperature record.
Thus a quality sterilizer indicates the temperature.

Validation systems for sterilization
Steam Indicator tapes:
These are used as external chemical indicators to immediately indentify processed items and also serve as a closure tape to seal sterilization packs. The chemical indicator lines turn dark brown when exposed to a steam sterilization process.

Steam Chemical Integrators
These are internal chemical integrators used for pack control, which validates that the steam has penetrated to the point of placement in the pack and confirms that sufficient exposure conditions have been met. This is a chemical indicator consisting of a paper wick and steam and temperature sensitive chemical pellet contained in a paper/film/
Foil laminate envelope of laminate material. Steam enters the permeable topside of the device-the chemical pellet melts and migrates as a dark color along the paper wick; the distance or extant of migration depends on exposure to steam, time and temperature, The migration is visible through a window marked Accept of Reject. The dark color has not entered the Accept window, a reject result is indicated.

Biological Indicators
The effectiveness of steam sterilization is monitored with a biological indicator containing spores o Geobacillus stearothermophillus. Positive  spore test result  are an indicators of inadequate steam delivery or equipment malfunction.
The validation process should consist of a biological indictor at least once a week.
Every pack should carry a temperature sensitive tape which indicates that the item has passed through a cycle. This tape does not validate the cycle.

Ethylene Oxide
This is a low temperature method of sterilization which is recommended for heat and moisture sensitive items. The packaging system consists of sealed cellophane or plastic bags. ETO gas is carcinogenic and the sterilization items required proper aeration on another chamber. This increases the turn around time to nearly 16 hours. Plastic items that are to be sterilised must be dried adequately because EO gas reacts to form a highly toxic compound. Many of the single use devices that are being reused are gas sterilized.

NEWER TRENDS IN STERILIZATION
Hydrogen Peroxide Gas Plasma Sterilization
This method is also useful for temperature and moisture sensitive items, the temperature being 50 degrees Celsius. It is safe for the environment and the healthcare worker, it leaves no toxic residue. It has a short cycle time 45-75 minutes and needs no aeration. It is simple and easy to operate and is compatible with most medical devices. Currently the high cost of the equipment is a major limitation and it requires synthetic packaging of polypropylene and a special container tray. Linen and liquids cannot be processed.