Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks.

Some infectious diseases, including COVID-19, can undergo airborne transmission. This may happen at close proximity, but as time indoors increases, infections can occur in shared room air despite distancing. We propose two indicators of infection risk for this situation, that is, relative risk parameter (Hr) and risk parameter (H). They combine the key factors that control airborne disease transmission indoors: virus-containing aerosol generation rate, breathing flow rate, masking and its quality, ventilation and aerosol-removal rates, number of occupants, and duration of exposure. COVID-19 outbreaks show a clear trend that is consistent with airborne infection and enable recommendations to minimize transmission risk. Transmission in typical prepandemic indoor spaces is highly sensitive to mitigation efforts. Previous outbreaks of measles, influenza, and tuberculosis were also assessed. Measles outbreaks occur at much lower risk parameter values than COVID-19, while tuberculosis outbreaks are observed at higher risk parameter values. Because both diseases are accepted as airborne, the fact that COVID-19 is less contagious than measles does not rule out airborne transmission. It is important that future outbreak reports include information on masking, ventilation and aerosol-removal rates, number of occupants, and duration of exposure, to investigate airborne transmission.

Can indoor sports centers be allowed to re-open during the COVID-19 pandemic based on a certificate of equivalence?

Within a time span of only a few months, the SARS-CoV-2 virus has managed to spread across the world. This virus can spread by close contact, which includes large droplet spray and inhalation of microscopic droplets, and by indirect contact via contaminated objects. While in most countries, supermarkets have remained open, due to the COVID-19 pandemic, authorities have ordered many other shops, restaurants, bars, music theaters and indoor sports centers to be closed. As part of COVID-19 (semi)lock-down exit strategies, many government authorities are now (May-June 2020) allowing a gradual re-opening, where sometimes indoor sport centers are last in line to be permitted to re-open. This technical note discusses the challenges in safely re-opening these facilities and the measures already suggested by others to partly tackle these challenges. It also elaborates three potential additional measures and based on these additional measures, it suggests the concept of a certificate of equivalence that could allow indoor sports centers with such a certificate to re-open safely and more rapidly. It also attempts to stimulate increased preparedness of indoor sports centers that should allow them to remain open safely during potential next waves of SARS-CoV-2 as well as future pandemics. It is concluded that fighting situations such as the COVID-19 pandemic and limiting economic damage requires increased collaboration and research by virologists, epidemiologists, microbiologists, aerosol scientists, building physicists, building services engineers and sports scientists.

Size and mineral composition of airborne particles generated by an ultrasonic humidifier.

This study describes the size distribution and concentration of particles expelled by a portable, 3-L ultrasonic humidifier. The ultrasonic humidifier was filled with waters of varying mineral content and hardness. Aerosol size distributions were measured during 8 hours of humidifier operation in a typical bedroom. Humidifiers produced approximately 1.22 × 1010 -2.50 × 1010 airborne particles per milliliter of water consumed, resulting in airborne particle concentrations of 3.01-5.91 × 104  #/cm3 , with modes ranging between 109 and 322 nm in diameter. The emission rate of particles varied by water type from 1.02 × 109 to 2.27 × 109  #/s. Lower mineral waters produced fewer, smaller particles when compared to higher mineral waters. Chemical analyses of particles collected with a cascade impactor indicated that the minerals in emitted particles had the same relative mineral concentrations as the fill water. Our results demonstrate that ultrasonic humidifiers should be considered a source of inhalation exposure to minerals dissolved in water, and that the magnitude of exposure to inhalable particles will vary with water quality.

A simple method to measure the gas-phase SVOC concentration adjacent to a material surface.

Assessing human exposure to semivolatile organic compounds (SVOCs) emitted from materials and products is difficult because methods are not available to easily measure the key emission parameters. A simple method based on a passive sampling technique was thus developed to measure the gas-phase SVOC concentration (y0 ) immediately adjacent to the material surface in a consumer product. The method employs standard stainless steel thermal desorption tubes, with values of y0 and an additional unknown parameter, K, the tube surface/air partition coefficient inside the desorption tube, obtained by fitting a diffusion model to the sampling data. Phthalates in two types of polyvinyl chloride flooring were selected to test the method. The values of y0 and K agree well with those measured in independent chamber tests. The y0 measurement method is shown to be applicable to chemicals with a wide range of vapor pressures. This novel method should be useful for assessing potential exposure to SVOCs in consumer products as well as for exposure-based prioritization of chemicals and their associated products in indoor environments.

Simulation of vertical concentration gradient of influenza viruses in dust resuspended by walking.

UNLABELLED: Particles are resuspended from the floor by walking and are subject to turbulent transport in the human aerodynamic wake. These processes may generate a vertical concentration gradient of particles. To estimate the magnitude of turbulence generated by walking, we measured the velocity field in the wake from floor to ceiling at 10-cm intervals with a sonic anemometer. The resulting eddy diffusion coefficients varied between 0.06 and 0.20 m(2) /s and were maximal at ~0.75-1 m above the floor, approximately the height of the swinging hand. We applied the eddy diffusion coefficients in an atmospheric transport model to predict concentrations of resuspended influenza virus as a function of the carrier particle size, height in the room, and relative humidity, which affects the resuspension rate coefficient and virus viability. Results indicated that the concentration of resuspended viruses at 1 m above the floor was up to 40% higher than at 2 m, depending on particle size. For exposure to total resuspended viruses, the difference at 1 vs. 2 m was 11-14%. It is possible that shorter people are exposed to higher concentrations of resuspended dust, including pathogens, although experimental evidence is needed to verify this proposition. PRACTICAL IMPLICATIONS: Forces generated by walking can resuspend particles from the floor and create higher concentrations close to the floor and lower concentrations above it. These particles may include pathogens, such as the influenza virus, that were previously emitted into the air by an infected individual and that settled to the ground. Due to particle resuspension and turbulent transport, it is possible that shorter people are exposed to higher concentrations of particles, including certain pathogens, than are taller people. This work could be used in support of epidemiological investigations into the incidence of influenza as a function of a person's height and to guide the design of more effective control strategies to reduce transmission of influenza.

Immunology in the clinic review series; focus on cancer: double trouble for tumours: bi-functional and redirected T cells as effective cancer immunotherapies.

Cancer is one of the most important pathological conditions facing mankind in the 21st century, and is likely to become the most important cause of death as improvements continue in health, diet and life expectancy. The immune response is responsible for controlling nascent cancer through immunosurveillance. If tumours escape this control, they can develop into clinical cancer. Although surgery and chemo- or radiotherapy have improved survival rates significantly, there is a drive to reharness immune responses to treat disease. As T cells are one of the key immune cells in controlling cancer, research is under way to enhance their function and improve tumour targeting. This can be achieved by transduction with tumour-specific T cell receptor (TCR) or chimaeric antigen receptors (CAR) to generate redirected T cells. Virus-specific cells can also be transduced with TCR or CAR to create bi-functional T cells with specificity for both virus and tumour. In this review we outline the development and optimization of redirected and bi-functional T cells, and outline the results from current clinical trials using these cells. From this we discuss the challenges involved in generating effective anti-tumour responses while avoiding concomitant damage to normal tissues and organs.

How did we get here: what are droplets and aerosols and how far do they go? A historical perspective on the transmission of respiratory infectious diseases.

The COVID-19 pandemic has exposed major gaps in our understanding of the transmission of viruses through the air. These gaps slowed recognition of airborne transmission of the disease, contributed to muddled public health policies and impeded clear messaging on how best to slow transmission of COVID-19. In particular, current recommendations have been based on four tenets: (i) respiratory disease transmission routes can be viewed mostly in a binary manner of 'droplets' versus 'aerosols'; (ii) this dichotomy depends on droplet size alone; (iii) the cut-off size between these routes of transmission is 5 µm; and (iv) there is a dichotomy in the distance at which transmission by each route is relevant. Yet, a relationship between these assertions is not supported by current scientific knowledge. Here, we revisit the historical foundation of these notions, and how they became entangled from the 1800s to today, with a complex interplay among various fields of science and medicine. This journey into the past highlights potential solutions for better collaboration and integration of scientific results into practice for building a more resilient society with more sound, far-sighted and effective public health policies.

Dismantling myths on the airborne transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2).

The coronavirus disease 2019 (COVID-19) pandemic has caused untold disruption throughout the world. Understanding the mechanisms for transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is key to preventing further spread, but there is confusion over the meaning of 'airborne' whenever transmission is discussed. Scientific ambivalence originates from evidence published many years ago which has generated mythological beliefs that obscure current thinking. This article collates and explores some of the most commonly held dogmas on airborne transmission in order to stimulate revision of the science in the light of current evidence. Six 'myths' are presented, explained and ultimately refuted on the basis of recently published papers and expert opinion from previous work related to similar viruses. There is little doubt that SARS-CoV-2 is transmitted via a range of airborne particle sizes subject to all the usual ventilation parameters and human behaviour. Experts from specialties encompassing aerosol studies, ventilation, engineering, physics, virology and clinical medicine have joined together to produce this review to consolidate the evidence for airborne transmission mechanisms, and offer justification for modern strategies for prevention and control of COVID-19 in health care and the community.

Profilin and the Abl tyrosine kinase are required for motor axon outgrowth in the Drosophila embryo.

The ability of neuronal growth cones to be guided by extracellular cues requires intimate communication between signal transduction systems and the dynamic actin-based cytoskeleton at the leading edge. Profilin, a small, actin-binding protein, has been proposed to be a regulator of the cell motility machinery at leading edge membranes. However, its requirement in the developing nervous system has been unknown. Profilin associates with members of the Enabled family of proteins, suggesting that Profilin might link Abl function to the cytoskeleton. Here, genetic analysis in Drosophila is used to demonstrate that mutations in Profilin (chickadee) and Abl (abl) display an identical growth cone arrest phenotype for axons of intersegmental nerve b (ISNb). Moreover, the phenotype of a double mutant suggests that these components function together to control axonal outgrowth.

Tumor-associated antigens in cervical cancer tissues and in sera from patients with cervical cancer or with head and neck cancer.

Hyperimmune New Zealand White rabbit sera prepared against partially purified tumor-associated antigens (TAA) of invasive cervical cancer tissues (CaCx's) were used to demonstrate TAA in CaCx's and circulating TAA (C-TAA) in sera from patients with cervical cancer or with head and neck cancer. Anti-CaCx serum adsorbed with pooled normal cervical tissue (NCx) antigen preparations and with lyophilized pooled normal human plasma gave precipitin in gel reactions with CaCx but not with NCx, which indicated the presence of TAA in CaCx. The adsorbed antisera reacted with sera from patients with cervical and head and neck cancers, which indicated the presence of C-TAA in such sera. False-positive reactions with control sera from normal humans or from patients with benign gynecologic diseases were much less frequently observed. Statistical analysis of data obtained by the testing of 96 coded serum samples from the National Cancer Institute-Mayo Clinic Serum Bank (Rochester, Minn.) revealed that the results were significant and that specificity was high but sensitivity of the assay was relatively low.

Sequence of the region coding for virion proteins C and E2 and the carboxy terminus of the nonstructural proteins of rubella virus: comparison with alphaviruses.

The sequence of the 3' 4508 nucleotides (nt) of the genomic RNA of the Therien strain of rubella virus (RV) was determined for cDNA clones. The sequence contains a 3189-nt open reading frame (ORF) which codes for the structural proteins C, E2 and E1. C is predicted to have a length of 300 amino acids (aa). The N-terminal half of the C protein is highly basic and hydrophilic in nature, and is putatively the region of the protein which interacts with the virion RNA. At the C terminus of the C protein is a stretch of 20 hydrophobic aa which also serves as the signal sequence for E2, indicating that the cleavage of C from the polyprotein precursor may be catalyzed by signalase in the lumen of the endoplasmic reticulum. E2 is 282 aa in length and contains four potential N-linked glycosylation sites and a putative transmembrane domain near its C terminus. The sequence of E1 has been previously described [Frey et al., Virology 154 (1986) 228-232]. No homology could be detected between the amino acid sequence of the RV structural proteins and the amino acid sequence of the alphavirus structural proteins. From the position of a region of 30 nt in the RV genomic sequence which exhibited significant homology with the sequence in the alphavirus genome at which subgenomic RNA synthesis is initiated, the RV subgenomic RNA is predicted to be 3346 nt in length and the nontranslated region from the 5' end of the subgenomic RNA to the structural protein ORF is predicted to be 98 nt. In a different translation frame beginning at the 5' end of the RV nt sequence reported here is a 1407 nt ORF which is the C terminal region of the nonstructural protein ORF. This ORF overlaps the structural protein ORF by 149 nt. A low level of homology could be detected between the predicted amino acid sequence of the C-terminus of the RV nonstructural protein ORF and the replicase proteins of several positive RNA viruses of animals and plants, including nsp4 of the alphaviruses, the protein encoded by the C-terminal region of the alphavirus nonstructural ORF. However, the overall homology between RV and the alphaviruses in this region of the genome was only 18%, indicating that these two genera of the Togavirus family are only distantly related. Intriguingly, there is a 2844-nt ORF present in the negative polarity orientation of the RV sequence which could encode a 928-aa polyprotein.

Analysis of differential display RT-PCR products using fluorescent primers and GENESCAN software.

Differential display reverse transcription PCR (DDRT-PCR) is a procedure used to identify the induction or repression of gene expression. In most DDRT-PCR protocols, radioisotopes are incorporated during PCR and the cDNA products are detected by autoradiography. This report describes the fluorescent labeling of cDNAs and their detection on automated sequencers from PE Applied Biosystems. A fluorescent tag can be incorporated into the PCR product by using either a labeled primer or a labeled dUTP. The fluorescent signals are analyzed by GENESCAN software. Fluorescent DDRT-PCR increases throughput and obviates the handling of hazardous radioisotopes. A PCR cycling profile, expected to give improved reproducibility, is also described. Because amplified cDNAs can't be recovered from the automated sequencer gel, suggestions are given for the identification and recovery of differentially expressed cDNAs.

Sexual behavior in male rhesus monkeys elicited by electrical stimulation of preoptic and hypothalamic areas.

Electrical stimulation of the preoptic area, lateral hypothalamus or dorsomedial nucleus of the hypothalamus (DMH) has produced sexual behavioral responses in 11 male rhesus monkeys. At a short latency following the onset of each train of stimulation, the stimulated males would mount estrogen-treated, receptive females. Quantitative measures of the elicited sexual behavior, in 4 males, were applied to describe differences between the effect of preoptic and DMH stimulation on male sexual performance. As compared to spontaneous sexual activity, stimulation of the DMH produced mounts of longer duration, with more thrusts per mount, higher thrusting rates and a greater number of ejaculations per test session; refractory periods between successive ejaculatory episodes were shortened as a result of stimulation-induced mounting behavior. Preoptic stimulation also induced mounts of longer than normal duration characterized by a slightly increased number of thrusts per mount. In contrast to DMH stimulus effects, however, thrusting rate was decreased significantly by preoptic stimulation and ejaculation did not occur even after multiple stimulus-induced mounts. Penile erections were elicited by stimulation of the anterior hypothalamus, ventromedial nucleus and the posterior hypothalamus in socially isolated or restrained males; however, stimulation of these same sites was ineffective for provoking sexual behavioral responses when tests were performed while the males were paired with receptive females.

Diurnal variations of serum testosterone levels in intact and gonadectomized male and female rhesus monkeys.

A radioimmunoassay for serum testosterone which does not require chromatographic separation was used to measure the diurnal variations in intact and orchidecomized males and intact and ovariectomized females. The intact male rhesus monkey shows a distinctive diurnal variation in serum levels of testosterone characterized by lower values during the day and a marked increase in the early evening (1900-2200 hr). The testosterone levels remain high throughout most of the lights-off period in the intact male. In contrast to the intact male, the markedly lowered serum levels of testosterone in the orchidectomized male were higher during the day and consistently showed a nadir during the early evening (2000-2200 hr). The evening nadir of testosterone levels was 51.0% lower than the 24-hr mean whereas the maximum serum level was 46.4% higher. A similar circadian pattern of testosterone was seen in both the intact and ovariectomized females. The testosterone values were higher during the day and consistently showed a nadir during the early evening. These results suggest that the adrenal secretion of testosterone varies in a diurnal pattern characterized by an early evening nadir. This adrenal pattern is overshadowed by a much larger gonadal rhythm in the intact male.

Reducing the risk of accidental death due to vehicle-related carbon monoxide poisoning.

Emissions of carbon monoxide (CO) from motor vehicles cause several hundred accidental fatal poisonings annually in the United States. The circumstances that could lead to fatal poisonings in residential settings with motor vehicles as the source of CO were explored. The risk of death in a garage (volume = 90 m3) and a single-family dwelling (400 m3) was evaluated using a Monte Carlo simulation with varying CO emission rates and ventilation rates. Information on emission rates was obtained from a survey of motor vehicle exhaust gas composition under warm idle conditions in California, and information on ventilation rates was obtained from a summary of published measurements in the U.S. housing stock. The risk of death ranged from 16 to 21% for a 3-hr exposure in a garage to 0% for a 1-hr exposure in a house. Older vehicles were associated with a disproportionately high risk of death. Removing all pre-1975 vehicles from the fleet would reduce the risk of death by one-fourth to two-thirds, depending on the exposure scenario. Significant efforts have been made to control CO emissions from motor vehicles with the goal of reducing CO concentrations in outdoor air. Substantial public health benefit could also be obtained if vehicle control measures were designed to take account of acute CO poisonings explicitly.

Innate recognition of apoptotic cells: novel apoptotic cell-associated molecular patterns revealed by crossreactivity of anti-LPS antibodies.

Cells dying by apoptosis are normally cleared by phagocytes through mechanisms that can suppress inflammation and immunity. Molecules of the innate immune system, the pattern recognition receptors (PRRs), are able to interact not only with conserved structures on microbes (pathogen-associated molecular patterns, PAMPs) but also with ligands displayed by apoptotic cells. We reasoned that PRRs might therefore interact with structures on apoptotic cells - apoptotic cell-associated molecular patterns (ACAMPs) - that are analogous to PAMPs. Here we show that certain monoclonal antibodies raised against the prototypic PAMP, lipopolysaccharide (LPS), can crossreact with apoptotic cells. We demonstrate that one such antibody interacts with a constitutively expressed intracellular protein, laminin-binding protein, which translocates to the cell surface during apoptosis and can interact with cells expressing the prototypic PRR, mCD14 as well as with CD14-negative cells. Anti-LPS cross reactive epitopes on apoptotic cells colocalised with annexin V- and C1q-binding sites on vesicular regions of apoptotic cell surfaces and were released associated with apoptotic cell-derived microvesicles (MVs). These results confirm that apoptotic cells and microbes can interact with the immune system through common elements and suggest that anti-PAMP antibodies could be used strategically to characterise novel ACAMPs associated not only with apoptotic cells but also with derived MVs.

402AX teratocarcinoma MHC class I antigen expression is regulated in vivo by Lyt 1, Lyt 2, and L3T4 expressing splenic T cells.

The murine 402AX teratocarcinoma is a MHC class I antigen negative tumor of 129 strain origin. Host resistance to the 402AX tumor is genetically controlled. When passed intraperitoneally in genetically resistant mice, the tumor cells are induced to express MHC Class I antigens of the 129 genotype. When passed in genetically susceptible mice, the tumor cells remain MHC class I antigen negative. Earlier studies have demonstrated that resistance to the tumor and regulation of tumor cell MHC class I antigen expression are under the control of the host's immune system. The present studies indicate that splenic Lyt 1-, Lyt 2-, and L3T4-expressing cells regulate tumor cell MHC class I antigen expression, and that these cells require a genetically resistant host environment in which to differentiate. Splenic T cells primed to the 402AX tumor and transferred into genetically susceptible 129 mice give rise to GVHD, suggesting that immunity to the tumor involves reactivity to 129 minor histocompatibility antigens.

Effects of diabetes and insulin treatment on sorbitol and water of rat lenses.

Since increased lens sorbitol and osmotic swelling are central causative features of cataract in diabetic rats, the effects of insulin treatment on lens sorbitol, water, sodium, and potassium were studied. The sorbitol concentration in early stage diabetic lenses was greater than in normal ones by 83 mmol/kg water, and the lens water was greater by 1.3%. Sodium was greater by 9 mmol/kg water; potassium was less by the same amount so that the sum of sodium and potassium was not different. In insulin-treated diabetic lenses, the sorbitol was less than in untreated diabetic lenses by 39 mmol/kg water, and the lens water was not different. Insulin restored the potassium, but not the sodium, to normal concentration so that the sum of sodium and potassium was greater by 16 mmol/kg water. The differences in lens water were less than would be expected on the basis of osmosis due to differences in sorbitol and suggested that the lenses were able to maintain their water content within a narrow range by losing or gaining solutes to offset the differences in sorbitol.