Special Issue on Plasma Sterilization and Decontamination

More than 50 million surgical and invasive medical procedures—including approximately 5 million gastrointestinal endoscopies—are performed each year in the US alone. During these procedures, the close contact between surgical instruments and the exposed tissues of the patient can constitute an additional health risk due to the increased possibility of contamination by pathogens introduced by the surgical device itself: if the instruments used are not properly disinfected or sterilized, the risks of transmission of infection from person-to-person (e.g., hepatitis B virus) or of introducing environmental pathogens (e.g., Pseudomonas aeruginosa) become high. The seriousness of this problem can be clearly seen by considering that the number of Hospital Acquired Infections (HAI) is estimated to be of the order of 2 million each year in the US. Moreover, the number of these infections which, directly or indirectly, may be linked with patient death in U.S. hospitals is thought to have been about 10 000 in 20021 for a cost of the order of 5–7 b$. Similar figures are also reported for the UK and France, with 100 000 HAI leading to about 5 000 deaths in 2000 for UK2 and 4 000 for France.3 These alarming figures are also reflected in the statistics of other European countries and serve to underline the importance of developing and applying robust sterilization and decontamination processes and procedures. Recent studies in the UK have shown that significant quantities of residues composed of salts, proteins and undefined organic matter can remain on surgical instruments even after applying the normal cleaning and sterilization procedures adopted in Sterile Service Departments.4 These observations raise serious concerns since it shows that prion protein, responsible for the different variants of the Creutzfeld Jacob Disease (CJD), could potentially be transmitted iatrogenically by contaminated instruments. Finally, possible contamination by pyrogens (fever inducing substances) coming from Gram-negative bacteria [lipopolysaccharides (LPS)] or Gram-positive bacteria [lipoteichoic acid (LTA), peptidoglycan (PGN)] is also linked to these residues. Pyrogens, or bacterial endotoxins, can—at elevated doses—cause sepsis when in contact with the patient bloodstream and provoke septic shock, a major cause of death among hospitalized patients. The potential risk from these residues is further exasperated by their high resistance to temperature and the inability of conventional sterilization procedures to remove or inactivate them. The reduction or avoidance of these problems can only be achieved by developing and implementing methods of decontamination and sterilization which ensure complete removal of bacteria, pyrogens and proteins. The sterilization operations must follow strict rules such as the ones described in the norm ISO EN 15883 or NICE guidelines IP196. The instruments are placed in a mechanical washer/disinfector and are subjected to a pre-wash at room temperature to prevent blood coagulation and adhesion of proteins. They are then cleaned and sonicated with an alkaline enzymatic detergent, and finally high temperature washed and rinsed. They are then visually inspected after drying and packaged for sterilization (in most cases by autoclaving). Obviously, these operations are not efficient in removing strongly adhering organic residues and the use of non-equilibrium plasma discharges has been proposed as a possible solution: plasma processes are able to remove organic material (such as photoresist in the microelectronics industries) with high efficiency, while working at low temperature and using gases which present little or no risk due to toxicity. Indeed, it has been shown that many pathogens can be destroyed employing non-equilibrium plasma discharges5-7 and the nature of plasma interactions with microorganisms or biomolecules has been extensively studied. The pioneering work done, for instance, at Université de Montréal showed the complexity of mechanisms operating during the deactivation of bacterial spores. This area of study, however, remains very challenging to understand and optimize due to the numerous ways in which the high fluxes of the various neutral and ionized active species as well as energetic photons in plasma discharges can interact with the biological systems being treated. In the present Special Issue, we aim to publish articles presenting the current trends and developments in the field of plasma sterilization and decontamination. Topics covered will include mechanistic studies with low pressure to atmospheric pressure plasmas, source and reactor configurations, process development and applications, as well as one full-scale industrial process development in the pharmaceutical field. These articles will provide an interesting and valuable insight into the mechanisms by which plasma discharges interact with contaminants, opening the way to large scale applications in both the medical device area and pharmaceutical industries. We, the editors, would like to thank all the authors for their contributions and the reviewers for providing quick feedback on the articles submitted. We would like also to thank the Managing Editor Dr. Renate Förch, for helping us in the coordination of this edition. Guest Editors: François Rossi Michel Moisan Michael Kong Mounir Laroussi