The effectiveness of treating irrigation water using ultraviolet radiation or sulphuric acid fertilizer for reducing generic Escherichia coli on fresh produce-a controlled intervention trial.

AIMS: The aims of this study were to: (i) estimate the effectiveness of ultraviolet radiation (UV) and sulphuric acid-based fertilizer (SA), at reducing levels of generic Escherichia coli in surface irrigation water and on produce and surface soil in open produce fields; and (ii) describe the population dynamics of generic E. coli in produce fields. METHODS AND RESULTS: Spinach and cantaloupe plots were randomly assigned to control, UV or SA treatment groups. Irrigation water was inoculated with Rifampicin-resistant E. coli prior to treatment. More than 75% of UV- and SA-treated tank water samples had counts below the detection limit, compared to a mean count of 3·3 Log10 CFU per ml before treatment. Levels of Rifampicin-resistant E. coli in soil and produce both increased and decreased over 10-15 days after irrigation, depending on the plot and time-period. CONCLUSIONS: UV and SA treatments effectively reduce the levels of E. coli in surface irrigation water. Their effectiveness at reducing contamination on produce was dependent on environmental conditions. Applying wait-times after irrigation and prior to harvest is not a reliable means of mitigating against contaminated produce. SIGNIFICANCE AND IMPACT OF THE STUDY: The results are of timely importance for the agricultural industry as new FSMA guidelines require producers to demonstrate a low microbial load in irrigation water or allow producers to apply a wait-time to mitigate the risk of contaminated produce.

Decontamination of SARS-CoV-2 contaminated N95 filtering facepiece respirators using artificial sun lamps.

AIMS: Assess the feasibility of using light from artificial sun lamps to decontaminate N95 filtering facepiece respirators (FFRs) contaminated with SARS-CoV-2. METHODS AND RESULTS: FFR coupons or whole FFRs contaminated with 5 log10 TCID50 (target concentration) SARS-CoV-2 in culture media, simulated saliva, or simulated lung fluid were dried for 1-2 h, then exposed to light from tanning and horticulture lamps to assess decontamination. Exposed coupons and whole FFRs showed SARS-CoV-2 inactivation for all matrices tested. Furthermore, FFRs still met performance specifications after five decontamination cycles. CONCLUSIONS: It is feasible that artificial sunlight from these sun lamps can be used to decontaminate FFRs provided the UV dose is sufficient and the light is unobstructed. Furthermore, decontamination can be performed up to five times without degrading FFR performance. SIGNIFICANCE AND IMPACT OF THE STUDY: This research shows a proof of principle that artificial sun lamps may be an option to decontaminate SARS-CoV-2 on N95 FFRs. UV doses required for inactivation to levels below detection ranged from 4 to 37·8 J cm-2 depending on the light source, virus matrix and FFR type.

The cluster model of ultraviolet disinfection explains tailing kinetics.

AIMS: To develop a new mathematical model derived from first principles to define the kinetics of ultraviolet disinfection and to explain the phenomenon known as tailing. The theory presented interprets tailing as the result of photoprotection due to cumulative Mie scattering effects in clustered populations of micro-organisms. METHODS AND RESULTS: Mie scattering effects at ultraviolet wavelengths are used to compute a shielding constant for each micro-organism based on the average projected diameter. An intrinsic rate constant, hypothesized to be a characteristic property of the microbial genome alone, is computed. The cluster model is fitted to tailing data from 30 ultraviolet inactivation studies and results are compared with the classic two stage multihit model. CONCLUSIONS: The cluster model demonstrates a statistically significant improvement in the mean adjusted R2 values of the tested data sets (P < 0·0001). Tailing in survival curves is the direct consequence of the Gaussian distribution of cluster sizes and the intrinsic rate constant is a real and critical parameter that defines ultraviolet susceptibility. SIGNIFICANCE AND IMPACT OF THE STUDY: The ultraviolet dose-response behaviour of micro-organisms can now be explained in terms of parameters that have physical meaning and provide deep insight into the disinfection process.

Modelling of ultraviolet light inactivation kinetics of methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus, Clostridium difficile spores and murine norovirus on fomite surfaces.

AIMS: Quantitative data on the doses needed to inactivate micro-organisms on fomites are not available for ultraviolet applications. The goal of this study was to determine the doses of UV light needed to reduce bacteria and murine norovirus (MNV) on hard surface fomites through experimentation and to identify appropriate models for predicting targeted levels of reduction. METHODS AND RESULTS: Stainless steel and Formica laminate coupons were selected as they are common surfaces found in healthcare settings. Test organisms included methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), Clostridium difficile and MNV. The fomites were inoculated with 105 -107 bacteria or virus and exposed to a range of UV doses. The order of resistance to UV irradiation was virus, bacterial spore and vegetative cell. The best fitting inactivation curves suggested nonlinear responses to increasing doses after a 3-4 log reduction in the test organisms. The average UV doses required for a 3 log reduction in the C. difficile, MRSA and VRE were 16 000, 6164 and 11 228 (mJ-s cm-2 ) for stainless steel, respectively, and 16 000, 11 727 and 12 441 (mJ-s cm-2 ) for Formica laminate, respectively. CONCLUSIONS: Higher UV light doses are required to inactivate bacteria and viruses on hard surfaces than in suspension. Greater doses are needed to inactivate bacterial spores and MNV compared to vegetative bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: Quantitative data and models on UV light doses needed to inactivate bacteria and MNV on hard surfaces are now available. The generalizable results of this study can be used to estimate required UV dosages to achieve targeted levels of inactivation based on estimated levels of contamination or to support quantitative microbial risk assessments.

Human enteric viruses in a wastewater treatment plant: evaluation of activated sludge combined with UV disinfection process reveals different removal performances for viruses with different features.

This study assess the quality of wastewater through the detection and quantification of important viruses causing gastroenteritis at different stages of the wastewater treatment process in an activated-sludge wastewater treatment plant with ultraviolet disinfection. Ten sampling events were carried out in a campaign along a period of 18 months collecting wastewater samples from the influent, after the activated-sludge treatment, and after the final disinfection with UV radiation. Samples were concentrated through ultracentrifugation and analysed using retro-transcription, PCR and real time quantitative PCR protocols, for detection and quantification of Group A Rotavirus (RVA), Human Astrovirus (HAstV), Norovirus Genogroup II (NoV GII) and Human Adenovirus (HAdV). HAdV (100%), NoV GII (90%), RVA (70%) and HAstV (60%) were detected in influent samples with concentration from 1·4 (NoV GII) to 8·0 (RVA) log10  gc l-1 . Activated-sludge treatment reached well quality effluents with low organic material concentration, although nonstatistical significant differences were registered among influent and postactivated sludge treatment samples, regarding the presence and concentration for most viruses. All post-UV samples were negative for NoV GII and HAstV, although RVA and HAdV were detected in 38% and 63% of those samples respectively, with concentration ranging from 2·2 to 5·5 and 3·1 to 3·4 log10  gc l-1 . SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrates that an activated-sludge wastewater treatment plant with UV disinfection reduces to levels below the detection limit those single-stranded RNA viruses as noroviruses and astroviruses and reach significant lower levels of rotaviruses and adenoviruses after the complete treatment process.