Résumé
Escherichia coli O157:H7 is a major cause of foodborne disease outbreaks throughout the world, while methicillin-resistant Staphylococcus aureus (MRSA) is responsible for many difficult-to-treat infections in humans. Ultraviolet (UV) irradiation is commonly used for disinfection in food processing, medical facilities, and water treatment to prevent the transmission of these pathogen. With increased use of UV disinfection technologies over the last few years because of COVID-19 and concerns about other communicable disease, it has become a concern that microbial species could develop tolerance to UV irradiation, especially when it is applied continuously. To elucidate the effect of continuous UV exposure at different wavelengths and power levels on the tolerance development of bacteria, Escherichia coli O157:H7 and MRSA)USA300 growths were investigated by continuously exposing inoculated agar plates to six different commercially available UV sources at wavelengths of 222 nm, 254 nm, 275 nm, and 405 nm. The agar plates in these experiments were partially covered by a thin acrylic sheet, which provided either complete protection from the UV to the cells directly under the sheet, no protection if significantly away from the sheet, or partial protection near the edges of the sheet due to shading or small amounts of UV reflection under the sheet at the edges. In these experiments, tolerant cells of E. coli and S. aureus were found from the 222 nm, the 405 nm, and one of the 254 nm sources. Upon examination of the power of each UV source, it was shown that the 275 nm and 254 nm sources that resulted in no tolerant cells had surface power densities [at 25 cm (10 in.)] that were more than 10-200 times greater than those that had tolerant cells. These results suggests that bacterial cells have a higher chance to develop UV tolerance under lower power UV sources (under the experimental conditions in our laboratory). Genome investigation of the tolerant colonies revealed that there are no significant differences between the cells that developed tolerance and the original organism, hinting at the need to explore the role of epigenetics mechanisms in the development of UV tolerance in these bacteria. © 2023 American Society of Civil Engineers.
Résumé
Background. The COVID-19 pandemic is an ongoing global health emergency. Wastewater-based epidemiology is a valuable tool for supplementing clinical testing in identifying infected individuals early thus containing disease transmission. To assess early detection of COVID-19, a building-level wastewater-based surveillance pilot project was implemented within VHA. Here, we report the results from 2 methods of polymerase chain reaction (PCR) testing of 1073 wastewater samples from VHA CLCs (i.e., nursing homes). Methods. Daily (Monday-Friday) wastewater samples were collected (January 11, 2021, to July 2, 2021) at eight CLCs located across the US and shipped overnight for processing. The samples were heat inactivated by incubating samples in a 65+/-1degreeC heating circulating water bath for 90 minutes. The virus in the wastewater was concentrated using InnovaPrep concentrating pipette select, and RNA was isolated from the concentrate and subjected to reverse transcription quantitative PCR (RT-qPCR) and RT-digital PCR. If SARS-CoV-2 was detected in the wastewater within the prior 10 days of a virus-positive occupant, the wastewater positivity was regarded as an early warning. Results. Twenty-seven positives and 7 inconclusive results were reported by RT-qPCR during the surveillance. Among the 27, 15 wastewater positives qualified as early warning and 12 positives were not verified by occupant positivity. Digital PCR with a cutoff value of 0.25 copies/uL of RNA for defining positivity had 28 positives qualifying as early warnings, and 115 positives were not verified by occupant positivity (Figure 1). Conclusion. The overall viral loads of the wastewater samples were very low corresponding to the dip in cases seen in the US during the pilot period. Although sensitivity of digital PCR appears (based on 0.25 copies/uL of RNA for defining positivity) higher than that of RT-qPCR, there were more occurrences of unverified early warning that could impact precision. The cut-off selected for RT-digital PCR reported here is arbitrary and lacks industry consensus. More controlled studies are needed to determine sensitivity and precision as well as to standardize RT-digital PCR cutoffs to define positivity for routine use.