Viewpoint: Using irradiation to treat PPE
"Irradiation technologies are used to sterilise almost half of the global supply of single-use medical products. Sterilisation using irradiation, mainly gamma, began in earnest in the 1950s to eliminate microorganisms, such as bacteria, viruses, fungi and spores, from medical equipment. Currently, almost 50% of healthcare products, such as gloves, syringes and single-use medical products and devices, are sterilised using gamma rays, electron-beams or X-rays prior to use.
Since inception, radiation processing, mainly using a cobalt-60 source to deliver gamma radiation, has remained a vital technology that has expanded as demand for healthcare and for sterile products has grown. Reusable surgical equipment is mainly processed using autoclaves located at or proximate to hospitals and clinics. Such equipment includes surgical instruments, gowns and drapes.
Single-use medical equipment and associated products are sterilised in order to protect patients from infection during operations and invasive procedures. In contrast, PPE is designed to protect the wearer from risks encountered in performing their duties. Understanding the difference in the purpose and use of products is important when considering how to expand supply and availability though increases in manufacturing capacity or by enabling products to be reused.
In order to re-use PPE, it is necessary to remove or to render harmless any COVID-19 contamination, thereby making the equipment safe for re-use. It is also necessary to determine the maximum level of potential contamination so that a standard irradiation dose can be calculated that renders the product safe. It will then be important to understand if the required irradiation dose has any adverse effect on the integrity or functionality of the product being processed.
The sterilisation of single-use medical devices and products using gamma irradiation is an extremely well-established process which is supported by a wealth of technical data relating to material compatibility. Comprehensive regulations have been established to ensure that products meet the desired sterility assurance requirements and performance characteristics.
The sterilisation of re-usable equipment is usually performed at or proximate to hospitals, whilst terminal sterilisation by irradiation is usually undertaken at large processing sites near points of manufacture or at major transport hubs or intersections. The logistical challenges associated with the collection, processing and redistribution of contaminated PPE from hospitals and clinics should not be under-estimated when considering the practical aspects of reprocessing.
Industrial irradiation facilities are well used to handling products of different dimensions and densities, each requiring different irradiation doses. The possibility of introducing contaminated materials to an existing operational facility presents many risks and challenges that previously have not existed, and which will require careful consideration before processing can commence.
As the impact of the Novel Coronavirus crisis in China began to be recognised in January and February 2020 there was a sudden huge surge in demand for protective garments, later replicated around the world. In China the State Council allowed protective clothing to be processed using irradiation as an alternative to ethylene oxide.
Materials processed using irradiation are available for use soon after processing whilst ethylene oxide requires a post process quarantine period of between 7 and 14 days. As well as increasing operational capacity, the ability to use irradiation increased the available supply by accelerating the point at which materials could be used. The initiative was promoted by the China Isotope and Radiation Association and actively implemented by companies such as China Isotope and Radiation Corporation, which is part of China National Nuclear Corporation.
As the criticality of COVID-19 became increasingly clear, organisations such as Nelson Laboratories, a leading global supplier of laboratory testing, began to undertake research. Other studies were initiated including a study by Massachusetts Institute of Technology (MIT) and others in the USA. This highlighted the challenges associated with reprocessing of PPE.
The MIT study acknowledged that there was significant literature that supports viral inactivation of SARS-CoV at doses of 10 kGy, but when repeated it was found that the filtration efficiency of the masks was degraded even at 10 kGy. In normal circumstances, PPE is disposable so much remains unknown about the efficacy and impact of various sterilisation systems on disposable masks and PPE. There is a lack of research as there has been an absence of need because these products and materials have been disposable, so reprocessing has not been fully evaluated.
In recent days, the International Atomic Energy Agency (IAEA) has reported that radiation has been found to be effective in sterilising PPE except for respiratory masks. The recommendation is to use radiation prior to use, which suggests using it to process new products. The IAEA has also recently reviewed the findings from five institutions that have undertaken research to test the impact of ionising radiation, gamma and electron beams, when used to sterilise used respiratory masks, including models such as N95 and FFP2, which are commonly worn by medical personnel. Given the COVID-19 transmission risk, face masks are especially important to both healthcare workers and the general public.
The World Health Organisation has recommended the use of FFP2 grade (N95/KN95) masks during outbreaks of SARS, Avian Flu and COVID-19 as these masks filter out 95% of external airborne particles and protect users from liquid contaminating the face. These masks differ from surgical masks, which for the most part only guard others against the wearer’s own respiratory output.
The IAEA’s review of recent research carried out by institutes in France, Israel, Poland, South Korea and the USA has indicated that the radiation dose required to sterilise - or render the COVID-19 virus inactive and hence safe - results in a decrease in mask filtering capability and performance. In these studies, masks were exposed to 24 kGy of radiation, significantly higher than the 10 kGy referenced above. Whilst there were no reported structural changes in the masks the filtering capability was shown to be significantly reduced. The tests were performed using a mixture of gamma and electron beam irradiation.
The irradiation industry provides a vital service in the provision of sterile single-use medical devices. It is global in its reach, collaborative in its approach and dynamic in its willingness to embrace new scientific discoveries or market needs. However, the industry recognises that there is no one-size-fits-all solution to problems and it supports the use of alternative technologies where these provide enhanced solutions.
The irradiation community includes nuclear power operators, manufacturers and suppliers of Cobalt-60 and accelerator technology, contract irradiation facilities, support services, medical device manufacturers, institutes and universities."
Paul Wynne
A recognised NGO of the IAEA, the International Irradiation Association promotes the safe and beneficial use of irradiation technologies. The association has a diverse international membership with strong links to regional and specialist groups and associations.
