Virtual Care in Canada as of the Sixth Wave of the COVID-19 Pandemic: Finding the Right Balance - An Indigenous Perspective.

The constraints of the COVID-19 pandemic accelerated the adoption of virtual care. The role of virtual care in the mix of healthcare services is being re-examined as the pandemic evolves. For many diverse Indigenous communities (rural, remote, urban), virtual care has the potential to increase access to healthcare and improv health outcomes, or to worsen existing inequities. Thoughtful co-design of virtual care programs, attention to user experience and enabling policy decisions can unlock the potential of virtual care for Indigenous individuals and communities.

New Perylene Diimide Ink for Interlayer Formation in Air-Processed Conventional Organic Photovoltaic Devices.

Roll-to-roll coating of conventional organic photovoltaic architectures in air necessitates low work function, electron-harvesting interlayers as the top interface, termed cathode interlayers. Traditional materials based on metal oxides are often not compatible with coating in air and/or green solvents, require thermal annealing, and are limited in feasibility due to interactions with underlying layers. Alternatively, perylene diimide materials offer easily tunable redox properties, are amenable to air coating in green solvents, and are considered champion organic-based cathode interlayers. However, underlying mechanisms of the extraction of photogenerated electrons are less well understood. Herein, we demonstrate the utilization of two N-annulated perylene diimide materials, namely, PDIN-H and CN-PDIN-H, in air-processed conventional organic photovoltaic devices, using the now standard PM6:Y6 photoactive layer. The processing ink formulation using cesium carbonate as a processing agent to solubilize the perylene diimides in suitable green solvents (1-propanol and ethyl acetate) for uniform film formation using spin or slot-die coating on top of the photoactive layer is critical. Cesium carbonate remains in the film, creating hybrid organic/metal salt cathode interlayers. Best organic photovoltaic devices have power conversion efficiencies of 13.2% with a spin-coated interlayer and 13.1% with a slot-die-coated interlayer, superior to control devices using the classic conjugated polyelectrolyte PFN-Br as an interlayer (ca. 12.8%). The cathode interlayers were found to be semi-insulating in nature, and the device performance improvements were attributed to beneficial interfacial effects and electron tunneling through sufficiently thin layers. The efficiencies beyond 13% achieved in air-processed organic photovoltaic devices utilizing slot-die-coated cathode interlayers are among the highest reported so far, opening new opportunities for the fabrication of large-area solar cell modules.

Zinc Oxide-Perylene Diimide Hybrid Electron Transport Layers for Air-Processed Inverted Organic Photovoltaic Devices.

In this work, we report the formation of perylene diimide films, from green solvents, for use as electron transporting layers, when combined with ZnO, in inverted-type organic photovoltaics. A modified N-annulated PDI was functionalized with a tert-butyloxycarbonyl protecting group to solubilize the material, enabling solution processing from green solvents. Post-deposition treatment of films via thermal annealing cleaves the protecting group yielding the known PDIN-H material, rendering films solvent-resistant. The PDIN-H films were characterized by optical absorption spectroscopy, contact angle measurements, and atomic force microscopy. When used to modify the surface of ZnO in inverted-type organic photovoltaics (air-processed and tested) based on the PM6:Y6 and PTQ10:Y6 bulk-heterojunctions, the device power conversion efficiency increases from 9.8 to 11.0% and 7.2 to 9.8%, respectively.

A Multi-modal Approach to Understanding Degradation of Organic Photovoltaic Materials.

State-of-the-art organic photovoltaic (OPV) materials are composed of complex, chemically diverse polymeric and molecular structures that form highly intricate solid-state interactions, collectively yielding exceptional tunability in performance and aesthetics. These properties are especially attractive for semitransparent power-generating windows or shades in living environments, greenhouses, or other architectural integrations. However, before such a future is realized, a broader and deeper understanding of property stability must be acquired. Stability during operating and environmental conditions is critical, namely, material color steadfastness, optoelectronic performance retention, morphological rigidity, and chemical robustness. To date, no single investigation encompasses all four distinct, yet interconnected, metrics. Here, we present a multimodal strategy that captures a dynamic and interconnected evolution of each property during the course of an accelerated photobleaching experiment. We demonstrate this approach across relevant length scales (from molecular to visual macroscale) using X-ray photoelectron spectroscopy, grazing-incidence X-ray scattering, microwave conductivity, and time-dependent photobleaching spectroscopies for two high-performance semitransparent OPV blends-PDPP4T:PC60BM and PDPP4T:IEICO-4F, with comparisons to the stabilities of the individual components. We present direct evidence that specific molecular acceptor (fullerene vs nonfullerene) designs and the resulting donor-acceptor interactions lead to distinctly different mechanistic routes that ultimately arrive at what is termed "OPV degradation." We directly observe a chemical oxidation of the cyano endcaps of the IEICO-4F that coincides with a morphological change and large loss in photoconductivity while the fullerene acceptor-containing blend demonstrates a significantly greater fraction of oxygen uptake but retains 55% of the photoconductivity. This experimental roadmap provides meaningful guidance for future high-throughput, multimodal studies, benchmarking the sensitivity of the different analytical techniques for assessing stability in printable active layers, independent of complete device architectures.

B.2.16 is a non-lethal modifier of the Dark82 mosaic eye phenotype in Drosophila melanogaster.

Genetic screens have been used to identify genes involved in the regulation of different biological processes. We identified growth mutants in a Flp/FRT screen using the Drosophila melanogaster eye to identify conditional regulators of cell growth and cell division. One mutant identified from this screen, B.2.16, was mapped and characterized by researchers in undergraduate genetics labs as part of the Fly-CURE. We find that B.2.16 is a non-lethal genetic modifier of the Dark82 mosaic eye phenotype.

Slot-Die-Coated Ternary Organic Photovoltaics for Indoor Light Recycling.

Efficient organic photovoltaics (OPVs) based on slot-die-coated (SD) ternary blends were developed for low-intensity indoor light harvesting. For active layers processed in air and from eco-friendly solvents, our device performances (under 1 sun and low light intensity) are the highest reported values for fluoro-dithiophenyl-benzothiadiazole donor polymer-based OPVs. The N-annulated perylene diimide dimer acceptor was incorporated into a blend of donor polymer (FBT) and fullerene acceptor (PC61BM) to give ternary bulk heterojunction blends. SD ternary-based devices under 1 sun illumination showed enhanced power conversion efficiency (PCE) from 6.8 to 7.7%. We observed enhancement in the short-circuit current density and open-circuit voltage of the devices. Under low light intensity light-emitting device illumination (ca. 2000 lux), the ternary-based devices achieved a PCE of 14.0% and a maximum power density of 79 µW/cm2 compared to a PCE of 12.0% and a maximum power density of 68 µW/cm2 for binary-based devices. Under the same illumination conditions, the spin-coated (SC) devices showed a PCE of 15.5% and a maximum power density of 88 µW/cm2. Collectively, these results demonstrate the exceptional promise of a SD ternary blend system for indoor light harvesting and the need to optimize active layers based on industry-relevant coating approaches toward mini modules.

Water Recovery from Advanced Water Purification Facility Reverse Osmosis Concentrate by Photobiological Treatment Followed by Secondary Reverse Osmosis.

Reverse osmosis (RO)-based desalination and advanced water purification facilities have inherent challenges associated with concentrate management and disposal. Although enhanced permeate recovery and concentrate minimization are desired, membrane scaling due to inorganic constituents, such as silica, calcium, phosphate, and iron, hinders the process. To solve this problem, a new diatom-based photobiological process has been developed to remove these scaling constituents by biological uptake and precipitation. In this study, RO concentrate samples were collected from a full-scale advanced water reclamation facility in California and were treated in 3.8 and 57 L photobioreactors inoculated with a brackish water diatom  Pseudostaurosira trainorii PEWL001 using light-emitting diode bulbs or natural sunlight as a light source. The photobiological treatment removed 95% of reactive silica and 64% of calcium and enabled additional water recovery using a secondary RO at a recovery rate up to 66%. This represents 95% overall recovery, including 85% recovery in the primary RO unit. In addition to the scaling constituents, the photobiological treatment removed 12 pharmaceuticals and personal care products, as well as N-nitrosodimethylamine, from RO concentrate samples primarily via photolysis. This novel approach has a strong potential for application to brackish water desalination and advanced water purification in arid and semiarid areas.

The Henry's constant of monochloramine.

Monochloramine is a secondary disinfectant used in drinking water and is also formed in chlorinated wastewater. While known to hydrolyze over time and react with dissolved organic matter, its partitioning between the aqueous and gas phase has not been extensively studied. Preliminary experiments demonstrated that monochloramine concentrations in solutions open to the atmosphere or actively aerated decreased more rapidly than in sealed solutions, indicating significant losses to the atmosphere. For example, a monochloramine solution open to the atmosphere yielded a loss rate constant of 0.08 d-1, a value twice that for sealed samples without headspace (0.04 d-1) where loss occurs exclusively as a result of hydrolysis. A solution aerated at 10 mL s-1 had a loss rate constant nearly 10× greater than that for hydrolysis alone (0.35 d-1). To better understand partitioning of monochloramine to the gas phase and potential for volatilization, the dimensionless Henry's law constants of monochloramine (KH) were determined using an equilibrium headspace technique at five different temperatures (11, 16, 21, 27, and 32 °C). The resulting values ranged from 8 × 10-3 to 4 × 10-2, indicating a semi-volatile compound, and were found to be consistent with quantitative structure activity relationship predictions. At 20 °C, monochloramine exhibits a dimensionless Henry's constant of about 1.7 × 10-2 which is 35 times greater than ammonia but comparable to the Henry's constant of inorganic semi-volatile compounds such sulfur dioxide. The Henry's constant values for monochloramine suggests that volatilization could be a relevant loss process in open systems such as rivers receiving chlorinated wastewater effluent, swimming pools and cooling towers.

Use of hydroacoustic measurements to characterize bottom sediments and guide sampling and remediation of organic contaminants in lake sediments.

Sampling of bed sediment for contamination characterization is often limited by the heterogeneity in sediment properties and distribution. In this study, we explored the use of hydroacoustic measurements to characterize sediment properties and guide sediment sampling in a small lake contaminated by organochlorine pesticides (OCPs) and PCBs. A dual frequency hydroacoustic survey was conducted to characterize sediment properties, distribution, and thickness in McGrath Lake, near Ventura, CA. Based upon these results, sediment core samples were collected from 15 sites on the lake, and sectioned into 20 cm intervals for sediment characterization and analysis of OCPs and PCBs. Very high concentrations of total DDT and total chlordane were found in the sediments, with mean values of 919 and 34.9 ng g(-1), respectively. Concentrations of OCPs were highest at 60-80 cm depth near the inflow at the north end of the lake. Total PCB concentrations were much lower (mean concentration of 4.5 ng g(-1)). Using the hydroacoustic and chemical data, it was estimated that nearly 30,000 m(3) of DDT- and chlordane-contaminated sediment (above effects range median values) was present in the uppermost 1.2 m of sediment in the lake. A hydroacoustic survey can be a valuable tool used to delineate sediment distribution in a lake, identify areas with deeper organic sediment where hydrophobic contaminants would likely be found, and guide sampling. Sampling and chemical analyses are nonetheless needed to quantify contaminant levels in bottom sediments. When combined with hydroacoustic measurements, this approach can reasonably estimate the distributions and volumes of contaminated sediment important in the development of remediation strategies.

Methane production and ebullition in a shallow, artificially aerated, eutrophic temperate lake (Lake Elsinore, CA).

Methane is an important component of the gases released from lakes. Understanding the factors influencing the release is important for mitigating this greenhouse gas. The volume of methane (CH4) and other gases in sediments, and the rate of CH4 ebullition, were determined for an artificially aerated, shallow, eutrophic freshwater lake in Southern California. Gas volume was measured at 28 sites in July 2010, followed by monthly sampling at 7 sites through December 2011. Gas volumes measured in July 2010 at the 28 sites exhibited a complex dependence on sediment properties; the volume of CH4 and other gases was negligible in very coarse-textured sediment with low water and organic carbon contents. Gas volumes increased strongly with increased silt content, and were highest in sediments with intermediate water contents (60 to 70%), organic carbon contents (2 to 3%) and depths (approximately 4m). Methane was the dominant gas collected from sediment (80 to 90%), while carbon dioxide comprised roughly 2 to 3% of sediment gas in the lake. Gas sampling during cool winter months revealed very low or undetectable volumes of gas present, while sediment gas volumes increased markedly during the spring and early summer months, and then declined in late summer and fall. The rate of CH4 ebullition, quantified with an echosounder, also varied markedly across the lake and seasonally. High rates of ebullition were measured at all 7 sites in July 2011 (up to 96mmolCH4m(-2)d(-1)), while the rates were >50% lower in September and negligible in December 2010. Ebullition rates were inversely correlated with depth and most other sediment properties, but strongly positively correlated with sand content. No simple relationship between ebullition rate and sediment gas volume across the set of sites was found, although ebullition rates at individual sites were strongly related to gas volume.

Regulation of dynein localization and centrosome positioning by Lis-1 and asunder during Drosophila spermatogenesis.

Dynein, a microtubule motor complex, plays crucial roles in cell-cycle progression in many systems. The LIS1 accessory protein directly binds dynein, although its precise role in regulating dynein remains unclear. Mutation of human LIS1 causes lissencephaly, a developmental brain disorder. To gain insight into the in vivo functions of LIS1, we characterized a male-sterile allele of the Drosophila homolog of human LIS1. We found that centrosomes do not properly detach from the cell cortex at the onset of meiosis in most Lis-1 spermatocytes; centrosomes that do break cortical associations fail to attach to the nucleus. In Lis-1 spermatids, we observed loss of attachments between the nucleus, basal body and mitochondria. The localization pattern of LIS-1 protein throughout Drosophila spermatogenesis mirrors that of dynein. We show that dynein recruitment to the nuclear surface and spindle poles is severely reduced in Lis-1 male germ cells. We propose that Lis-1 spermatogenesis phenotypes are due to loss of dynein regulation, as we observed similar phenotypes in flies null for Tctex-1, a dynein light chain. We have previously identified asunder (asun) as another regulator of dynein localization and centrosome positioning during Drosophila spermatogenesis. We now report that Lis-1 is a strong dominant enhancer of asun and that localization of LIS-1 in male germ cells is ASUN dependent. We found that Drosophila LIS-1 and ASUN colocalize and coimmunoprecipitate from transfected cells, suggesting that they function within a common complex. We present a model in which Lis-1 and asun cooperate to regulate dynein localization and centrosome positioning during Drosophila spermatogenesis.

Quantifying quagga mussel veliger abundance and distribution in Copper Basin Reservoir (California) using acoustic backscatter.

Quagga mussels (Dreissena bugensis) have been linked to oligotrophication of lakes, alteration of aquatic food webs, and fouling of infrastructure associated with water supply and power generation, causing potentially billions of dollars in direct and indirect damages. Understanding their abundance and distribution is key in slowing their advance, assessing their potential impacts, and evaluating effectiveness of control strategies. Volume backscatter strength (Sv) measurements at 201- and 430-kHz were compared with quagga mussel veliger and zooplankton abundances determined from samples collected using a Wisconsin closing net from the Copper Basin Reservoir on the Colorado River Aqueduct. The plankton within the lower portion of the water column (>18 m depth) was strongly dominated by D-shaped quagga mussel veligers, comprising up to 95-99% of the community, and allowed direct empirical measurement of their mean backscattering cross-section. The upper 0-18 m of the water column contained a smaller relative proportion of veligers based upon net sampling. The difference in mean volume backscatter strength at these two frequencies was found to decrease with decreasing zooplankton abundance (r(2) = 0.94), allowing for correction of Sv due to the contribution of zooplankton and the determination of veliger abundance in the reservoir. Hydroacoustic measurements revealed veligers were often present at high abundances (up to 100-200 ind L(-1)) in a thin 1-2 m layer at the thermocline, with considerable patchiness in their distribution observed along a 700 m transect on the reservoir. Under suitable conditions, hydroacoustic measurements can rapidly provide detailed information on the abundance and distribution of quagga mussel veligers over large areas with high horizontal and vertical resolution.

Characterization of bottom sediments in lakes using hydroacoustic methods and comparison with laboratory measurements.

The acoustical properties of bottom sediments in two lakes were shown to be strongly correlated with clay content, organic C and total N concentrations, and other important sediment properties. The fractal dimension of the bottom echo was more strongly correlated with sediment physical and chemical properties than energy-based measures. The fractal dimension was also related to rates of PO4-P and NH4-N release from intact sediment cores and sediment oxygen demand. Measurements made at 430-kHz were more sensitive to differences in sediment properties than 201- or 38-kHz. Hydroacoustic measurements allow rapid assessment of properties important in lake restoration and water resource management.

Aluminum polymers formed following alum treatment of lake water.

Alum (aluminum sulfate) is increasingly being used in lake management to control internal recycling of phosphorus from bottom sediments. Alum added to water undergoes rapid hydrolysis reactions, forming an amorphous Al(OH)3 floc with a high capacity for sorption of phosphorus. While it is known that the Al(OH)3 floc transforms over time to more ordered microcrystalline and crystalline gibbsite phases, there remains an incomplete understanding of the forms of Al present immediately following alum addition to lake water. A laboratory study was thus undertaken to evaluate the forms of Al present following alum addition using ferron (8-hydroxy-7-iodo-5-quinolinesulfonic acid) timed-colorimetric and 27Al-NMR measurements. A polymeric Al species with moderate reactivity with ferron (Alb2) was initially formed, although it rapidly transformed to a less ferron-reactive colloidal form (Alc) and also decomposed at low alum doses to monomeric Al (Ala) in response to pH increases associated with outgassing of CO2. The Ala fraction in these solutions could be adequately estimated based upon measured pH assuming Al solubility was controlled by an amorphous Al(OH)3 phase. Al13 was inferred from ferron measurements to be present, but only at quite low concentrations in the alum-treated waters.

Asunder is a critical regulator of dynein-dynactin localization during Drosophila spermatogenesis.

Spermatogenesis uses mitotic and meiotic cell cycles coordinated with growth and differentiation programs to generate functional sperm. Our analysis of a Drosophila mutant has revealed that asunder (asun), which encodes a conserved protein, is an essential regulator of spermatogenesis. asun spermatocytes arrest during prophase of meiosis I. Strikingly, arrested spermatocytes contain free centrosomes that fail to stably associate with the nucleus. Spermatocytes that overcome arrest exhibit severe defects in meiotic spindle assembly, chromosome segregation, and cytokinesis. Furthermore, the centriole-derived basal body is detached from the nucleus in asun postmeiotic spermatids, resulting in abnormalities later in spermatogenesis. We find that asun spermatocytes and spermatids exhibit drastic reduction of perinuclear dynein-dynactin, a microtubule motor complex. We propose a model in which asun coordinates spermatogenesis by promoting dynein-dynactin recruitment to the nuclear surface, a poorly understood process required for nucleus-centrosome coupling at M phase entry and fidelity of meiotic divisions.

Hydrogen sulfide production and volatilization in a polymictic eutrophic saline lake, Salton Sea, California.

The Salton Sea is a large shallow saline lake located in southern California that is noted for high sulfate concentrations, substantial algal productivity, and very warm water column temperatures. These conditions are well-suited for sulfide production, and sulfide has been implicated in summer fish kills, although no studies have been conducted to specifically understand hydrogen sulfide production and volatilization there. Despite polymictic mixing patterns and relatively short accumulation periods, the amount of sulfide produced is comparable to meromictic lakes. Sulfide levels in the Salton Sea reached concentrations of 1.2 mmol L(-1) of total free sulfide in the hypolimnion and 5.6 mmol L(-1) in the sediment pore water. Strong winds in late July mixed H2S into the surface water, where it depleted the entire water column of dissolved oxygen and reached a concentration of 0.1 mmol L(-1). Sulfide concentrations exceeded the toxicity threshold of tilapia (Oreochromis mossambicus) and combined with strong anoxia throughout the water column, resulted in a massive fish kill. The mixing of sulfide into the surface waters also increased atmospheric H2S concentrations, reaching 1.0 micromol m(-3). The flux of sulfide from the sediment into the water column was estimated to range from 2-3 mmol m(-2) day(-1) during the winter and up to 8 mmol m(-2) day(-1) during the summer. Application of the two-layer model for volatilization indicates that up to 19 mmol m(-2) day(-1) volatilized from the surface during the mixing event. We estimate that as much as 3400 Mg year(-1) or approximately 26% of sulfide that diffused into the water column from the deepest sediments may have been volatilized to the atmosphere.

Evaluation of two enzyme immunoassays for detection of Clostridium difficile toxins A and B in swine.

Diagnosis of Clostridium difficile-associated disease (CDAD) in neonatal pigs is accomplished, in part, by detection of toxins A (TcdA) and B (TcdB) in feces or colonic contents. Samples (n=115) were tested simultaneously with two toxin assays (Clostridium difficile Tox A/B II, TechLab, Blacksburg, VA; Gastro-tect Clostridium difficile Toxin A+B, Medical Chemical Corporation). Previous comparison of the Tox A/B II assay to the reference method (toxicity in CHO cell monolayers) revealed an overall correlation of 88%, with 91% sensitivity and 86% specificity, a positive predictive value of 86 and a negative predictive value of 84. In comparing the two EIAs, a group of nine samples were positive in both assays and a group of 92 were negative in both. However, 14 samples positive in the Tox A/B II were negative in the Gastro-tect assay. Thus, in comparison to the Tox A/B II assay, the Gastro-tect assay was 100% specific but only 39% sensitive. Its negative predictive value was 87, but its positive predictive value was 100. Thus, the Tox A/B II kit is apparently superior to the Gastro-tect Toxin A+B test for diagnosis of CDAD in neonatal pigs.

The role of collegial interaction in continuing professional development.

INTRODUCTION: Many physicians seek information from colleagues over other sources, highlighting the important role of interaction in continuing professional development (CPD). To guide the development of CPD opportunities, this study explored the nature of cancer-related questions faced by general surgeons, and how interaction with colleagues addressed those questions. METHODS: This study involved thematic analysis of field notes collected through observation and transcripts of telephone interviews with 20 surgeons, two pathologists, one medical oncologist, and one radiation oncologist affiliated with six community hospitals participating in multidisciplinary cancer conferences by videoconference in one region of Ontario, Canada. RESULTS: Six multidisciplinary cancer conferences (MCCs) were observed between April and September 2006, and 11 interviews were conducted between December 2006 and January 2007. Sharing of clinical experience made possible collective decision making for complex cancer cases. Physicians thought that collegial interaction improved awareness of current evidence, patient satisfaction with treatment plans, appropriate care delivery, and continuity. By comparing proposed treatment with that of the group and gaining exposure to decision making for more cases than they would see in their own practices, physicians developed clinical expertise that could be applied to future cases. Little collegial interaction occurred outside these organized sessions. DISCUSSION: These findings highlight the role of formally coordinated collegial interaction as an important means of CPD for general surgeons. Investment may be required for infrastructure to support such efforts and for release of health professional time for participation. Further research is required to examine direct and indirect outcomes of collegial interaction.

Stratification and mixing in Lake Elsinore, California: an assessment of axial flow pumps for improving water quality in a shallow eutrophic lake.

A 3-year study was conducted to quantify the effectiveness of a destratification system on weakening thermal stratification and increasing dissolved oxygen (DO) levels in Lake Elsinore, California. Biweekly measurements of temperature, DO, and other parameters were made at 14 sites across the lake beginning in July 2003. A destratification system consisting of 20 axial flow pumps fitted with 3 HP electric motors and 1.8m diameter impellers mounted 2m below the water surface was installed in the spring of 2004 and made fully operational in July 2004. An unusually wet winter of 2005 raised the summer mean depth from 3.0m in 2004 to 6.7 m in 2005. This study thus allowed us to quantify the influence of axial flow pump operation on water column properties under shallow water conditions (i.e., before and after axial flow pump installation), and also to compare the effectiveness of the destratification system at two strongly different lake levels. Transparencies increased substantially after the winter storms in 2005 and thermal stability was shown to be strongly dependent upon lake level. Stratification and a large area of anoxic sediments persisted despite pump operation in the summers of 2004 and 2005. Acoustic Doppler current profiler (ADCP) measurements showed that mixing energy was not being efficiently transmitted laterally into the water column.

Prevention of porcine Clostridium difficile-associated disease by competitive exclusion with nontoxigenic organisms.

Clostridium difficile is widely known as a cause of disease in humans, and has emerged as an important problem in neonatal swine. No commercial product is available for immunoprophylaxis of C. difficile-associated disease, but success in preventing experimental infections in hamsters by use of nontoxigenic strains to competitively exclude toxigenic strains led us to try this method in neonatal pigs. Spores were administered orally to newborn pigs or were sprayed onto perineum and teats of dams. Significantly more piglets were weaned among litters receiving spores orally, and average weaning weights were significantly higher for both treatment groups than for controls. Toxins A and B were detected in 44.8% of litters and 16.5% of piglets born to sprayed sows and 58.3% of litters and 15.4% of piglets in the control group. However, toxins were detected in only 13.8% of litters and 3.4% of piglets given spores orally. These data support a contention that precolonization by a nontoxigenic strain can ameliorate the pre-weaning growth retardation associated with C. difficile infection in piglets.