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New test methods are needed for medical textiles

December 1st, 2019 / By: / Advanced Textiles, Markets

by Matthew Hardwick, ph.D.

The spread of infection is a concern for all of us, but nowhere is it more concerning than in health care. The spread of infection both to and from medical environments is an ever-present problem in hospitals and clinics around the world. Numerous resources are being dedicated to fight the war against hospital-acquired infections. Health-care textiles, including scrubs, lab coats and linens, are at the front line of this war against infected body fluids and the spread of disease. 

Health-care workers, primarily nurses, are in constant contact with many patients throughout the day, but they rarely change their scrubs—generally only when visibly soiled. Therefore, they may become a walking source of infectious material. Patient beds, sheets and blankets are changed frequently, but may spread pathogens through the air during changing, or through contact with other linens and equipment. Even privacy curtains present a danger for the spread of infections. 

In health-care settings, textiles can act as mobile vectors of infectious microorganisms, or microbes. There is disagreement about how effective microbe-reducing textiles are at actually combating the spread of microbes. This controversy partially stems from how the antimicrobial efficacy of textiles is determined and how that translates to the medical world. Photo: Dreamstime.

Professionals in the textile world understand the potential role of textiles in preventing the spread of infections. Antimicrobial active ingredients such as copper, silver, zinc and quaternary ammoniums have been added to a variety of textiles in order to reduce microbial contamination of health-care textiles. Further, other agents such as chlorine-binding and hydrophobic (fluid-resistant) chemistries have been added to these textiles to reduce the problem. 

In health care, there is little question that textiles act as mobile vectors of infectious microorganisms, or microbes; however, there is considerable controversy about how effective microbe-reducing textiles are at actually combating the spread of microbes. This controversy stems from how we determine antimicrobial efficacy of textiles and how that translates to the medical world. 

Antibacterial textile testing

The first topic to address is the difference between “antibacterial” and “antimicrobial.” Antimicrobial implies that a technology works against all microbes, including bacteria and fungi (and viruses to a lesser extent). Much of the testing performed on “antimicrobial” textiles in health care is actually antibacterial. While fungi, such as Candida species, are an important concern in health care, bacterial species, such as Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), are far more prevalent. 

Although I have used antimicrobial to describe these chemistries (indeed, they are generally effective against bacteria and fungi, and viruses, in some instances), health-care textiles are generally tested for efficacy against bacteria, so references about health-care textile testing will be concerning antibacterial properties and will limit testing options only to testing antibacterial chemistries.

Testing laboratories have several means to test antibacterial textiles. In the United States, the American Association of Textile Chemists and Colorists (AATCC) and American Society for Testing and Materials (ASTM) have developed antibacterial textile tests. Internationally, there are several additional tests available.

The tests do a great job at describing the capacity of an antibacterial textile to either prevent bacterial growth or kill the specified bacteria. These methods are excellent for refining the antibacterial formulation in a textile product during development and for determining the quality of antibacterial application during production. However, they fall short in determining efficacy on bacteria in the real world.

Current methods 

While each of the established test methods serves an important role in the development of effective antibacterial textiles, they are inadequate with regards to the medical community, largely due to the conditions of the methods. With the exception ASTM E 2149, each of these tests has a 24-hour contact time between a liquid bacterial inoculum and the treated textile. 

Essentially, the textile is kept in a humid chamber with the bacteria. While humid conditions are critical for the bacteria (they will die in a dry environment) and a 24-hour period is needed to see adequate growth of the bacteria on an untreated textile, these conditions do not represent real life for a medical textile, such as a typical scrub suit (unless it’s at the bottom of a hamper). 

With ASTM E 2149, the testing conditions are even more convoluted. Because this method was developed for hydrophobic textiles, like those treated with quaternary silanes, the liquid bacterial inoculum must be in constant and vigorous contact with a treated textile. Therefore, a greater inoculum volume is used and the system is shaken over the course of an hour using a wrist-action shaker—something clothing will not likely experience in the course of a day. But it was intended as a fast quality assurance test method.  

Indeed, there is still controversy with regards to clinical evidence for antibacterial efficacy of treated textiles. The lack of a solid connection between laboratory data and clinical performance may be due to the nature of the test methods described. Clinical trials, much like field wear trials, are complicated tasks involving many people, and so can be very expensive and time consuming. 

What is needed

The industry needs test methods that bridge the gap between the basic test methods currently available and arduous and expensive clinical trials. The Expert Group on Efficacy of Biocide Treated Articles within the Organization for Economic Cooperation and Development, Task Force on Biocides recommends a three-tiered approach to determining efficacy of antibacterial treated articles.

  • Tier 1: Proof of Principle defines the basic industry standard tests that determine efficacy of an antibacterial treated article in a controlled laboratory environment.
  • Tier 2: Simulated Use defines the translational tests that mimic end-use scenarios, environments and incubation times.
  • Tier 3: In-Use Evaluation substantiates direct health benefit claims or supports marketing initiatives by the development of clinical trials that take place in end-use environments under real-world conditions.

The current standard test methods fit the Tier 1 category. Clearly, clinical trials fall into Tier 3 testing. What’s missing are Tier 2 test methods for medical textiles. These should be laboratory-based and predictive of eventual clinical trials. Such an approach will, in the end, save the industry considerable time and money. 

ResInnova Laboratories LLC is pioneering Tier 2 testing in the medical textile field. The company has developed the fabric challenge assays in response to this lack of predictive testing in the antibacterial textile field. These assays introduce microbes to textile swatches via aerosol, direct contact and splatter inoculation, mimicking how medical textiles become contaminated in real life. 

The assays have the ability to differentiate products based on how they perform against each of the three inoculation techniques. Moreover, the results, especially for the splatter assay, are predictive of clinical trial performance. 

A path forward

Because very little has changed in testing since the original methods were developed, the link between effectiveness shown with these methods run in the laboratory and real-world efficacy is simply inadequate. The tiered approach to testing should guide the industry as it moves forward into newer industries, such as the medical field, where scrutiny and regulation are more stringent.

While ResInnova Laboratories has developed a series of methods, the fabric challenge assays, they have not become standards. It is time for the industry to rise to this challenge and bring forward a new era of antibacterial testing. 

Matthew Hardwick, Ph.D., is president and CEO of ResInnova Laboratories, Silver Spring, Md. The company offers a range of services to help clients’ facilities improve environmental cleaning. ResInnova’s laboratory tests products that reduce pathogens on environmental surfaces, including textiles. For more information, visit www.resinnovalabs.com