Indicators for Risk of Airborne Transmission in Shared Indoor Environments and their application to COVID-19 Outbreaks

Some infectious diseases, including COVID-19, can be transmitted via aerosols that are emitted by an infectious person and inhaled by susceptible individuals. Most airborne transmission occurs at close proximity and is effectively reduced by physical distancing, but as time indoors increases, infections occur in those sharing room air despite maintaining distancing. There have been calls for quantified models to estimate the absolute and relative contribution of these different factors to infection risk. We propose two indicators of infection risk for this situation, i.e., 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 particulate air cleaning rates, number of occupants, and duration of exposure. COVID-19 outbreaks show a clear trend in relation to these factors that is consistent with airborne infection The observed trends of outbreak size (attack rate) vs. H (Hr) allow us to recommend values of these parameters to minimize COVID-19 indoor infection risk. Transmission in typical pre-pandemic indoor spaces is highly sensitive to mitigation efforts. Previous outbreaks of measles, flu, and tuberculosis were assessed along with recently reported COVID-19 outbreaks. Measles outbreaks occur at much lower risk parameter values than COVID-19, while tuberculosis outbreaks are observed at much higher risk parameter values. Since 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 the nature and type of masking, ventilation and particulate-air cleaning rates, number of occupants, and duration of exposure, to allow us to understand the circumstances conducive to airborne transmission of different diseases. SynopsisWe propose two infection risk indicators for indoor spaces and apply them to COVID-19 outbreaks analysis and mitigation.

Transmission Dynamics of Coronavirus Disease 2019 (COVID-19) in the World: The Roles of Intervention and Seasonality

The coronavirus disease 2019 (COVID-19) is spreading rapidly all over the world. The transmission dynamics of the COVID-19 pandemic is still unclear, but developing strategies for mitigating the severity of the pandemic is yet a top priority for global public health. In this study, we developed a novel compartmental model, SEIR-CV(susceptible-exposed-infectious-removed with control variables), which not only considers the key characteristics of asymptomatic infection and the effects of seasonal variations, but also incorporates different control measures for multiple transmission routes, so as to accurately predict and effectively control the spread of COVID-19. Based on SEIR-CV, we predicted the COVID-19 epidemic situation in China out of Hubei province and proposed corresponding control strategies. The results showed that the prediction results are highly consistent with the outbreak surveillance data, which proved that the proposed control strategies have achieved sound consequent in the actual epidemic control. Subsequently, we have conducted a rolling prediction for the United States, Brazil, India, five European countries (the United Kingdom, Italy, Spain, Germany, and France), southern hemisphere, northern hemisphere, and the world out of China. The results indicate that control measures and seasonal variations have a great impact on the progress of the COVID-19 pandemic. Our prediction results show that the COVID-19 pandemic is developing more rapidly due to the impact of the cold season in the southern hemisphere countries such as Brazil. While the development of the pandemic should have gradually weakened in the northern hemisphere countries with the arrival of the warm season, instead of still developing rapidly due to the relative loose control measures such as the United States and India. Furthermore, the prediction results illustrate that if keeping the current control measures in the main COVID-19 epidemic countries, the pandemic will not be contained and the situation may eventually turn to group immunization, which would lead to the extremely severe disaster of about 5 billion infections and 300 million deaths globally. However, if Chinas super stringent control measures were implemented from 15 July, 15 August or 15 September 2020, the total infections would be contained about 15 million, 32 million or 370 million respectively, which indicates that the stringent and timely control measures is critical, and the best window period is before September for eventually overcoming COVID-19. SignificanceCOVID-19 is now posing a huge threat to global public health. The key features such as asymptomatic infection and droplet or airborne transmission make COVID-19 more easily spread and more widely distributed around the world. It is an urgent need to explore the optimal intervention strategies and measures to contain the pandemic. Our novel SEIR-CV compartmental model considers the new features of COVID-19, exhibits the impact of the intervention strategies and seasonal variations, and thus can accurately predicts its trajectory in China and the rest of the world. Our research results suggest that control measures and seasonal variations have a great impact on the development of the COVID-19 pandemic, which can only be contained by stringent strategies during the best window period before September 2020 for eventually overcoming COVID-19, otherwise it would cause a severer global catastrophe.

Evidence for probable aerosol transmission of SARS-CoV-2 in a poorly ventilated restaurant

BackgroundThe role of aerosols in the transmission of SARS-CoV-2 remains debated. We analysed an outbreak involving three non-associated families in Restaurant X in Guangzhou, China, and assessed the possibility of aerosol transmission of SARS-CoV-2 and characterize the associated environmental conditions. MethodsWe collected epidemiological data, obtained a video record and a patron seating-arrangement from the restaurant, and measured the dispersion of a warm tracer gas as a surrogate for exhaled droplets from the suspected index patient. Computer simulations were performed to simulate the spread of fine exhaled droplets. We compared the in-room location of subsequently infected cases and spread of the simulated virus-laden aerosol tracer. The ventilation rate was measured using the tracer decay method. ResultsThree families (A, B, C), 10 members of which were subsequently found to have been infected with SARS-CoV-2 at this time, or previously, ate lunch at Restaurant X on Chinese New Years Eve (January 24, 2020) at three neighboring tables. Subsequently, three members of family B and two members of family C became infected with SARS-CoV-2, whereas none of the waiters or 68 patrons at the remaining 15 tables became infected. During this occasion, the ventilation rate was 0.75-1.04 L/s per person. No close contact or fomite contact was observed, aside from back-to-back sitting by some patrons. Our results show that the infection distribution is consistent with a spread pattern representative of exhaled virus-laden aerosols. ConclusionsAerosol transmission of SARS-CoV-2 due to poor ventilation may explain the community spread of COVID-19.

Multi-route respiratory infection: when a transmission route may dominate

The exact transmission route of many respiratory infectious diseases remains a subject for debate to date. The relative contribution ratio of each transmission route is largely undetermined, which is affected by environmental conditions, human behavior, the host and the microorganism. In this study, a detailed mathematical model is developed to investigate the relative contributions of different transmission routes to a multi-route transmitted respiratory infection. It is illustrated that all transmission routes can dominate the total transmission risk under different scenarios. Influential parameters considered include dose-response rate of different routes, droplet governing size that determines virus content in droplets, exposure distance, and virus dose transported to the hand of infector. Our multi-route transmission model provides a comprehensive but straightforward method to evaluate the transmission efficiency of different transmission routes of respiratory diseases and provides a basis for predicting the impact of individual level intervention methods such as increasing close-contact distance and wearing protective masks. (Word count: 153) HighlightsO_LIA multi-route transmission model is developed by considering evaporation and motion of respiratory droplets with the respiratory jet and consequent exposure of the susceptible. C_LIO_LIWe have illustrated that each transmission route may dominate during the influenza transmission, and the influential factors are revealed. C_LIO_LIThe short-range airborne route and infection caused by direct inhalation of medium droplets are highlighted. C_LI

Toilets dominate environmental detection of SARS-CoV-2 virus in a hospital

BackgroundRespiratory and faecal aerosols play a suspected role in transmitting the SARS-CoV-2 virus. We performed extensive environmental sampling in a dedicated hospital building for Covid-19 patients in both toilet and non-toilet environments, and analysed the associated environmental factors. MethodsWe collected data of the Covid-19 patients. 107 surface samples, 46 air samples, two exhaled condensate samples, and two expired air samples were collected were collected within and beyond the four three-bed isolation rooms. We reviewed the environmental design of the building and the cleaning routines. We conducted field measurement of airflow and CO2 concentrations. FindingsThe 107 surface samples comprised 37 from toilets, 34 from other surfaces in isolation rooms (ventilated at 30-60 L/s), and 36 from other surfaces outside isolation rooms in the hospital. Four of these samples were positive, namely two ward door-handles, one bathroom toilet-seat cover and one bathroom door-handle; and three were weakly positive, namely one bathroom toilet seat, one bathroom washbasin tap lever and one bathroom ceiling-exhaust louvre. One of the 46 air samples was weakly positive, and this was a corridor air sample. The two exhaled condensate samples and the two expired air samples were negative. InterpretationThe faecal-derived aerosols in patients toilets contained most of the detected SARS-CoV-2 virus in the hospital, highlighting the importance of surface and hand hygiene for intervention. FundingThe work were partially supported by the National Natural Science Foundation of China (no 41977370), the Research Grants Council of Hong Kongs (no 17202719) (no C7025-16G), and Scientific Research Fund of Jiangsu Provincial Department of Health (no S21017002).

Indoor transmission of SARS-CoV-2

BackgroundBy early April 2020, the COVID-19 pandemic had infected nearly one million people and had spread to nearly all countries worldwide. It is essential to understand where and how SARS-CoV-2 is transmitted. MethodsCase reports were extracted from the local Municipal Health Commissions of 320 prefectural cities (municipalities) in China, not including Hubei province, between 4 January and 11 February 2020. We identified all outbreaks involving three or more cases and reviewed the major characteristics of the enclosed spaces in which the outbreaks were reported and associated indoor environmental issues. ResultsThree hundred and eighteen outbreaks with three or more cases were identified, involving 1245 confirmed cases in 120 prefectural cities. We divided the venues in which the outbreaks occurred into six categories: homes, transport, food, entertainment, shopping, and miscellaneous. Among the identified outbreaks, 53{middle dot}8% involved three cases, 26{middle dot}4% involved four cases, and only 1{middle dot}6% involved ten or more cases. Home outbreaks were the dominant category (254 of 318 outbreaks; 79{middle dot}9%), followed by transport (108; 34{middle dot}0%; note that many outbreaks involved more than one venue category). Most home outbreaks involved three to five cases. We identified only a single outbreak in an outdoor environment, which involved two cases. ConclusionsAll identified outbreaks of three or more cases occurred in an indoor environment, which confirms that sharing indoor space is a major SARS-CoV-2 infection risk. FundingThe work was supported by the Research Grants Council of Hong (no 17202719, C7025-16G), and National Natural Science Foundation of China (no 41977370).

Short-range airborne route dominates exposure of respiratory infection during close contact

A susceptible person experiences the highest exposure risk of respiratory infection when he or she is in close proximity with an infected person. The large droplet route has been commonly believed to be dominant for most respiratory infections since the early 20th century, and the associated droplet precaution is widely known and practiced in hospitals and in the community. The mechanism of exposure to droplets expired at close contact, however, remains surprisingly unexplored. In this study, the exposure to exhaled droplets during close contact (< 2 m) via both the short-range airborne and large droplet sub-routes is studied using a simple mathematical model of expired flows and droplet dispersion/deposition/inhalation, which enables the calculation of exposure due to both deposition and inhalation. The short-range airborne route is found to dominate at most distances studied during both talking and coughing. The large droplet route only dominates when the droplets are larger than 100 m and when the subjects are within 0.2 m while talking or 0.5 m while coughing. The smaller the exhaled droplets, the more important the short-range airborne route. The large droplet route contributes less than 10% of exposure when the droplets are smaller than 50 m and when the subjects are more than 0.3 m apart, even while coughing. Practical implicationsOur simple but novel analysis shows that conventional surgical masks are not effective if most infectious viruses are contained in fine droplets, and non-conventional intervention methods such as personalised ventilation should be considered as infection prevention strategies given the possible dominance of the short-range airborne route, although further clinical evidence is needed. NomenclatureO_ST_ABSSubscriptC_ST_ABSi Droplets of different diameter groups (i = 1, 2, ..., N) LD Large droplet route SR Short-range airborne route SymbolsA0 Area of source mouth [m2] AE Aspiration efficiency [-] Ar0 Archimedes number [-] bg Gaussian half width [m] bt Top-hat half width [m] CD Drag coefficient [-] CI Specific heat of liquid [J*kg-1*K-1] Cs Specific heat of solid [J*kg-1*K-1] CT Correction factor for diffusion coefficient due to temperature dependence [-] dd Droplet diameter [m] dd0 Droplet initial diameter [m] de1 Major axis of eye ellipse [m] de2 Minor axis of eye ellipse [m] dh Characteristic diameter of human head [m] dm Mouth diameter [m] dn Nostril diameter [m] D{infty} Binary diffusion coefficient far from droplet [m2*s-1] DE Deposition efficiency [-] eLD Exposure due to large droplet route [L] eSR Exposure due to short-range airborne route [L] g Gravitational acceleration [m*s-2] Iv Mass current [kg*s-1] IF Inhalation fraction [-] Kc Constant (=0.3) [-] Kg Thermal conductivity of air [W*m-1*K-1] LS Exposure ratio between large droplet and short-range airborne [-] Lv Latent heat of vaporization [J*kg-1] md Droplet mass [kg] mI Mass of liquid in a droplet [kg] ms Mass of solid in a droplet [kg] M0 Jet initial momentum [m4*s-2] MW Molecular weight of H2O [kg*mol-1] MF Membrane fraction [-] n Number of droplets [n] n0 Number of droplets expelled immediately at mouth [n] Nin Number of droplets entering the inhalation zone [n] Nm Number of droplets potentially deposited on mucous membranes [n] Nt Total number of released droplets [n] Nu Nusselt number [-] p Total pressure [Pa] pv{infty} Vapour pressure distant from droplet surface [Pa] pvs Vapour pressure at droplet surface [Pa] Qjet Jet flow rate [m3*s-1] r Radial distance away from jet centreline [m] rd Droplet radius [m] R Radius of jet potential core [m] Rg Universal gas constant [J*K-1*mol-1] s Jet centreline trajectory length [m] Sin Width of region on sampler enclosed by limiting stream surface [m] Sh Sherwood number [-] Stc Stokes number in convergent part of air stream [-] Sth Stokes number for head [-] Stm Stokes number for mouth [-] t Time [s] T0 Initial temperature of jet [K] T{infty} Ambient temperature [K] Td Droplet temperature [K] u0 Initial velocity at mouth outlet [m*s-1] ud Droplet velocity [m*s-1] ug Gaussian velocity [m*s-1] ugas Gas velocity [m*s-1] ugc Gaussian centreline velocity [m*s-1] uin Inhalation velocity [m*s-1] ut Top-hat velocity [m*s-1] vp Individual droplet volume considering evaporation [m3] x Horizontal distance between source and target [m] z Jet vertical centreline position [m] {rho}0 Jet initial density [kg*m-3] {rho}{infty}Ambient air density [kg*m-3] {rho}d Droplet density [kg*m-3] {rho}g Gas density [kg*m-3] {Delta}{rho}Density difference between jet and ambient air [kg*m-3] g Gas dynamic viscosity [Pa*s] {varphi}Sampling ratio in axisymmetric flow system [-] c Impaction efficiency in convergent part of air stream [-]

The pharmacodynamics effect of propofol target-injection on different TCM physique types / 实用医学杂志

Objective Investigate the effect of EC50 of propofol target-injection in the different TCM (traditional Chinese medicine) physique types of patients who are in unconscious phase. Methods Depend on the standard protocol of TCM physique types sort and determination, we sorted 60 patients into three groups:Ping He (group A), Yang Xu (group B) and Yin Xu (group C), 20 patients per group. We applied the sequential experiment to measure the minimal EC50 and NI values of propofol when the patients were in the unconscious phase. Results The EC50 of propofol of group A, B and C are 3.85 μg/mL, 4.12 μg/mL and 3.43 μg/mL respectively. 95% confidence intervals of group A, B and C are 3.64 ~ 4.07 μg/mL, 3.92 ~ 4.33μg/mL and 3.26 ~ 3.60 μg/mL respectively. Conclusion There is a correlation between the different TCM physique types and the dosage of propofol target-injection.

Investigation of risk factors in the liver cancer of Wuwei city / 肿瘤研究与临床

Objective To investigate the widespread of the liver cancer risk factors in Wuwei city,where low-incidence for liver cancer and offer the cause clue to first-level prevention. Methods Investigate the risk factor and family history of the Wuwei city resident who wlth liver cancer by using case-control study.Estimate the liver cancer heredity mode with the method of Penrose and simple segregation analysis,calculate the degree of heritability with the metllod of Falconer,s regression.Detect the content of the resulting and promoting cancer fungi,volatility N-second nitroso compound in the meal,nitrate and nitrite in the drinking water and the vitamin C in the health adults'serum by means of culturing appraisement,experiment examination etc.Results The risk factom of liver cancer in the Wuwei city were history of viral 'hepatitis type B,kinsfolk tumor,the eating salting or mildewed foods,cirrhosis,drinking surface water,well water,or wine.By using segregation analysis and estimation of heredity mode show that the morbidity of liver cancer discrepancy to the monogenic inheritance mode,maybe the polygenic inheritance mode in Wuwei city.The h~2 of index case first degree relative was 58.74%.Picking out 8 kinds of nitrosamine,14 kinds of resulting and promoting cancer fungi from resident meal.The content of nitrate and nitrite was (38.97±3.14) mg/L,(0.086±0.043) mg/L respectively in shallow well water,the vitamin C in the health adults'serum in summer was(5.74±2.79)mg/L.Conclusion It can be seen that the history of viral hepatitis type B,kinsfolk tumor,eating salting or mildewed foods,cirrhosis,addicted to drink;higher content of nitrate and nitrite in the drinking water and strong carcinogens such as volatility N-nitroso compound in the meal,and also lackingprotection factors such as vitamin C are the risk factors of the Wuwei city resident who with liver cancer,Theinherit susceptivity is the internal environment of resulting cancer change.

Pigmented Villonodular Synovitis of the Knee Joint:Imaging Manifestations / 实用放射学杂志

Objective To explore the imaging characteristics of pigmented villonodular synovitis(PVNS) of knee joint.Methods X-ray,CT and MR imaging features of PVNS of knee confirmed by operation,arthroscope and pathology were retrospectively analysed with literatures review.Results X-ray could only show the swelling of the joint cpasules,the destruction,defect and sclerosis of the bone under the articular surface.CT could show the soft tissue nodules in joint cavity projected from joint capsule.MRI was sensitive in showing the thickened synovium of joint and joint effusion,the soft tissue nodules and thickened synovium of joint were iso-or low signal intensity on T1WI,isointensity in one and low or slight hyperintensity in 4 on T2WI.Multiple haemosiderin deposit nodules were seen in the thickened synovium,which were low signal intensity on T1WI and T2WI in 4 cases,and the nodules were enhanced obviously on contrast-enhanced MR images.Conclusion MRI possesses obviously in diagnosis of PVNS of knee joint than X-ray and CT,which is helpful in diagnosis and differential diagnosis of PVNS of knee joint.

Separation and identification of squalene in liver oil from Mustelus griseus / 中国海洋药物

The pure squalene(99.9%) was separated from liver oil of Mustelus griseus(Pietschmann) by TLC on silver nitrate-impregnated silica gel. The structure of squalene was confirmed by MS, ~1H-NMR and ~(13)C-NMR techniques.

THE SEPARATION OF HYDROCARBONS AND GLYCERIDES IN LIVER OIL OF MUSTELUS GRISEUS BY HPLC / 中国海洋药物

A new method of the separation of hydrocarbons and glycerides in liver oil of Mustelus jriseas was designed. The Waters Prep-500A Liquid Chromatograph with silica gel column and differential refractive index detector was used. The mobile phase was petroleum ether and ethyl acetate. The pure hydrocarbons' and glycerides were obtained from the liver oil.