Conventional techniques for attempting to remove potentially infectious or contagious bacteria and viruses from surgical, dental or veterinary instruments are not totally reliable, particularly in the cases of pathogenic agents such as particles of single strand DNA and in particular proteins of CJD (Creutzfeldt-Jakob disease) and BSE (bovine spongiform encephalopathy), and related spongiform encephalopathies (SEs), for example, scrapie. It is thought that these particles are held to the surface of instruments by an electric charge, whereby conventional solutions fail to kill, render inert or release the particles from the instruments, and subsequent use of the instruments can lead to progress of the disease.

Of major concern to the inventor is preventing the spread of CJD, BSE and related SEs, bacteria and other bacterial hospital- borne infections particularly where the presence of such disease causing agents may not be appreciated by surgeons using the instruments to be sterilised.

It would therefore be desirable to be able to provide a method and means of sterilising medical instruments which effectively ensured the removal of, inter alia, electrically charged proteins and the like from the instruments without the necessity for scrubbing or other physical abrasion. The term sterilising'is used herein to refer to removal of disease causing agents, but because the rinsing step may use tap water, the term does not necessarily infer that the process results in

instruments which are sterile'according to common medical terminology.

According to one aspect of the present invention there is provided a method of sterilising medical instruments comprising the steps of: (i) soaking the instruments in an alkaline solution, which is preferably heated, in particular a solution of caustic soda (sodium hydroxide) or potassium hydroxide, containing a repellent, such as sodium dodecyl sulphate (SDS); and (ii) subsequently rinsing the instruments to remove all traces of the solution therefrom.

The heated alkaline solution ensures the inactivation of all known bacteria and viruses, except CJD and BSE, while the repellent properties of SDS ensures the removal of the CJD and/or BSE proteins from the instruments.

The solution is preferably heated to a temperature of between 50°C and 85°C, more preferably to a temperature of around 70°C, typically for a period of up to 30 minutes. However, the solution can be used at room temperature.

It is further preferred that the method includes, for example, three rinses each of about 5 minutes in length.

The alkali in the solution is preferably sodium hydroxide or potassium hydroxide, but may be any suitable alkali, for example, ammonium hydroxide, which is, however, less preferred.

The alkali is preferably present in a concentration of between 0.5 and 2 molar, although the upper limit may be higher or lower than this. The amount of alkali in the solution should not be such as to cause substantial corrosion to the instruments being sterilised.

The repellent is preferably sodium dodecyl sulphate (SDS), but may be replaced by any other suitable anionic surfactant. In particular, the counter ion of the surfactant (sodium) may be varied, as well as the hydrophobic chain length (from 12 carbon atoms to, for example, 10 or 14 carbon atoms). The amount of repellent in the soaking solution is preferably between 0.5 or 1 and 3 or 5% by weight, with an amount of 1% by weight being most preferred.

A further optional component of the solution is iodine or bromine. The inclusion of iodine or bromine in the solution can give a more effective sterilisation. Without wishing to be bound by theory, the addition of iodine or bromine to an alkaline solution results mainly in the formation of the oxoanions IO-, 103-, BrO-and Br03-. These oxoanions act as oxidising agents so as to render proteins, protein fragments, DNA or DNA fragments substantially inert. The alkali, for example, sodium hydroxide solubilizes (e. g. disintegrates) the agents to be sterilized. The repellent, for example, SDS, also assists in the solubilization process. Suitable surfactants, such as SDS, also tends to remove electric charge from the agents to be sterilized. This allows the disease causing agents, e. g. proteins or DNA or fragments thereof to be de- bonded from a surface of, e. g. a surgical instrument. The combined effect of the alkali (e. g. sodium hydroxide) and repellent (e. g. SDS) is to increase the surface area of agent on which the oxoanions produced by the iodine or bromine can have an effect.

The iodine or bromine are preferably added in an amount of between 0. 01% and 0. 2% by weight, with 0. 1% by weight being preferred.

Optionally, the iodine or bromine may be supplemented by, or wholly or partially replaced by Ruthenium red, a known staining composition. If present, Ruthenium red is effective at

concentrations as low as 1 part per million (ppm), up to preferably 100 ppm, with 10 ppm being a more preferred maximum.

Ruthenium red binds to acid mucopolysaccharides or acid mucoproteins (e. g. in protein/DNA complexes).

Preferably, the solution is aqueous. A particularly preferred solution is 1 molar sodium hydroxide, 3% SDS and 0. 1% iodine (percentages expressed as weight percent per 100g water).

However, the concentrations of each component in this solution could, independently, be at least 0.5 molar sodium hydroxide, 0. 5% SDS and 0. 01% iodine. Typically, the useful upper limit of these concentrations is determined by the limit of the acceptable corrosivity of the solution, which will depend on its application.

This composition is effective to combat BSE/CJD by sterilizing surfaces of surgical equipment or other surfaces or apparatus.

However, it is also effective to combat other agents such as bacteria, typically those which cause hospital-borne infection.

The soaking of the instruments in the alkaline solution according to the first aspect of the present invention may be accomplished in a number of ways. For example, the instruments may be immersed in water first, and then a concentrate or powder added to produce the appropriate concentration of soaking solution. The strength of the concentrate will be determined by the solubility of the components used, but may be a lOx, 20x or 50x concentrate if possible. A suitable mixture of powdered components may also be provided.

The method may also include the step of agitation, i. e. subjecting the solution in which the instruments are, or the instruments, to agitation. If the agitation is of the instruments, this may occur by agitation of a container in which the instruments are held.

The method may also include the step of treating the instruments by sonication, i. e. subjecting the solution in which the instruments are to ultrasound, which preferably has a frequency of 20 kHz or higher, more preferably about 30 kHz. This step may be repeated at various stages of the method, as appropriate, for example, during the soaking stage and at the end of each rinsing stage.

Both these additional steps are thought to help in releasing any particles attached to the instruments and to treat down any aggregation of particles present.

A further preferable method step to follow steps (i) and (ii) is to soak the instruments in an aqueous solution of iodine and or bromine. This further soaking step is carried out without any alkaline or repellent. Without wishing to be bound by theory, iodine and bromine are thought to bind sites on the agent (e. g. protein or DNA, after solubilization) to render it substantially inert or ineffective. This makes the agent inactive for reinfection. The iodine or bromine are preferably present in the solution in an amount of between 0. 01% and 0.2% by weight, with 0. 1% by weight being preferred. As in the first soaking step they may be replaced by Ruthenium Red, present in an amount which may be as low as 1 part per million (ppm), up to preferably 100 ppm, with 10 ppm being a more preferred maximum.

Such a further soaking step is followed by a further rinsing step, wherein the first rinsing solution is preferably an alkaline solution, for example of 0.05 to 0. 2 M sodium hydroxide. In such a case, there may follow two or three rinses with water. If an alkaline solution is not used as the first rinsing solution, then two or three rinses with water may be used.

The solution used in the first step of the method of the first aspect of the invention is another, independent aspect of the

invention. Accordingly, in a second aspect of the present invention, there is provided a solution as described in the first aspect of the invention, ie. an alkaline solution containing a repellent. Preferred embodiments of this aspect are described above in relation to the first aspect of the invention.

In a third aspect of the present invention, an apparatus suitable for carrying out the method of the first aspect is provided. The apparatus for sterilisation, e. g. for sterilising medical instruments according to the preferred method of the invention, comprises a container having a water inlet in the upper regions thereof, an outlet from the lower regions thereof for waste, support means for locating the instruments to be sterilised within an intermediate region of the container, and heating means for heating the solution within the container.

Preferably the apparatus further comprises a fan within the container, activated, for example, to circulate the solution when the temperature thereof reaches the optimum value of, typically 70°C during the sterilisation process, and to circulate rinsing water during the rinsing stages. This fan can also be used for agitating either the soaking solution or the rinsing water.

The support means may comprise a grid or mesh through which the solution and the rinsing water can readily pass.

The apparatus may also further comprise an ultrasound generator for carrying out sonication (preferably at a frequency of at least 20kHz, more preferably at about 30kHz), and means for dispensing a concentrate or powder precursor to the soaking solution.

Many of the components of apparatus are conventional and well known to the person skilled in the art.

The apparatus may be combined with an autoclave.

Fig. 1 is a schematic section through apparatus for carrying out the method of the invention, the apparatus including a container 2 having an inlet 4 to the upper regions thereof and an outlet 6 from the lower regions thereof.

A grid or mesh 8 is provided above the level of the outlet 6 to support thereon surgical instruments 10 to be sterilised.

A heating element 12 and a circulating fan 14 are provided in the lower regions of the container 2 below the grid 8. A sonicator (not shown) may also be provided in this region of the container 2.

The container 2 is provided with a lid 16 and has a liquid level indicator 18 therein.

The apparatus is used as follows: Water is fed through the inlet 4 to the level 18 within the container. 3% sodium dodecyl sulphate (SDS) in powder form and one mole sodium hydroxide in pellet form are added to the water, the lid 16 is located on the container 2, and the apparatus is switched on. A short period (e. g. 3 to 5 minutes) of ultrasound treatment may be carried out, to dislodge particles from the instrument 10, and to break up any aggregated particles. To improve effectiveness, the solution may contain 0. 1% iodine and/or at least 1 ppm Ruthenium red.

The heating element 12 heats the solution up to a temperature of, typically 70°C and maintains this temperature, for around 30 minutes. As the temperature of the solution reaches the desired value, the fan 14 is automatically activated to circulate the solution within the container 2. The fan 14 may also be used to agitate the water, or the surgical instrument 10 may be directly

agitated, eg. by agitation of a basket (not shown) containing them.

During the soaking period, the caustic soda destroys all known bacteria and viruses except CJD and BSE proteins, SDS within the solution acting as an electrical repellent whereby any CJD or BSE proteins are physically unbound from the instruments 10 into the solution. The iodine/Ruthenium red products inactivates these proteins by binding to them.

Once the 30 minutes time period has expired, and after an optional short period of sonication, the solution is drained from the container 2 through the outlet 6, the grid 8 allowing the liquid to pass therethrough whilst maintaining the instruments 10 within the container 2.

Water is then fed into the container 2 through the inlet 4 to the level 18 and is circulated in the container 2 by the fan 14, typically for a period of about 5 minutes, after which it is drained from the container 2 through the outlet 6. Again, agitation or ultrasound treatment may be carried out during each rinsing stage.

This rinsing procedure is repeated for, for example, two further periods of 5 minutes each such that all the NaOH/SDS/iodine solution is removed from the instruments 10 and from the container 2.

Preferably, a further soaking step is carried out with a 0. 1 % by weight solution of iodine, for 30 minutes (optionally including sonication), followed by a first 5 minute rinse with a 0.1 M sodium hydroxide solution and second and third rinses of five minutes with water.

The instruments 10 can then be removed from the container 2 knowing that they are sterile-i. e. all known bacteria and

viruses have been inactivated, and any CJD and/or BSE proteins have been removed due to the repellent properties of SDS, and rendered inert by the iodine.

Clearly the precise constituents of the solution, as well as the temperatures and time periods specified above, can be varied without departing from the scope of the invention. In particular, the sodium hydroxide may be replaced by, for example, potassium hydroxide.