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Key words: liquid disinfectants, test methods
The Association of Official Analytical Chemists' (AOAC) sporicidal test method for liquid disinfectants specifies the use of porcelain penicylinders and tied loops of 3.0 black, braided suture silk, as "carriers" for dried spores. This test method is used to determine the efficacy of sterilants used in the packaging of medical devices. Certain new formulations of liquid sterilants repeatedly fail the test for silk suture loop carriers, even though they successfully meet the AOAC testing requirements when inoculated penicylinders are used. These formulations pass the test, however, if polyester suture material is used instead of silk. A series of experiments was performed to examine the reasons for this discrepancy.
As supplied from manufacturers, the silk suture is coated with a lubricating wax. To remove this coating, the AOAC method requires an extensive chloroform extraction. Further extraction with 1 N HCl is also specified before the loops are ready for sterilization and inoculation with spores. For these experiments, both polyester and silk suture materials were subjected to this same procedure.
Using B.subtilis (niger ) spores as the test organism, a comparison of the two materials was made to examine the following parameters: 1) the appearance by scanning electron microscopy of both materials before and after extraction with hot chloroform and subsequent treatment with 1N HCl; 2) the elution rates of spores from inoculated, dried loops; and 3) the potential action of loop materials on the sporicidal activity of a chlorine dioxide disinfectant.
Even though chloroform/HCl extraction removed the blue dye from and caused shrinkage of the polyester loops, experimental results suggested that they were similar to silk loops in microscopic appearance, distribution of deposited spores and spore elution characteristics. However, substances present in silk suture loops (or the silk protein itself) caused inactivation of the chlorine dioxide disinfectant. Polyester loops, however, yielded little or no inactivation. OST scientists postulate that during the AOAC test, which does not include agitation of the test assembly, such inactivation can occur in the micro environment of spores situated within the fibers of the braided silk. Subsequently, in the absence of liquid flow, spores are protected by a zone of spent disinfectant. Therefore, polyester suture material is a viable alternative to silk for the AOAC sporicidal test for liquid disinfectants. [PostMS, Stds]
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The barrier research program continues the successful development of laboratory techniques to analyze potential virus transmission risks with condoms and medical/surgical gloves.
Are Condom Breaks More Important than Holes?
Key words: condom, break, hole, risk
Barrier tests of condoms have determined the frequencies with which different types of condoms allow passage of viruses or HIV-sized polystyrene beads and the amount of passage in each case, under exaggerated laboratory conditions.
This information can be used to estimate the passage of semen through holes during actual condom use and to compare that with the potential exposure to semen that results from condom breaks. Table 3 displays summary data from various studies of condom barrier quality determined in OST laboratories. Typically, only a few latex or polyurethane condoms allowed detectable virus passage, while most natural membrane condoms allowed some passage.
Condom material Latex Polyurethane Natural Membrane _____________________________________________________________________________________ Study Lytlea Lytleb Carey Lytlea Lytlea* Carey _____________________________________________________________________________________ Laboratory results # of condoms tested 470 60 89 76 17 20 # of condoms that allowed passage* 12 3 29 4 14 20 Average fluid amount passed per condom tested (mL)* 0.0079 0.0033 0.0016 0.019 0.13 .035 Estimated result in actual use Average semen amount** passed per condom tested (mL) 1.1x10-4 4.6x10-5 2.2x10-5 2.7x10-4 1.8x10-3 4.9x10-4 _____________________________________________________________________________________ * Challenge virus/particles were bacteriophage ØX174 (27 nm diameter) (Lytle et ala,b) or polystyrene beads (110 nm) (Carey et alc). Exaggerated test conditions included low viscosity, high average pressure, and 30 minute test duration. ** Correction factor for semen and actual use conditions, 0.014 (accounting for exaggerated viscosity and average pressure in laboratory test, but not test duration)
For public health risk assessment purposes, it is useful to estimate the average passage of semen per condom. A correction factor is needed to extrapolate from the exaggerated laboratory test conditions (low viscosity and high average pressure) to expected actual use conditions. The calculated estimates of semen passage derived from the different studies are presented in the table.
Condoms that break during use might be expected to allow exposure to the total ejaculate, averaging 3.3 mL of semen (Geigy Scientific Tables). For our comparison, the pooled data available in the public domain indicated a breakage rate for latex condoms of 1.5% (ranging from 0.9% to 1.9%). One study with Tactylon condoms indicated a 1.2% breakage rate. Thus the average semen exposure per latex condom from breakage during intercourse could be 0.05 mL, and for Tactylon condoms, 0.04 mL .
Figure 17 shows the expected average exposures to semen because of breaks or the presence of holes in condoms. The figure indicates that the average exposure to semen from use of latex condoms is greater from breakage (0.05 mL) than from holes (0.00009 mL).
It should be noted that risk is not directly proportional to exposure to a selected volume of semen. Estimation of risk requires further extrapolation because it depends on many variables, especially the infectious agent of interest (particularly its concentration and its probability of causing an infection).
The primary finding of this study was that condom breakage may be more important than holes. Partly as a result of this analysis, the air burst test has been implemented as a second QA test for condoms because it relates to strength (and therefore resistance to breakage).
Condom Test Evaluated with Laser-Drilled Holes
Key words: condom, virus passage, hole, test
The most sensitive test developed to determine whether condoms are effective viral barriers has been evaluated with latex condoms that contained single laser-drilled holes. Virus penetration could be detected through holes as small as 2-3 microns in diameter, even for holes in the reservoir tip. The quantitative results for virus passage through holes of different sizes were roughly consistent with fluid flow through cylindrical holes, i.e., virus passage was proportional to the fourth power of the hole diameter. Previous tests with punctured condoms (having small tears, but not open holes) indicated that small tears in the condom tip may not allow virus penetration. In addition, virus penetration ceased or nearly so within 2 minutes, even for holes as large as 20 microns. Investigations are continuing to determine whether the virus passage cessation may be expected to occur in actual use.
Overall the test was shown to have high sensitivity, high specificity, and low rates of falsenegative and false-positive results. Because of cost, the primary value of this test is in evaluation of condoms made of new materials, rather than as a quality assurance test.
Surfactants Affect Virus Adsorption
Key words: virus, adsorption, surfactant
A mentorship student from Thomas Jefferson High School for Science and Technology, Alexandria, Virginia, investigated the elution of adsorbed viruses with different surfactants. The study demonstrated that adsorption can occur by two basic interactions, ionic and nonionic, and that complete recovery of the virus was possible, i.e., adsorption was not irreversible, with the appropriate choice of surfactant. These results form the foundation for understanding and optimizing barrier tests of medical devices and for optimizing disinfection processes where microorganisms may be adsorbed to various medical devices.
Barrier Tests of Guayule as Substitute for Natural Rubber Latex
Key words: guayule latex, barrier, glove, condom
The U.S. Department of Agriculture is developing a new type of natural, hypoallergenic latex from the guayule shrub, Parthenium Argentatum Gray, which grows in the U.S. Southwest. Handdipped prototype gloves and condoms have been made from purified guayule latex and were tested for barrier qualities in an OST lab. Although most of the prototype gloves displayed manufacturing defects as evidence by water leakage in the 1000 ml water leak test, the fingers that passed the water leak test were effective barriers to a small challenge virus. Guayule latex areas free of manufacturing defects were comparable as barriers to gloves made of natural rubber latex or nitrile. In addition, when tested by the ASTM F16 70-95 test as a barrier to artificial blood, material from the prototype condoms was also shown to be an effective barrier. Thus, while manufacturing defects in the prototype products were common, these tests demonstrated that the basic guayule latex material, free of defects, was effective as a barrier material. The guayule latex could replace natural rubber latex for individuals who are allergic to the current products.
Sterility Assurance Levels (SAL)
Key words: infection, sutures, staphylococcus
A project to determine the adequacy of sterility assurance levels (SAL) was undertaken. The specific scientific question asked was how many organisms does it take to cause an infection, or what is the infection rate with low numbers of organisms on an implanted device? With the data obtained, a risk analysis assessment could be undertaken to determine the impact on infection risk if the SAL were changed so that as many as 1/1000 items in a sterilization procedure could be nonsterile rather than the 1/1,000,000 which is the current standard. Infection risks with two organisms and seven materials using a mouse model were determined. The infection risk with between 10 and 20 organisms is approximately 30%. The infection risk with less than 10 organisms is approximately 6%. The data are being evaluated by ODE for consideration of a different SAL for materials that undergo degradation with the more intensive sterilization procedures.
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Key words: liquid disinfectants, chemical disinfectants, sterilize
The risk of hospital-based infections by bacteria and other pathogens, including HIV, is increased by multiple use of inappropriately sterilized medical devices. The goal of this project is to evaluate the relative effectiveness of glutaraldehyde, chlorine, peracetic acid, formaldehyde, peroxide, metal-based formulations, and phenolics against bacterial spores, vegetative bacteria and viruses, including HIV, that are known to contaminate medical devices. Representative test materials include a corrodible material (carbon steel), a noncorrodible material (a metal-grade titanium alloy), and a synthetic polymer (medical silicone rubber).
Quantitative methods were developed to measure contamination of medical devices and to assess sporicidal, bacteriocidal, and virucidal activity of liquid disinfectants. Thirteen common pathogenic bacterial species were ranked according to their relative resistance to a panel of disinfectants commonly used to decontaminate medical devices. The relative cellular toxicity of liquid disinfectants was studied by an AOAC standard method. A variety of cell lines, including human cells, were studied. To overcome perceived deficiencies in the AOAC standard method, improved quantitative techniques were developed. These results have provided CDRH with a scientific basis for assessing the relative effectiveness of chemical disinfectants commonly used to test medical devices. [PreME, ProA]