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

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 [-]

Experiences in construction of infection disease outpatient service / 中华临床感染病杂志

The infectious disease outpatient service as a frontier is an important fulcrum of public health service. Its standardized construction is an important support for ensuring medical safety, reducing nosocomial infections, and controlling the epidemic of infectious diseases. The sub-specialty outpatient service of infection diseases includes fever outpatient service, intestinal outpatient service, tuberculosis outpatient service, AIDS outpatient service, liver disease outpatient service, etc. According to the characteristics of each subspecialty outpatient service and combining with clinical practice, we elaborated the setting norms of subspecialty outpatient service for common infectious diseases from the perspective of planning and design, building layout, equipment and facilities configuration, staffing, daily management and demonstration.