Nosocomial infections represent the most frequent adverse event for patients during hospital stays, and they threaten the quality of patient care. Removing pathogens from inanimate surfaces could be a useful and helpful complement to conventional hygiene measures.
Patients are usually admitted to hospitals for treatment of afflictions or to improve their quality of life. But what happens when instead of being cured and recovering, they acquire new infections that prolong their suffering? A healthcare-associated infection (HAI) is defined by the WHO as “an infection occurring in a patient during the process of care in a hospital or other healthcare facility, which was not present or incubating at the time of admission1“.
HAIs represent a significant clinical challenge and pose a serious risk to the quality of patient care and the safety of patients. Moreover, they cause significant costs for the healthcare systems with an estimated burden of EUR 7 billion per year in Europe2, over four million people are affected by HAIs every year in the EU3. In Germany, approximately 6% of the annual 400,000 to 600,000 HAIs are caused by multi-resistant pathogens, as shown by data collected by the German nosocomial infection surveillance system KISS, which allows an accurate monitoring of such infections4.
The most important interventions for addressing HAIs are hand hygiene, strict infection control monitoring, and cleaning regimens. Also, reducing contamination of inanimate surfaces by nosocomial pathogens could help prevent HAIs5. “It is important to note that 80% of HAIs are caused by endogenous pathogens, which permanently live in the human body,” explains Prof. Cornelia Lass-Flörl from the Medical University of Innsbruck, Austria, director of the Division for Hygiene and Medical Microbiology. “They colonise the skin and the gastrointestinal tract, and can enter the patient’s body during operations or by moving along catheters. Exogenous pathogens that come from the environment cause 20% of HAIs. Those are the infections that could be avoided by reducing surface contamination. Yet at the moment there are no clear clinical data proving a correlation between environmental surface contamination and incidence of HAIs.” Researchers are still working on this.
Antimicrobial coatings are designed to reduce microbial contamination of surfaces in healthcare facility settings. They represent a possible means to help reduce the transmission of dangerous pathogens in hospitals by supplementing standard infection prevention strategies6. Pathogens such as Clostridium difficile spores, vancomycin-resistant Enterococcus (VRE), methicillin-resistant Staphylococcus aureus (MRSA), Acinetobacter baumannii and Norovirus can attach to surfaces, form a biofilm layer, and survive for days and even months7.
Healthcare workers’ hands can touch contaminated surfaces such as door and window handles or light switches during patient care, which increases the risk of pathogen transmission. “Patients in intensive-care units are most likely to acquire HAIs,” explains Lass-Flörl. “These patients usually have a central venous access, a urinary catheter, and are intubated. Such devices represent a bridge from the outside environment into the body. Pathogens, mostly resistant microbes, can migrate along these catheters to the blood, the bladder or the lungs and can then cause infections.”
Currently, numerous efforts are underway for developing new antimicrobial surface coatings. Antimicrobial coatings need to resist disinfection agents used in daily cleaning procedures and, at the same time, should not cause resistance. Moreover, they should be effective against bacteria, viruses, and fungi, but show no toxicity. Whereas certain materials prevent the physical attachment of pathogens to the surface, other materials chemically kill microbes that are already on the surface.
Understanding microbe-material interactions is crucial for implementing new surfaces such as nanorough titanium surfaces, which significantly reduce microbial adhesion8. Polyethylene glycol (PEG)-coated surfaces, diamond-like carbon (DLC) films or polymers are other innovative approaches for preventing pathogen attachment to surfaces. However, all these surfaces lack biocidal capacities.
Alternatively, antimicrobial compounds including copper, silver, silanes, antibiotics, and triclosan can be added to coatings to eliminate pathogens on surfaces. Copper is well known to have antimicrobial properties, and its efficacy has been demonstrated in several investigations. Copper weakens the membrane of bacteria, which allows copper ions to enter the bacteria and prevent their proliferation. Copper-coated surfaces harbour 90% fewer bacteria than conventional surfaces9. To date, copper is the only material with proven antimicrobial activity in the clinical setting.10
“The commercial offering of antimicrobial effective substances is very broad. However, there are very few surfaces that show long-lasting antimicrobial efficacy under real-life conditions,” remarks Lass-Flörl. “Companies often test their products according to the Japanese Industrial Standard (JIS), which does not represent the clinical setting, as humidity and temperature are much higher than in real life. We have been able to observe a limited antimicrobial effect when antimicrobially coated surfaces undergo cleaning or disinfection. These limitations represent a real problem when evaluating the influence of antimicrobial coatings on the incidence of HAIs.”11
Besides the lack of standardised testing methods, the absence of technical specifications, hygiene requirements, and clinical guidelines all hinder the use of antimicrobial coatings in healthcare facilities. More studies on healthcare decontamination are required to provide new evidence on the role of antimicrobial surfaces for infection prevention and for targeting multi-resistant pathogens. “Despite the current obstacles that still need to be overcome, it is definitely worth continuing to do research in this direction, as this approach is very attractive,” Lass-Flörl concludes.