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Key words: computational fluid dynamics, barrier devices, modeling, tech support, research
Synthetic barriers such as gloves, condoms, and masks are widely used in efforts to prevent disease transmission. Virus penetration tests are used to evaluate barrier effectiveness. Questions remain, however. For example, what is the probability of transmission of a more hazardous virus? Or, what is the likelihood of transmission under more realistic conditions? Or, when do penetration tests underestimate the risk associated with the use of a given barrier? An understanding of how a virus is transported through passageways in a barrier would be invaluable in accurately assessing the risk associated with barrier use. Unfortunately, experimental investigations involving such passageways are difficult to perform, owing to the small dimensions involved.
OST researchers have consequently developed a mathematical model for analyzing and predicting virus transport through barriers. The model incorporates a mathematical description of the parameters associated with virus transport, including carrier fluid flow (blood, semen, saline, etc.), random thermal motion, and virus/barrier interaction forces. The critical element of the model is an empirically derived "rate constant" characterizing the interaction force between the virus and the barrier. Once the model has been calibrated by specifying the rate constant, it can predict virus concentration throughout a barrier pore under a wide variety of conditions.
The rate constants for four bacterial viruses interacting with latex in a saline medium have been determined by using an apparatus that employed a virus suspension flowing between two closely spaced latex sheets. The model was further tested using laser-drilled pores in condoms by comparing the measured amount of virus transmission with the model's prediction. Model predictions agreed well with measured values (figure 15).
Figure 15 - Comparison of Measured Viral Transmission Using Laser-Drilled
Pores
The model was then used to compute the amount of virus transmitted through a cylindrical pore under the test parameters used in FDA membrane tests. For the four bacterial viruses considered, results revealed that barrier integrity tests can significantly underestimate the risk associated with barrier use.
One important future use of the model will be to convert risk assessments based upon a test virus to predictions based upon the actual virus of interest. Efforts are underway to calibrate the model for viruses of great public-health importance, including herpes and HIV, and to perform transmission calculations using realistic pore geometries, such as slits and tortuous paths.