Dental Tribune United Kingdom Edition

M ost equipment-associ- ated infection is due to inadequate cleaning and disinfection. The most ef- fective stage of any decontami- nation procedure is thorough cleaning. Medical devices heavily loaded with microbiological material will be more difficult to sterilise than one lightly contaminated and must there- fore be thoroughly cleaned to reduce organic material or bioburden before disinfec- tion and sterilisation. Washer- disinfectors are the safest and most reliable option. Automated processors, eg washer disinfectors and ul- trasonic cleaners, improve the quality of the decontami- nation process and offer the safest, most reliable option, providing they are suitably monitored and maintained. Decontamination is done most simply in a disinfec- tor which both cleans and disinfects in one stage. In a washer-disinfector the items are first cleaned by rinsing in cold water and then washed in water at less than +70oC. The water temperature then increases to between +85oC and +93oC, for one to three minutes, providing thermal disinfection of the load. At the temperature range of +85oC - +93oC, pathogenic bacte- ria are inactivated or killed, but bacterial spores survive. In order to ensure inactiva- tion of viruses, particularly hepatitis virus which is rela- tively heat tolerant, it is now recommended that the water temperature during the dis- infection phase should be just over +90oC. Disinfection is generally a less lethal process than steri- lisation. It eliminates virtu- ally all recognised pathogenic microorganisms but not nec- essarily all microbial forms (eg bacterial endospores) on inanimate objects. Disinfec- tion does not ensure overkill, and therefore disinfection processes lack the margin of safety achieved by sterilisa- tion procedures. Cleaning and disinfection of instruments should be car- ried out as soon as possible after use. Dried biological ma- terial is much more difficult to remove than fresh deposits. Blood, with its content of iron, acid and sodium chloride, is corrosive. The type B-cycle Sterilisation is defined as the use of a physical or chemical procedure to destroy all mi- crobial life, including large numbers of highly resistant bacterial endospores. The ste- rility requirement for medical products means that the theo- retical probability that a living organism will be present on an object after the sterilising process is equal to or less than one in a million, so-called Sterility Assurance Level (SAL) = 10-6. Sterility may be achieved by various methods: heat, chemical and ionising radiation. The simplest meth- od is heat sterilisation. There are two methods: dry heat sterilisation, ie use of dry heat usually a hot air oven or au- toclaving, in which moist heat (steam) is used. Regardless of the method, the result of sterilising proce- dures depends on the number of microorganisms and other biological material present on the article before inacti- vation and the resistance of microorganisms to the steri- lisation process. The result of steam sterilisation is also in- fluenced partly by the kind of material the items are made of, and partly by the shape of the items. It is important to note that packaging material itself is a porous load (pa- per, textiles) and should be handled as such. All pack- aged/wrapped goods require sterilising in steam-autoclave processes with pre- and post- vacuum cycles. Another factor which in- fluences the result of the sterilising procedure is the way in which the chamber is loaded as well as whether the items are packaged and the shape of the package. The goods should not be tightly packed: the steam must be al- lowed to penetrate all parts of the goods. Residual moisture in the packaging material af- ter sterilisation will act as a potential pathway for micro- organisms to penetrate the package. Steam sterilisation Saturated steam under pres- sure is by far the quickest, safest and most efficient and most reliable medium, known for the destruction of all forms of microbial life. The brief exposure to steam destroys the most resistant bacterial species and heat is rapidly achieved because of mass heat transfer as the steam condenses. In order for the steam to condensate within the whole load to be sterilised, virtually all air must be evacuated dur- ing pre-treatment. This can only be achieved with several (at least three (3)) pre-vacu- um pulses. So called B-cycle in accordance with EN 13060. In steam sterilisers with pre- and post-vacuum pro- cesses (ie B-cycle), the steri- lisation process is composed by three main phases: pre- treatment, sterilising and post-treatment. During pre- treatment the air is expelled by a number of pulses of vacuum and the introduction of steam. The temperature increases successively, up to the degree at which sterilis- ing is to take place. The actual sterilisation period, which is called holding time, starts when the temperature in all parts of the autoclave cham- ber and its contents (the load) have reached the sterilising Dr Mikael Zimmerman discusses disinfection “Sterile” does not mean clean and safe June 4-10, 201216 Infection Control Tribune United Kingdom Edition Fig 1 Endofile, sterilised but not properly cleaned and decontaminated before the sterili- sation process. In this case sterilisation will fail Fig 2 Washer disinfectors offer the safest and most reliable option for decontamina- tion and disinfection. Tray systems must allow water jets to reach every part of in- struments to clean and inactivate efficiently Fig 3 In the case of ultrasonic cleaning instruments are best cleaned if instruments are fastened but free and have no contact with locking device Fig 4 A common problem in many clinics is an overload of instruments Fig 5 To organise the logistics and han- dling of instruments requires a lot of time – tray systems offers a better solution Fig 6 Corrosion is a common problem when mixing different materials in the same fluid – as is the case with aluminium and stainless steel. Corrosion pits increases the possibilities for microorganisms to at- tach themselves to the surface Fig 7 Efficient trays should be made out of non-heat absorbing, non-heavy and non- corrosion causing material Fig 8 Stands for burs and endofiles are often a problem – a simple solution is to use standard kits and pre-prepared trays Fig 9 Good and safe handling of instru- ments with pre-prepared trays saves time and money at the same time as quality will be improved Fig 10 Tray systems should facilitate the handling of instruments through the whole hygienic circle