INFECTION CONTROL


Comparative Testing of Agents Used to Disinfect/Sterilize Medical Devices

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 included 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. Results have shown that the effectiveness of a given disinfectant depends on treatment conditions, such as pH and temperature, as well as the nature of the device material. These results provide CDRH with a scientific basis for assessing the relative effectiveness of chemical disinfectants commonly used to test medical devices. [PreME, ProA]

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Condoms as Virus Barriers: Determination of Base-Line Properties and Evaluation of Quality Assurance Tests

Key words: condoms, virus penetration, air burst test, sensitivity

This project provided information needed in the evaluation and regulation of condoms and had two primary goals. The first goal was to determine the baseline level of marketed latex male condoms that allow virus penetration and the amounts of penetration. The second goal was to evaluate a quality assurance test, the air burst test, with regard to detecting defective condoms that can allow virus penetration.

The proportion of condoms that allowed some level of virus penetration was determined, with lubricated condoms being as effective virus barriers as unlubricated ones. These data represent the baseline virus barrier qualities of off-the-shelf latex condoms against which all new condoms will be compared, for future ODE evaluations. In addition, the Atlanta regional lab is now ready to use the virus penetration test for regulatory purposes and may adopt our laboratory test as a standard field test to support future compliance actions.

The air burst test (done at the Winchester Engineering Analytical Center [WEAC] did not detect small tears in the condom tip, although it could detect those in the shaft section of the condom. The virus penetration test was also less able to detect such defects in the same location. Further, it was found that virus absorption limits the sensitivity of the virus penetration test and that increasing the duration of the virus penetration test will not increase its sensitivity.

Given the limited abilities of these tests to detect holes in the tips of condoms (i.e., the "business" end), it is important to develop a more sensitive, reliable test for detecting such holes. This information has utility for both device evaluation (510[k]s and PMAs) and for quality assurance in the field. [PreME, Enf, ProA]

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Condom Leakage Test Methods

Key words: condoms, test methods, leakage

In collaboration with WEAC, OST is testing a variety of condom devices, including polyurethane female condoms, latex male condoms, and polyurethane male condoms, to determine appropriate test methods for each device. In particular, an air leak test, a viral challenge test, and a water leak test have been evaluated for testing the female condom.

One set of female condoms with holes produced by an excimer laser was tested first with a nondestructive differential air deflation test. The air deflation test is a new test adapted from one developed by OST to evaluate surgeons' gloves. Each test condom and a control condom were inflated to about 70 mmHg air pressure, and then the pressure difference between them was monitored for 1 minute. The rate of change in pressure can be directly related to hole size by comparison to pressure changes induced by standardized holes in nickel foil. The results for 22 condoms is shown in figure 13. The air deflation test performed very well for 20 µm holes but did less well at quantifying the smaller holes although some of the observed variation may be due to variation in actual hole size.


Figure 13 - Test results for the reality female condom

Results for an air deflation test of the Reality female condom. All 22 condoms has laser fabricated holes. The test was highly effective in finding and in quantifying the size of the larger holes.


A second test protocol, similar to the one used to test male condoms as virus barriers, was used on the same set of condoms. The basic test consisted of filling the condom with a challenge virus suspension, pressurizing the condom, submerging it in a buffer for 30 minutes to collect any virus that might penetrate the condom, and assaying the collection buffer to determine how much virus penetrated the condom. An open-mesh restrainer was used to prevent the condom from expanding under pressure. All laser-produced holes allowed virus penetration in this test. Seven 10 µm holes allowed a mean penetration of 3x10-3 mL (range = 2x10-2 to 9x10-5 mL). Nine 20 µm holes allowed a mean penetration of 1.5x10-1 mL (range = 7x10-1 to 3x10-3 mL). Samples were also removed from the collection buffer at intermediate times and indicated that virus penetration often was complete by 10 minutes, even for 20 µm holes. The reason that viral penetration did not continue for 30 minutes is not known, but the data suggest that the hole in the condom closed or was blocked.

Thus, the virus penetration test can detect holes in the female condom as small as 10 µm (and possibly smaller); but, because the rate of virus penetration usually decreased with time and was variable from one condom to another, the amount of virus penetration provides only an estimate of the effective hole size. While this test can reliably detect smaller holes than either the air deflation test or the water leak test used for quality assurance, it is too costly and slow to be used for quality assurance. The virus penetration test is however, useful for the type of qualifying tests used for 510(k)s and PMAs.

OST also assisted WEAC in the development of new water leak tests to find pinholes in polyurethane female condoms. Techniques were successfully developed and are now in use to evaluate manufactured condoms. Further, in regard to male condoms, an electron beam technique may prove to be faster and more accurate than any other test. Such a system has been installed and calibrated for polyurethane male condoms. Initial evaluations of this new test method have begun [PreME, PostMS, Stds]


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