SARS-CoV-2 indoor environment contamination with epidemiological and experimental investigations

Research progress on environmental stability of SARS-CoV-2 and influenza viruses

We reviewed research on SARS-CoV-2 and influenza virus detection on surfaces, their persistence under various conditions, and response to disinfectants. Viral contamination in community and healthcare settings was analyzed, emphasizing survival on surfaces influenced by temperature, pH, and material. Findings showed higher concentrations enhance survivability at room temperature, whereas stability increases at 4°C. Both viruses decline in low pH and high heat, with influenza affected by salinity. On various material surfaces, SARS-CoV-2 and influenza viruses demonstrate considerable variations in survival durations, and SARS-CoV-2 is more stable than influenza virus. On the skin, both virus types can persist for ≥2 h. Next, we delineated the virucidal efficacy of disinfectants against SARS-CoV-2 and influenza viruses. In daily life, exposure to ethanol (70%), isopropanol (70%), bleach (10%), or hydrogen peroxide (1-3%) for 15-30 min can effectively inactive various SARS-CoV-2 variants. Povidone-iodine (1 mg/mL, 1 min) or cetylpyridinium chloride (0.1 mg/mL, 2 min) may be used to inactive different SARS-CoV-2 variants in the mouth. Chlorine disinfectants (500 mg/L) or ultraviolet light (222 nm) can effectively inhibit different SARS-CoV-2 variants in public spaces. In conclusion, our study provides a scientific basis and practical guidance for reduction of viral persistence (retention of infectivity) on surfaces and environmental cleanliness.

A Pilot Study of Aerosolization of Infectious Murine Norovirus in an Experimental Setup

Human norovirus is transmitted mainly via the faecal-oral route, but norovirus disease outbreaks have been reported in which airborne transmission has been suggested as the only explanation. We used murine norovirus (MNV) as a surrogate for human norovirus to determine the aerosolization of infectious norovirus in an experimental setup. A 3-l air chamber system was used for aerosolization of MNV. Virus in solution (6 log10 TCID50/ml) was introduced into the nebulizer for generating aerosols and a RAW 264.7 cell dish without a lid was placed in the air chamber. Cell culture medium samples were taken from the dishes after the aerosol exposure time of 30 or 90 min, and the dishes were placed in a 37 °C, 5% CO2 incubator and inspected with a light microscope for viral cytopathic effects (CPEs). We determined both the infectious MNV TCID50 titre and used an RT-qPCR assay. During the experiments, virus infectivity remained stable for 30 and 90 min in the MNV solution in the nebulizer. Infectious MNV TCID50 values/ml of 2.89 ± 0.29 and 3.20 ± 0.49 log10 were measured in the chamber in RAW 264.7 cell dish media after the 30-min and 90-min exposure, respectively. The MNV RNA loads were 6.20 ± 0.24 and 6.93 ± 1.02 log10 genome copies/ml, respectively. Later, a typical MNV CPE appeared in the aerosol-exposed RAW cell dishes. We demonstrated that MNV was aerosolized and that it remained infectious in the experimental setup used. Further studies required for understanding the behaviour of MNV in aerosols can thus be performed.

Monitoring Prevalence and Persistence of Environmental Contamination by SARS-CoV-2 RNA in a Makeshift Hospital for Asymptomatic and Very Mild COVID-19 Patients

Objective: To investigate the details of environmental contamination status by SARS-CoV-2 in a makeshift COVID-19 hospital. Methods: Environmental samples were collected from a makeshift hospital. The extent of contamination was assessed by quantitative reverse transcription polymerase chain reaction (RT-qPCR) for SARS-CoV-2 RNA from various samples. Results: There was a wide range of total collected samples contaminated with SARS-CoV-2 RNA, ranging from 8.47% to 100%. Results revealed that 70.00% of sewage from the bathroom and 48.19% of air samples were positive. The highest rate of contamination was found from the no-touch surfaces (73.07%) and the lowest from frequently touched surfaces (33.40%). The most contaminated objects were the top surfaces of patient cubic partitions (100%). The median Ct values among strongly positive samples were 33.38 (IQR, 31.69-35.07) and 33.24 (IQR, 31.33-34.34) for ORF1ab and N genes, respectively. SARS-CoV-2 relic RNA can be detected on indoor surfaces for up to 20 days. Conclusion: The findings show a higher prevalence and persistence in detecting the presence of SARS-CoV-2 in the makeshift COVID-19 hospital setting. The contamination mode of droplet deposition may be more common than contaminated touches.

Detection of hospital environmental contamination during SARS-CoV-2 Omicron predominance using a highly sensitive air sampling device

Background and objectives

The high transmissibility of SARS-CoV-2 has exposed weaknesses in our infection control and detection measures, particularly in healthcare settings. Aerial sampling has evolved from passive impact filters to active sampling using negative pressure to expose culture substrate for virus detection. We evaluated the effectiveness of an active air sampling device as a potential surveillance system in detecting hospital pathogens, for augmenting containment measures to prevent nosocomial transmission, using SARS-CoV-2 as a surrogate.

Methods

We conducted air sampling in a hospital environment using the AerosolSense^TM air sampling device and compared it with surface swabs for their capacity to detect SARS-CoV-2.

Results

When combined with RT-qPCR detection, we found the device provided consistent SARS-CoV-2 detection, compared to surface sampling, in as little as 2 h of sampling time. The device also showed that it can identify minute quantities of SARS-CoV-2 in designated "clean areas" and through a N95 mask, indicating good surveillance capacity and sensitivity of the device in hospital settings.

Conclusion

Active air sampling was shown to be a sensitive surveillance system in healthcare settings. Findings from this study can also be applied in an organism agnostic manner for surveillance in the hospital, improving our ability to contain and prevent nosocomial outbreaks.

Combining Phi6 as a surrogate virus and computational large-eddy simulations to study airborne transmission of SARS-CoV-2 in a restaurant

COVID-19 has highlighted the need for indoor risk-reduction strategies. Our aim is to provide information about the virus dispersion and attempts to reduce the infection risk. Indoor transmission was studied simulating a dining situation in a restaurant. Aerosolized Phi6 viruses were detected with several methods. The aerosol dispersion was modeled by using the Large-Eddy Simulation (LES) technique. Three risk-reduction strategies were studied: (1) augmenting ventilation with air purifiers, (2) spatial partitioning with dividers, and (3) combination of 1 and 2. In all simulations infectious viruses were detected throughout the space proving the existence long-distance aerosol transmission indoors. Experimental cumulative virus numbers and LES dispersion results were qualitatively similar. The LES results were further utilized to derive the evolution of infection probability. Air purifiers augmenting the effective ventilation rate by 65% reduced the spatially averaged infection probability by 30%-32%. This relative reduction manifests with approximately 15 min lag as aerosol dispersion only gradually reaches the purifier units. Both viral findings and LES results confirm that spatial partitioning has a negligible effect on the mean infection-probability indoors, but may affect the local levels adversely. Exploitation of high-resolution LES jointly with microbiological measurements enables an informative interpretation of the experimental results and facilitates a more complete risk assessment.