Abstract:
A device useful in determining the efficacy of a chemical sterilization process includes a dead end cavity closed by an access cap having a port coupled to a challenge tube defining the only path by which a substantial quantity of sterilant can reach the cavity. A biological indicator is located within the cavity and a chemical indicator is also provided. These indicators, and particularly the biological indicator, provide an indication of whether chemical sterilant would reach all interior exposed surfaces of a load in sufficient concentrations to adequately sterilize the load.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Contract No. W81XWH-05-1-0398 awarded by USA Medical Research ACQ Activity; Office of Naval Research SBIR Phase II, Contract No. N00014-06-M-0301 and Contract No. 5R44HL074653-03 awarded by National Institute of Health SBIR Phase II. 
    
    
     CROSS-REFERENCED TO RELATED APPLICATIONS 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention relates to evaluating the efficacy of sterilization processes. More specifically, the present invention provides a useful tool for evaluating whether a sterilization process effectively deactivates biological contaminants within a load to be sterilized, including contaminants residing within the most difficult-to-sterilize locations of the load. 
     II. Related Art 
     Various sterilization processes have been employed to eliminate biological contaminants from a load. Such a load, for example, may comprise one or more medical or dental instruments or supplies. Some of these sterilization processes involve the use of a sterilant chemical chosen because it will destroy bacteria and other biological contaminants on the surface of a load if delivered to the surface at an appropriate concentration and for an appropriate period of time. One commonly used sterilant chemical is hydrogen peroxide. When the load has interior exposed surfaces, sterilization will only be successful if the entirety of all interior exposed surfaces is brought into contact with the sterilant at sufficient concentrations and for a sufficient period of time to destroy all biological contaminants present on such surfaces. Biological contaminants not eradicated from medical or dental instruments or supplies prior to use can be transferred to a patient leading to infection. 
     Much research has been undertaken to develop effective chemical-based sterilization processes. Various test packs have also been developed to attempt to test the efficacy of such processes. These test packs typically provide various paths from the exterior of the test pack to an interior chamber where one or more indicators are located. These indicators often include a chemical indicator which changes color when exposed to the sterilant. These indicators also often include a biological indicator housing organisms which are deactivated if sterilant of a sufficient concentration reaches the biological indicator over a sufficient period of time. Such devices are sometimes referred to as “process challenge devices” because they are intended to present a defined challenge for test purposes comparable to the challenge presented by the most difficult item to be sterilized in a load to be sterilized. 
     Existing process challenge devices suffer from a variety of problems leading to inaccurate test results. Some problems result from blockage of the aforementioned paths. Such blockage can occur as a result of condensation occluding the path between the interior and exterior of the device. Such blockages can also be the result of pressure changes in the sterilization chamber related to the process being tested causing the walls surrounding the path to collapse. Other problems arise if the challenge presented is either more or less difficult than required given the attributes of the contents of a load to be sterilized. Still other problems arise as a result of the number and spacing of access points into the path from the exterior of the test pack. When multiple access points are present, controlling the degree of challenge is made more difficult and obtaining repeatable test results becomes problematic. Existing process challenge devices are also often difficult or expensive to manufacture. The present invention overcomes these and other problems. 
     SUMMARY OF THE INVENTION 
     The present invention relates to process challenge devices used to test the efficacy of sterilization equipment, methods and protocols. In one embodiment, the process challenge device comprises an assembly including a housing having a first dead end, a second open end, and an interior cavity. The dead end can be formed using a plug or by forming the housing to provide the dead end. The assembly further comprises an access cap sealing the open end of the housing. The access cap has a port. Coupled to the port is a challenge tube having a lumen extending along the entire length of the challenge tube. The challenge tube is joined to the port of the access cap such that the only path by which a substantial quantity of sterilant can enter the cavity is the path defined by the lumen of the challenge tube and the port. The length of the challenge tube and diameter of the lumen are selected to present a desired challenge. 
     Before sealing the open end of the housing with the access cap, a biological indicator is positioned within the cavity. In some embodiments, the assembly may also include a sterilization pouch surrounding the housing and challenge tube. Whether or not such a pouch is used, a chemical indicator is coupled to the assembly. The chemical indicator can be placed within the interior cavity of the housing or otherwise affixed to the housing, plug, access cap, challenge tube, or sterilization pouch of the assembly. The chemical indicator provides an immediate visual indication (such as a color change) when a predetermined amount of sterilant has come into contact with the chemical indicator. 
     The biological indicator may, but need not be, self-contained. Self-contained biological indicators typically include a known load of microorganisms and a medium, that when brought into contact with any viable microorganisms, will provide an indication of the presence of viable microorganisms. Other biological indicators only include a load of microorganisms. After the test, the load of microorganisms is then tested to see if any remain viable. 
     Process challenge devices made in accordance with the present invention are used to periodically verify, through chemical and biological evaluation, that a sterilizer and the sterilization process carried out using the sterilizer are fully functional. For example, process challenge devices are used both for installation qualification of a sterilizer and routine verification of sterilizer operation. The process challenge device provides a challenge between the sterilizing environment and the biological and chemical indicators intended to represent the most challenging location for sterilant to reach in an actual load to be sterilized. Sterilant must overcome the challenge posed by the process challenge device to trigger a passing response from the biological indicator and chemical indicator if a chemical indicator is provided, thus indicating the sterilization process carried out using the sterilizer is effective. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a first embodiment of the process challenge device of the present invention. 
         FIG. 2  is another perspective view of the process challenge device shown in  FIG. 1 . 
         FIG. 3  is an exploded view of the process challenge device shown in  FIG. 1 . 
         FIG. 4  is an end view of the process challenge device shown in  FIG. 1 . 
         FIG. 5  is a sectional view of the process challenge device taken along the line A-A in  FIG. 4 . 
         FIG. 6  is a perspective view of a second embodiment of the process challenge device of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The process challenge device of the present invention provides an inexpensive, easy-to-assemble and disposable device used to verify that a sterilizer and associated sterilization process are fully functional to destroy biological containments in a load. As shown in  FIGS. 1-5 , the process challenge device  10  comprises a housing  12 , a plug  14 , an access cap  16  and a challenge tube  18 . As shown in  FIG. 6 , the process challenge device  10  may also include a sterilization pouch  60 . The process challenge device  10  also includes a biological indicator  30  and an optional chemical indictor  50 . 
     The plug  14  closes one end of the tubular-shaped housing  12  to provide the housing  12  with a cavity  20  with a dead end  22 . Those skilled in the art will recognize that the housing  12  can be formed in a way in which the dead end  22  of cavity  20  is created without a plug  14 . 
     The other end  24 , referred to as the open end, of the housing  12  is closed by access cap  16 . The access cap has a flange  17  to facilitate removal of the access cap  16  from the housing  12 . The access cap  16  has a port  26  extending through the access cap  16  to which the challenge tube  18  is coupled as best shown in  FIGS. 3 and 5 . Tube  18  has a lumen  28  extending its entire length. When the process challenge device  10  is fully assembled, the only path by which a substantial quantity of sterilant can enter the dead end cavity  20  is the path defined by lumen  28 . The length and diameter of the lumen  28  of the challenge tube  18  are selected to present the desired challenge and, more specifically, a challenge commensurate with the most challenging location for sterilant to reach in an actual load to be sterilized. 
     As best shown in  FIGS. 3 and 5 , a biological indicator  30  is positioned within the dead end cavity  20 . The biological indicator  30  shown is self-contained within its own housing  32  which is divided by a wall  34  into two sections  36  and  38 . Section  36  contains a known load of viable microorganisms. Section  38  contains a medium, that when brought into contact with viable microorganisms, will provide an indication of the presence of viable microorganisms. As best shown in  FIG. 3 , the housing  32  of the biological indicator  30  has a port  40  through which sterilant can pass into section  36 . The microorganisms within section  36  will all be deactivated if an adequate quantity of sterilant enters section  36 . This can be determined by rupturing the wall  34 , comingling the medium with the microorganisms, and checking the medium to see if it indicates the presence of any viable microorganisms. The biological indicator  30 , as shown, is only one of many different types of biological indicators which may be used without deviating from the invention. Some suitable biological indicators are self-contained as is indicator  30 , while other suitable biological indicators are not. Depending on the biological indicator employed, the user may incubate the biological indicator after it is subjected to the sterilization process to promote the growth and reproduction of microorganisms surviving the sterilization process being evaluated. 
     Suitable biological indicators  50  are manufactured by various companies. One such biological indicator has a housing containing a disk coated with microorganisms and an ampoule containing a medium which will change color if the ampoule is broken and the medium comes into contact with viable microorganisms. The housing has a filtered opening through which sterilant can enter to deactivate the microorganisms. 
       FIG. 1  also shows a chemical indicator  50  adhered to the outer wall of housing  12 . The chemical indicator may also be coupled to the plug  14 , the access cap  16  or the challenge tube  18 . It may also be positioned within the dead end cavity  20  of the housing  12 . The chemical indicator  50  is selected to react with the sterilant and provide an indication that sterilant has reached the indicator  50  in sufficient quantities to cause such a reaction (e.g., a color change). Thus, the chemical indicator  50  lets a user know whether the process challenge device  10  has been exposed to sterilant or not or, stated otherwise, whether the process challenge device  10  can still be used to, provide a reliable test. The chemical indicator  50  also provides a preliminary indication of the efficacy of the sterilization cycle. If the chemical indicator  50  has not reacted as a result of being subjected to the cycle, the user will know the cycle was ineffective without having to check the biological indicator  30 . 
     The materials used to form the challenge tube  18  and the housing  12  will depend on the sterilant used in the sterilization equipment and protocol being tested. By way of example, when the sterilant is vaporous hydrogen peroxide, the challenge tube  18  and housing  12  are preferably made of materials which are compatible with the hydrogen peroxide. Such materials may include, but are not limited to, low density polyethylene, linear low density polyethylene high density polyethylene, polypropylene, polyethylene terepthalate glycol, polyethylene terepthalate, polyvinyl chloride fluoropolymers, thermoplastics, silicone, stainless steel, aluminum, and glass. 
     As shown by  FIG. 3 , the process challenge device is created by forming an assembly comprising: (1) the housing  12  having a dead end  22 , an open end  24  and an interior cavity  20 ; (2) the biological indicator  30  within the cavity  20 ; (3) the access cap  16  which seals the open end  24  of the housing  12  and has a port  26 ; and (4) a challenge tube  18  having an interior lumen  28  extending the length of the challenge tube  18 , coupled to the port  26  such that the only path by which a substantial quantity of sterilant can enter the cavity  20  is through the path defined by the lumen  28  and the port  26 . The length of that challenge tube  18  and the diameter of the lumen  28  is selected to create a desired challenge. 
       FIG. 3  also shows that the dead end of cavity  20  can be provided by a plug  14 . Sealants, heat, adhesives, gaskets, O-rings, an interference fit, a press fit, or other manufacturing methods can be used to create an acceptable interface between the housing  12  and the plug  14 . These techniques can also be used to form an interface between the cavity  20  and the access cap  16  and the tube  18  and the access cap  16 . As noted above, the plug  14  can be eliminated if the shape of the housing is otherwise fabricated or altered to provide the cavity  20  with a dead end. The tube  18  and access cap  16  can be integrally molded. Likewise, the entire assembly may be integrally molded. 
     As noted above,  FIG. 6  shows the assembly may include sterilization pouch  60 . Sterilization pouch  60  should be constructed of a material which is sufficient to contain the other components and assist in providing the desired challenge. An example of such a material is TYVEK®, a flash spun high density polyethylene fiber. 
     As shown in  FIG. 6 , the sterilization pouch  60  may include a transparent window  62  or may otherwise be made of a transparent material. Likewise, the housing  12  may include a transparent window  64  such that a user can look through the pouch  60  and transparent window  64  into the cavity  20 . This is important if the chemical indicator  50  is positioned within the cavity  20  rather than, for example, attached to the exterior of the housing  12  as shown in  FIG. 1 . Of course, the window  64  can be eliminated if the chemical indicator  50  is positioned as shown in  FIG. 1 , is attached to the exterior of the plug  14 , the access cap  16  or the challenge tube  18 , or is simply placed inside pouch  60 . Likewise, the pouch  60  need not be made of a transparent material or have a transparent window  62  if the chemical indicator  50  is coupled to the exterior of pouch  60 . If the chemical indicator  50  is positioned outside of the housing  12 , the housing  12  need not be made of a transparent material or include a transparent window  64 . 
     When the embodiment shown in  FIG. 6  is employed, the pouch  60  and its contents are placed in a sterilization chamber and subjected to a sterilization process to be tested. The chemical indicator is then checked to determine whether sterilant in sufficient quantities to trigger a response reached the chemical indicator  50 . The assembly comprising housing  12 , access cap  16 , and tube  18  is removed from the pouch  60  and opened by gripping the housing  12  and the flange  17  of access cap  16  to disconnect the access cap  16  from the housing  12 . The biological indicator  30  is removed from the dead end cavity  20 . The biological indicator may then be processed as necessary to determine whether the microorganisms of the biological indicator were deactivated by the sterilization process. 
     The structural and operational features described above provide important advantages. The invention provides a single conduit through which sterilant passes to reach the biological indicator, thus providing an increased challenge for the sterilant to overcome. Substantial quantities of sterilant can only enter the dead end cavity  20  through the tube  18 . The fact that cavity  20  is a dead-end cavity also provides an increased challenge while minimizing the space occupied by the invention. The invention provides flexibility in that it will accommodate the use of a variety of biological indicators, chemical indicators, and sterilants. The invention also provides a challenge device which is inexpensive, easy to manufacture and disposable. 
     Those skilled in the art will appreciate various changes may be made to the embodiments shown and described without deviating from the invention. For example, while the challenge tube  18  is shown as being straight, a curved challenge tube may also be used. The lumen is also shown as having a uniform diameter. The diameter of the lumen can be varied along its length. The pouch  60  need not be used. Other arrangements for coupling the challenge tube  18  to the cavity  20  may be employed. Thus, the invention to be covered is not intended to be limited by the foregoing description, but rather is defined by the following claims.