Effective ultraviolet C light disinfection of respirators demonstrated in challenges with Geobacillus stearothermophilus spores and SARS-CoV-2 virus.

BACKGROUND: The global COVID-19 pandemic, accompanied by spikes in the number of patients in hospitals, required substantial amounts of respiratory protective devices (respirators), thereby causing shortages. Disinfection of used respirators by applying ultraviolet C (UVC) light may enable safe reuse, reducing shortages. AIM: To determine whether UVC disinfection is applicable to enable repeated safe reuse of respirators. METHODS: The UVC chamber, equipped with low-pressure mercury discharge lamps emitting at 254 nm, was used to determine the sporicidal and virucidal effects. Respirators challenged with spores and viruses were exposed to various UVC energy levels. Deactivation of the biological agents was studied as well as UVC effects on particle filtration properties and respirator fit. FINDINGS: A 5 log10 reduction of G. thermophilus spore viability by a UVC dose of 1.1 J/cm2 was observed. By simulating spores present in the middle of the respirators, a 5 log10 reduction was achieved at a UVC dose of 10 J/cm2. SARS-CoV-2 viruses were inactivated by 4 log10 upon exposure to 19.5 mJ/cm2 UVC. In case UVC must be transmitted through all layers of the respirators to reach the spores and virus, a reduction of >5 log10 was achieved using a UVC dose of 10 J/cm2. Exposure to a six-times higher UVC dose did not significantly affect the integrity of the fit nor aerosol filtering capacity of the respirator. CONCLUSION: UVC was shown to be a mild and effective way of respirator disinfection allowing for reuse of the UVC-treated respirators.

A survey to quantify wet loads after steam sterilization processes in healthcare facilities.

Wet loads after steam sterilization of medical devices in healthcare facilities are unacceptable. However, little is known about their frequency in daily practice. An online survey was distributed via four national sterilization associations, in Australia (Sterilising Research Advisory Council of Australia (Vic), Inc. (VIC SRACA)), Belgium (Vereniging sterilisatie in het ziekenhuis (VSZ)), Italy (Associazione Italiana Operatori Sanitari addetti alla Sterilizzazione - Società Scientifica (AIOS)), and The Netherlands (Vereniging van Deskundigen Steriele Medische Hulpmiddelen (VDSMH)). Seventy-eight percent of 125 hospital sterilization facilities recognized wet loads, occurring at frequencies ranging from monthly to every load. Usually, wet loads were identified by the presence of water droplets; these loads were repacked and resterilized. Given the pervasiveness of wet loads, and their impact on reprocessing times and costs, strategies to reduce their frequency are needed.

Measuring non-condensable gases in steam.

In surgery, medical devices that are used should be sterilized. To obtain surface steam sterilization conditions, not only in the sterilizer chamber itself but also in the loads to be sterilized, the amount of non-condensable gases (NCGs), for instance air, should be very low. Even rather small fractions of NCGs (below 1%) seriously hamper steam penetration in porous materials or devices with hollow channels (e.g., endoscopes). A recently developed instrument which might detect the presence of residual NCGs in a reliable and reproducible way is the 3M(TM) Electronic Test System (ETS). In this paper, a physical model is presented that describes the behavior of this instrument. This model has been validated by experiments in which known fractions of NCGs were introduced in a sterilizer chamber in which an ETS was placed. Despite several approximations made in the model, a good agreement is found between the model predictions and the experimental results. The basic principle of the ETS, measuring the heat transfer by condensation on a cooled surface, permits a very sensitive detection of NCGs in harsh environments like water vapor at high temperatures and pressures. Our model may serve to develop adapted and optimized versions of this instrument for use outside the field of sterilization, e.g., in heat exchangers based on steam condensation.

Temperature dependence of F-, D- and z-values used in steam sterilization processes.

AIMS: To develop a model, based on microbiological principles, to safely optimize steam sterilization processes. METHODS AND RESULTS: The minimum exposure time F for a decontamination process at a certain temperature is usually calculated from an empirical model with the decimal reduction time D and the temperature resistance coefficient z as parameters. These are implicitly assumed to be independent of temperature. Using a microbiological approach, it is shown that also D and z depend on temperature, indicating that the usual models provide only reliable results in a limited temperature region. The temperature dependence of F resulting from this approach describes the available experimental data very well. Safety margins to assure sterility can be included in a straightforward way. CONCLUSIONS: The results from the present approach can be used to safely optimize decontamination processes. The corresponding mathematical model can be implemented rather directly in process control systems. SIGNIFICANCE AND IMPACT OF THE STUDY: Our results show that for steam sterilization and disinfection processes the values of F predicted by the usual models largely underestimate the required minimum exposure times at temperatures below 120 degrees C. This has important consequences for the optimization of such processes.

A validation survey of 197 hospital steam sterilizers in The Netherlands in 2001 and 2002.

Steam sterilization is the most common method of sterilization used in hospitals and by companies sterilizing for hospitals. This study validated 197 steam sterilizers with respect to technical condition, various production processes and routine control tests, according to the European norms and standards for steam sterilization. Overall, only 40% of the validated steam sterilizers met the norms and standards. We recommend that adequate measures need to be taken, based on the comments in the validation reports, in order to guarantee the sterility of processed medical items.