Virucidal Efficiency Research Articles

Nanomolar concentrations of the photodynamic compound TLD-1433 effectively inactivate numerous human pathogenic viruses

The anti-viral properties of a small (≈1 kDa), novel Ru(II) photo dynamic compound (PDC), referred to as TLD-1433 (Ruvidar™), are presented. TLD-1433 had previously been demonstrated to exert strong anti-bacterial and anti-cancer properties. We evaluated the capacity of TLD-1433 to inactivate several human pathogenic viruses. TLD-1433 that was not photo-activated was capable of effectively inactivating 50 % of influenza H1N1 virus (ID50) at a concentration of 117 nM. After photo-activation, the ID50 was reduced to <10 nM. The dose of photo-activated TLD-1433 needed to reduce H1N1 infectivity >99 % (ID99) was approximately 170 nM. Similarly, the ID99 of photo-activated TLD-1433 was determined to range from about 20 to 120 nM for other tested enveloped viruses; specifically, a human coronavirus, herpes simplex virus, the poxvirus Vaccinia virus, and Zika virus. TLD-1433 also inactivated two tested non-enveloped viruses; specifically, adenovirus type 5 and mammalian orthoreovirus, but at considerably higher concentrations. Analyses of TLD-1433-treated membranes suggested that lipid peroxidation was a major contributor to enveloped virus inactivation. TLD-1433-mediated virus inactivation was temperature-dependent, with approximately 10-fold more efficient virucidal activity when viruses were treated at 37 °C than when treated at room temperature (∼22 °C). The presence of fetal bovine serum and virus solution turbidity reduced TLD-1433-mediated virucidal efficiency. Immunoblots of TLD-1433-treated human coronavirus indicated the treated spike protein remained particle-associated.

Inactivation of influenza virus as representative of enveloped RNA viruses on photocatalytically active nanoparticle and nanotubular TiO2 surfaces

The recent pandemic showed us that there is a strong demand for standardized methods to evaluate the antiviral activity of different materials using enveloped RNA viruses (e.g. SARS-CoV-2, influenza virus). Virucidal activity can be achieved as a result of photoexcitation of a TiO2 photocatalyst under UV illumination. All standardized methods evaluating the virucidal activity of photocatalytic surfaces use bacteriophage Q-beta, a representative of small non-enveloped viruses. This work was thus devoted to the evaluation of the virucidal efficiency of photocatalytically active nanostructured TiO2 surfaces (nanotubular and nanoparticle) to inactivate the influenza virus with particular interest paid to the methodology of virucidal testing and the influence of the surface nanostructure (porosity). Two different TiO2 nanostructures were used in this study, namely nanoparticle and nanotubular structures. A significant decrease in the amount of viral RNA and titre was obtained after rinsing, because the virus was retained on the surface of the nanostructured TiO2 during exposure in the dark. The decrease can be understood as an additional effect of the surface porosity on the TiO2 virucidal activity after UV illumination. However, this fact was taken into account in the calculation of virucidal activity due to UV light. Both nanostructured TiO2 coatings have comparable porosity and thickness, but the photocatalytic activity (to oxidatively degrade aqueous pollutants) is higher for the nanoparticle than for the nanotubular surface. On the other hand, the virucidal activity is much higher for the nanotubular surface. This can be explained by the uniform and open structure of nanotubes resulting in a lower amount of virus being retained on the surface under dark conditions and the high surface area of the nanotubes.

Virucidal PVP-Copper Salt Composites against Coronavirus Produced by Electrospinning and Electrospraying.

Electrospinning technology was used to produced polyvinylpyrrolidone (PVP)-copper salt composites with structural differences, and their virucidal activity against coronavirus was investigated. The solutions were prepared with 20, 13.3, 10, and 6.6% w/v PVP containing 3, 1.0, 0.6, and 0.2% w/v Cu (II), respectively. The rheological properties and electrical conductivity contributing to the formation of the morphologies of the composite materials were observed by scanning electron microscopy (SEM). SEM images revealed the formation of electrospun PVP-copper salt ultrafine composite fibers (0.80 ± 0.35 µm) and electrosprayed PVP-copper salt composite microparticles (1.50 ± 0.70 µm). Energy-dispersive X-ray spectroscopy (EDS) evidenced the incorporation of copper into the produced composite materials. IR spectra confirmed the chemical composition and showed an interaction of Cu (II) ions with oxygen in the PVP resonant ring. Virucidal composite fibers inactivated 99.999% of coronavirus within 5 min of contact time, with moderate cytotoxicity to L929 cells, whereas the virucidal composite microparticles presented with a virucidal efficiency of 99.999% within 1440 min of exposure, with low cytotoxicity to L929 cells (mouse fibroblast). This produced virucidal composite materials have the potential to be applied in respirators, personal protective equipment, self-cleaning surfaces, and to fabric coat personal protective equipment against SARS-CoV-2, viral outbreaks, or pandemics.

Biocompatible curcumin coupled nanofibrous membrane for pathogens sterilization and isolation

Airborne transmission of pathogens is the most probable cause for the spread of respiratory diseases, which can be intercepted by personal protective equipment such as masks. In this study, an efficient antiviral personal protective filter was fabricated by coupling the biocompatible curcumin (CCM) with nanofibrous polytetrafluoroethylene (PTFE) membrane. The CCM extracted from plants was first dissolved in acidified ethanol at a certain pH and temperature to optimize its loading concentration, antiviral activation, and binding forces on the polyethylene terephthalate (PET) support to form a pre-filtration layer at the front section of the filter. Ultrathin PTFE membrane was then fabricated on the antibacterial-antiviral PET support (A-A PET) by controllable heating lamination. This functional layer of the filter exhibits good gas permeance (3423.6 m3/(m2·h·kPa)) and ultrafine particles rejection rate (>98.79%). Moreover, the obtained A-A filter exhibit a high antibacterial rate against a variety of bacteria (E. coli, B. subtilis, A. niger, and Penicillium were 99.84%, 99.02%, 93.60%, 95.23%, respectively). Forthwith virucidal (SARS-CoV-2) efficiency of the A-A filter can reach 99.90% for 5 min. The filter shows good stability after 10 heating cycles, demonstrating its reusability.

Dental Care and Education Facing Highly Transmissible SARS-CoV-2 Variants: Prospective Biosafety Setting: Prospective, Single-Arm, Single-Center Study.

With the arrival of the highly transmissible Omicron variants (BA.4 and BA.5), dentistry faces another seasonal challenge to preserve the biosafety of dental care and education. With the aim of protecting patients, students, teachers and healthcare professionals, this paper introduces a prospective sustainable biosafety setting for everyday dental care and education. The setting developed by dental clinicians, epidemiologists, and teachers of dentistry consists of a combination of modern technologies focused on the air-borne part of the viral pathway. The introduced biosafety setting has been clinically evaluated after 18 months of application in the real clinical environment. The protocol has three fundamental pillars: (1) UVC air disinfection; (2) air saturation with certified virucidal essences with nebulizing diffusers; (3) complementary solutions including telehealth and 3D printing. A pseudonymous online smart form was used as the evaluation method. The protocol operates on the premise that everybody is a hypothetical asymptomatic carrier. The results of a clinical evaluation of 115 patient feedbacks imply that no virus transmission from patient to patient or from doctor to nurse was observed or reported using this protocol, and vice versa, although nine patients retrospectively admitted that the clinic visit is likely to be infectious. Despite these promising results, a larger clinical sample and exposition to the current mutated strains are needed for reliable conclusions about protocol virucidal efficiency in current dental environments.

UV-LED irradiation reduces the infectivity of herpes simplex virus type 1 by targeting different viral components depending on the peak wavelength.

Herpes simplex virus type 1 (HSV-1) is an enveloped virus that mainly infects humans. Given its high global prevalence, disinfection is critical for reducing the risk of infection. Ultraviolet-light-emitting diodes (UV-LEDs) are eco-friendly irradiating modules with different peak wavelengths, but the molecules degraded by UV-LED irradiation have not been clarified. To identify the target viral molecules of UV-LEDs, we exposed HSV-1 suspensions to UV-LED irradiation at wavelengths of 260-, 280-, 310-, and 365-nm and measured viral DNA, protein, and lipid damage and infectivity in host cells. All UV-LEDs substantially reduced by inhibiting host cell transcription, but 260- and 280-nm UV-LEDs had significantly stronger virucidal efficiency than 310- and 365-nm UV-LEDs. Meanwhile, 260- and 280-nm UV-LEDs induced the formation of viral DNA photoproducts and the degradation of viral proteins and some phosphoglycerolipid species. Unlike 260- and 280-nm UV-LEDs, 310- and 365-nm UV-LEDs decreased the viral protein levels, but they did not drastically change the levels of viral DNA photoproducts and lipophilic metabolites. These results suggest that UV-LEDs reduce the infectivity of HSV-1 by targeting different viral molecules based on the peak wavelength. These findings could facilitate the optimization of UV-LED irradiation for viral inactivation.

Novel Cationic Meso-Arylporphyrins and Their Antiviral Activity against HSV-1.

This work is devoted to the search for new antiherpes simplex virus type 1 (HSV-1) drugs among synthetic tetrapyrroles and to an investigation of their antiviral properties under nonphotodynamic conditions. In this study, novel amphiphilic 5,10,15,20-tetrakis(4-(3-pyridyl-n-propanoyl)oxyphenyl)porphyrin tetrabromide (3a), 5,10,15,20-tetrakis(4-(6-pyridyl-n-hexanoyl)oxyphenyl)porphyrin tetrabromide (3b) and known 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetraiodide (TMePyP) were synthesized, and their dark antiviral activity in vitro against HSV-1 was studied. The influence of porphyrin’s nanosized delivery vehicles based on Pluronic F127 on anti-HSV-1 activity was estimated. All the received compounds 3a, 3b and TMePyP showed virucidal efficiency and had an effect on viral replication stages. The new compound 3b showed the highest antiviral activity, close to 100%, with the lowest concentration, while the maximum TMePyP activity was observed with a high concentration; porphyrin 3a was the least active. The inclusion of the synthesized compounds in Pluronic F-127 polymeric micelles had a noticeable effect on antiviral activity only at higher porphyrin concentrations. Action of the received compounds differs by influence on the early or later reproduction stages. While 3a and TMePyP acted on all stages of the viral replication cycle, porphyrin 3b inhibited viral replication during the early stages of infection. The resulting compounds are promising for the development of utilitarian antiviral agents and, possibly, medical antiviral drugs.

Antibacterial and antiviral N-halamine nanofibrous membranes with nanonet structure for bioprotective applications

The recent outbreak of a coronavirus disease (COVID-19) has posed a great threat to public health and financial system. Most current masks used to prevent the spread of COVID-19 are typically absence of biocidal properties. We designed a novel polymer, polystyrene grafted by 5, 5-dimethylhydantoin and trimethylamine (PSDT), which possesses halamine site and cationic quaternary ammonia salt site. Furthermore, PSDT/PU nanofiber@net membranes (PSDT/PU NNMs) were obtained by electrospinning technology. Our strategy enables inherent N-halamine and quaternary ammonia salt (QAS) group to be covalently integrated into membranes, realizing the efficient and stable biocidal properties. Meanwhile, the introduction of nanonets endows electrospun membranes with prominent air filtration performance. The resulting membranes exhibit integrated properties of high interception of fine particles (96.7%) and low pressure drop (95.4 Pa). Besides, chlorinated PSDT/PU nanofiber@net membranes (with active chlorine content of 0.60 wt% and quaternary ammonia salt content of 2.20 wt%) exhibited superior bactericidal (>99.9999%) and virucidal (>99.999%) efficiency in a short time (2 min), which enables chlorinated PSDT/PU NNMs to be served as the filtration material by providing bacterial interception (99.77%) and contact killing against pathogens. The successful synthesis of PSDT/PU NNMs provide innovative insights for exploring filtration materials in a nanonet and biocidal form.

Synergistic effects of anionic surfactants on coronavirus (SARS-CoV-2) virucidal efficiency of sanitizing fluids to fight COVID-19

Our surrounding environment, especially often-touched contaminated surfaces, plays an important role in the transmission of pathogens in society. The shortage of effective sanitizing fluids, however, became a global challenge quickly after the coronavirus disease-19 (COVID-19) outbreak in December 2019. In this study, we present the effect of surfactants on coronavirus (SARS-CoV-2) virucidal efficiency in sanitizing fluids. Sodium dodecylbenzenesulfonate (SDBS), sodium laureth sulfate (SLS), and two commercial dish soap and liquid hand soap were studied with the goal of evaporation rate reduction in sanitizing liquids to maximize surface contact time. Twelve fluids with different recipes composed of ethanol, isopropanol, SDBS, SLS, glycerin, and water of standardized hardness (WSH) were tested for their evaporation time and virucidal efficiency. Evaporation time increased by 17–63% when surfactant agents were added to the liquid. In addition, surfactant incorporation enhanced the virucidal efficiency between 15 and 27% according to the 4-field test in the EN 16615:2015 European Standard method. Most importantly, however, we found that surfactant addition provides a synergistic effect with alcohols to inactivate the SARS-CoV-2 virus. This study provides a simple, yet effective solution to improve the virucidal efficiency of commonly used sanitizers.

A comparative analysis of virucidal efficiency of biocide agents

The main groups of biocide agents used for inactivation of bacteria and viruses were studied for their virucidal activity against enveloped (HIV, viral hepatitis C, influenza virus A) and non-enveloped viruses (poliovirus, adenovirus). Their efficiency was analyzed. Quarterly ammonium compounds (QAC) themselves are not able to properly inactivate non-enveloped viruses. However, they can be successfully applied in combination with other biocides (guanidines, aldehydes). Effective composition of QAC with amines and guanidines provided inactivation of viruses (4.0 lgTCID50) in concentrations of 0.166-0.280% for non-enveloped viruses and 0.080-00.185% for enveloped viruses. The combination of QAC with aldehydes is especially effective (0.04-0.64% for non-enveloped viruses). The virucidal efficiency does not directly depend on the QAC concentration in the chemical disinfectants.

Virucidal Efficiency of Chemical Agents: A comparative Analysis

Present study was designed to explore the influences of different categories of chemical factors, such as organic solvents, oxidizing agents, anionic detergent and dye on persistence of locally isolated coliphages and shigaphages from clinical sewage samples. Thirty percent ethanol initiated 83.20 and 62.86% reduction in the number of coliphage and shigaphage plaques in our study respectively. Chloroform mediated decrease in our observation was 53.13 and 88.33% for coliphages and shigaphages, respectively. The number of the shigaphage plaques was reduced by 62.5% following biphasic diethyl ether (DEE) treatment. About 72.66% of coliphages were deactivated after exposure to biphasic diethyl ether. Exposure of the isolated coliphages and shigaphages to 1% formalin had completely destroyed the viability of the bacteriophages. Coliphage survival in this investigation was 37.5% and 2.4% following treatment with 0.3 and 3.0% hydrogen peroxide respectively. The decrease in overall coliphage and shigaphage population was 95.83% and 94.14% while treated with 0.5% sodium dodecyl sulfate (SDS). The number increased for the viruses infecting E. coli by 9.52% where the number of shigaphages declined by 14.63% while growing in presence of a divalent cation [Ca(NO3)2]. Coliphage and shigaphage populations were diminished by 61. 76% and 53.48% respectively after treatment with the neutral red (0.0075%) followed by exposure to visible light.Bangladesh J Microbiol, Volume 31, Number 1-2,June-Dec 2014, pp 47-52

Inactivation of virus in solution by cold atmospheric pressure plasma: identification of chemical inactivation pathways

Cold atmospheric pressure plasma (CAP) inactivates bacteria and virus through in situ production of reactive oxygen and nitrogen species (RONS). While the bactericidal and virucidal efficiency of plasmas is well established, there is limited knowledge about the chemistry leading to the pathogen inactivation. This article describes a chemical analysis of the CAP reactive chemistry involved in the inactivation of feline calicivirus. We used a remote radio frequency CAP produced in varying gas mixtures leading to different plasma-induced chemistries. A study of the effects of selected scavengers complemented with positive control measurements of relevant RONS reveal two distinctive pathways based on singlet oxygen and peroxynitrous acid. The first mechanism is favored in the presence of oxygen and the second in the presence of air when a significant pH reduction is induced in the solution by the plasma. Additionally, smaller effects of the H2O2, O3 and produced were also found. Identification of singlet oxygen-mediated 2-imidazolone/2-oxo-His (His +14 Da)—an oxidative modification of His 262 comprising the capsid protein of feline calicivirus links the plasma induced singlet oxygen chemistry to viral inactivation.

Adenovirus inactivation by in situ photocatalytically and photoelectrocatalytically generated halogen viricides.

This study investigates and compares the virucidal performances of photocatalytic (PC) and photoelectrocatalytic (PEC) treatments in the presence and absence of halides, such as Br- and Cl-, under comparable experimental conditions. The results confirm that the PC virucidal efficiency can be enhanced in the presence of low halide concentrations (e.g., X=Br- or Cl-) and further enhanced by applying potential bias onto the photoanode in a PEC system. The PEC treatment in the presence of 1.0mM Br (PEC-Br) shows the highest virucidal efficiency, enabling complete inactivation of a ∼1000 TCID50 replication-deficient recombinant adenovirus (RDRADS) population within 31.7s. The superior virucidal performances of PEC-X treatments can be attributed to the increased production of active oxygen species and additional viricides resulting from the PEC halide oxidation, as well as prolonged lifetime of photoholes (h+ ) for direct inactivation. The findings of this work confirm that new forms of active species generated in situ via a PC or PEC process are effective for viruses.

Comparison of the virucidal efficiency of peracetic acid, potassium monopersulfate and sodium hypochlorite on hepatitis A and enteric cytopathogenic bovine orphan virus

The virucidal activity of peroxy-products was evaluated and compared with sodium hypochlorite using the EN 14675 European suspension test and a surface test developed in our laboratory. The classical approach on infectivity of viruses was complemented with a prospective approach on virus genomes. Both infectivity tests were adapted and/or developed to determine the activity of disinfectants against reference bovine enterovirus type 1 [enteric cytopathogenic bovine orphan virus (ECBO)] and resistant hepatitis A virus (HAV) in conditions simulating practical use. Similar concentrations of active chlorine were virucidal against both viruses, either at 0·062% using the suspension test or at 0·50-1% using the surface test. However, for potassium monopersulfate and peracetic acid products, concentrations of approximately three times (3%) to 72 times (9%) higher were necessary against HAV than ECBO when determined with the suspension test. With the surface test, 4-8% peroxy-products were virucidal against HAV, either 16 times more peroxy-products concentrations than against ECBO. No significant impact on the targeted area of the viral genome measured by real-time RT-PCRs was obtained for ECBO and HAV suspensions treated with disinfectants, even with doses higher than the minimal virucidal concentrations. Sodium hypochlorite, but not peroxy-products, had similar activity against ECBO and HAV. No relation could be established between infectivity tests and genome destruction. This is the first comparative study that investigates with novel suspension and surface tests the reduction of infectivity and genome destruction of two resistant viruses by peroxy-compounds. The results and conclusions collected with European standards are discussed.

Chlorine Dioxide Inactivation of Enterovirus 71 in Water and Its Impact on Genomic Targets

To control the waterborne transmission of enterovirus 71(EV71), which is associated with hand foot and mouth disease (HFMD), it is essential to know the inactivation effectiveness of disinfectants on EV71 in water. In this article, we present a comparative analysis of the effects on EV71 following exposure to chlorine dioxide (ClO2) under different doses, pH, and temperature conditions. We show that the EV71 exhibited strong resistance to ClO2 (more than the MS2 standard) and that Ct value ranges required for a 4-log reduction of EV71 in buffered, disinfectant demand-free water at pH 7.2 and 20 °C by ClO2 were 4.24-6.62 mg/L·min according to the efficiency factor Hom model. ClO2 inactivation of the virus was temperature- and pH-dependent. The virucidal efficiency was higher at pH 8.2 than at pH 5.6 and pH 7.2 and higher at 36 °C than at 4 and 20 °C. In addition, we also observed the impact of ClO2 on the entire viral genome using RT-PCR, which indicated that the 5' noncoding region (5'-NCR) within the EV71 genome, specifically the 1-118 nt region, was the most easily damaged by ClO2 and correlated with viral infectivity. Our study has not only provided guidelines for EV71 disinfection strategies of waste and drinking water, but also confirmed the importance of the 5'-NCR for EV71 infectivity and may demonstrate a general inactivation by ClO2 of enteric virus by damaging the 5'-NCR. Furthermore, 5'-NCR can be used as a target region for PCR to investigate infectious virus contamination in environmental water and evaluate the inactivation effects of ClO2.

Evaluation of the virucidal performance of domestic laundry procedures

Laundering is one of the most important means to ensure a sufficient hygiene standard in the household environment. To evaluate the performance of this process, it is desirable to have methods that mimic the real-life situation as closely as possible. Although methods for the evaluation of the antibacterial and antifungal efficacy of domestic laundry procedures are available, the effect of laundering on viruses is still rather unclear. As the influence of laundry process parameters such as mechanical actions, temperature dynamics or liquor ratio cannot be simulated in vitro by suspension assays, a new in situ test method allowing virus simulation tests in washing machines has been developed. Using this in situ method we could show that conventional household washing detergents have a full virucidal efficiency at 40 degrees C also against non-enveloped surrogate viruses.

Inactivation of particle-associated viruses by UV

Ultraviolet (UV) disinfection of bacteriophage MS2 in different waters containing particles was studied and a two-stage survival phenomenon was observed. It was found that turbidity had a negative impact on UV disinfection. In addition, the presence of fecal coliforms ( E. coli C) was discovered to have an adverse effect on the virucidal efficiency of UV disinfection. It was also noted that the efficiency of UV disinfection was affected by particle size, number of particles, and particle size distribution. It was assumed that the indicator organisms in the water could be classified into two main categories, namely protected and less-protected to UV irradiation. In the less-protected group, viruses were assumed to exist in a dispersed state. In the protected group, on the other hand, viruses were assumed to exist in a particle-associated state. Based on this assumption, a model was derived for describing the measured inactivation of particle-associated viruses exposed to UV light. The results predicted by the proposed model were in good agreement with the experimental data.

Virucidal activity and cytotoxicity of the liposomal formulation of povidone-iodine

Two drug formulations of povidone-iodine (PVP-I)—an aqueous PVP-I solution (Betaisodona®) and a liposomal PVP-I formulation—were tested for their virucidal activity and cytotoxicity in cell culture. As to the virudical activity against influenza A virus, herpes simplex virus type 1, adenovirus type 8 and human rhinovirus type 14, the liposomal formulation of PVP-I proved to be approximately as active as the aqueous one. Half maximum cytotoxic PVP-I concentrations were 0.01–0.07% for aqueous PVP-I and 0.03–0.27% for the liposomal PVP-I formulation (XTT reduction assay EZ4U). The detection of lactate dehydrogenase (LDH) release, DNA fragmentation (ELISA) and DNA strand breakage (TUNEL assay) after 24 h exposure of human embryonic lung fibroblasts to PVP-I revealed that necrosis predominates in cells treated with aqueous 0.08–0.32% PVP-I solutions, whereas apoptosis was the predominant type of cell death in cells treated with equivalent concentrations of liposomal PVP-I formulation. The favorable virucidal efficiency together with the preferred apoptotic route of cell death makes the liposomal PVP-I formulation a promising candidate for topical use in prevention and treatment of infections of the eye and the upper respiratory tract.

Virucidal activity of disinfectants: virucidal activities of disinfectants on some viruses coated on several materials and its durability

First, four disinfectants were tested for virucidal activity on viruses coated upon materials. Disinfectants of the aldehyde and halogen groups had a destructive effect on both enveloped and non-enveloped DNA and RNA viruses coated on a cotton gauze, stainless chips, wood shavings, polyplopylene resin chips and latex resin chips, respectively. Disinfectant of the biguanide group had a virucidal activity on both enveloped DNA and RNA viruses. Secondary, five disinfectants were tested for the durability of their virucidal activity on two DNA and RNA viruses after preparing working solutions. The disinfectants of the aldehyde group maintained their virucidal efficiency for 2 to 3 days. Disinfectants of the invert and amphoteric soap groups, the biguanide group and the halogen group maintained their virucidal efficiency for 1 to 2 days. In the presence of bovine serum, the virucidal activity of the aldehyde group and the halogen group were not influenced but that of the invert and amphoteric soap groups were strongly influenced and lost their effect.

Inactivation of human and simian rotaviruses by chlorine dioxide

The inactivation of single-particle stocks of human (type 2, Wa) and simian (SA-11) rotaviruses by chlorine dioxide was investigated. Experiments were conducted at 4 degrees C in a standard phosphate-carbonate buffer. Both virus types were rapidly inactivated, within 20 s under alkaline conditions, when chlorine dioxide concentrations ranging from 0.05 to 0.2 mg/liter were used. Similar reductions of 10(5)-fold in infectivity required additional exposure time of 120 s at 0.2 mg/liter for Wa and at 0.5 mg/liter for SA-11, respectively, at pH 6.0. The inactivation of both virus types was moderate at neutral pH, and the sensitivities to chlorine dioxide were similar. The observed enhancement of virucidal efficiency with increasing pH was contrary to earlier findings with chlorine- and ozone-treated rotavirus particles, where efficiencies decreased with increasing alkalinity. Comparison of 99.9% virus inactivation times revealed ozone to be the most effective virucidal agent among these three disinfectants.