| The global pandemic of coronavirus disease 2019（COVID-19）is a significant public health threat facing human society,causing enormous loss of life,health,and social and economic damage.Health care facilities where patients with COVID-19 are admitted are at greater risk of transmission due to their special functions and enclosed spaces.It is particularly critical to prevent and control infection in health care facilities.Aerosols are an important transmission route for the severe acute respiratory syndrome coronavirus 2（SARS-CoV-2）,and studying the transmission pattern of SARS-CoV-2aerosols in confined spaces and analyzing the impact of various factors on the risk of infection are important topics in current COVID-19 research.This paper studied the quantitative assessment of the risk of SARS-CoV-2 infection among health care workers in negative-pressure wards based on the diffusion and deposition pattern of SARS-CoV-2 aerosols in negative-pressure wards and respiratory tract.The main research content and results are as follows.1.The huoshenshan hospital negative-pressure ICU and the general negative-pressure wards were created as a 1:1 3D geometric models,including equipment,patients,and healthcare workers.The boundary parameters of air supply and exhaust and the boundary conditions of patient breathing in the negative-pressure ward were determined.CFD simulations of the flow field and aerosol diffusion deposition in the two negative-pressure wards were carried out.The results suggest that the flow field in the negative-pressure ward is the decisive factor in the migration pattern of aerosol particles.The equipment and facilities in the ward have an important influence on aerosol diffusion and deposition distribution.49%and 31%of aerosol particles are deposited on the surfaces of equipment and facilities in the negative-pressure ICU ward and the general negative-pressure ward,respectively.The aerosol deposition is more likely to occur on the surfaces of equipment and facilities than in other locations,and aerosol deposition is more likely to occur on the surfaces of equipment and facilities in the negative-pressure ICU and the general negative-pressure ward.The aerosol ventilation clearance rates in the negative-pressure ICU and general negative-pressure wards are 50%and 66%.In comparison,the proportion of aerosols suspended in the air of the two negative-pressure wards is 0.6%and 3%,respectively.2.A computational model of SARS-CoV-2 concentration distribution in the negative-pressure ward was developed using the Monte Carlo method.It has been revealed by comparing the simulation results of SARS-CoV-2 concentration distribution that agree well with the actual sampling values,indicating that the developed model could predict the SARS-CoV-2 concentration distribution in the negative-pressure ward more accurately.The calculated SARS-CoV-2 concentrations on the surface of objects and in the air in the negative-pressure ward suggest that the distribution of virus concentrations in the negative-pressure ward show relatively strong spatial heterogeneity.The virus concentrations on the surface of objects in the negative-pressure ICU ward ranged from103 to 104 Copies/m2,and the virus concentrations in the air in most areas ranged from9 to 15,500 Copies/m3.The virus concentration in the compartment is generally high.Virus concentration on the object’s surface in the general negative-pressure ward rang from 103 to 105 Copies/m2,the virus concentration in the air in most areas rang from 5to 50 Copies/m3,and the virus concentration on the surface of the objects rang from 103to 105Copies/m2.The transmission distance of SARS-CoV-2 aerosol in the negative-pressure ICU ward exceeds 10 m,more than twice the current detection value.3.Based on medical image segmentation reconstruction,bronchial tree growth algorithm,and idealized alveolar model,a multi-path complete respiratory geometry model of human airways with realistic respiratory tract characteristics and meeting the actual computational requirements was established.The airflow organization,aerosol deposition,and SARS-CoV-2 concentration distribution in human airways were computationally simulated.The results suggest that the flow field characteristics in different regions of the human respiratory tract are highly variable,with the nasal and laryngeal regions of the upper respiratory tract forming a more complex turbulent region.In contrast,the fine bronchi and alveoli flow are mainly laminar.The tracheobronchial regions have the highest aerosol deposition ratio in the respiratory tract,with the deposition ratio in the tracheobronchial being 59.6%under moderate activity intensity.The aerosol deposition ratios in the upper respiratory tract and alveoli regions are 11.3%and 29.1%.The distribution of SARS-CoV-2 concentration in the respiratory tract is consistent with the distribution of aerosols,with the highest virus concentration in the tracheobronchial at moderate activity intensity.The virus concentration in the tracheobronchial at the end of 3 hours in the bedside position of the negative-pressure ICU ward is 290.8 Copies for health care workers,and the virus concentration in the upper airway and alveoli is 64.9 Copies and 99.5 Copies respectively.4.A model was developed to quantitatively assess the risk of SARS-CoV-2 aerosol infection in health care workers in negative-pressure wards.The risk of infection in health care workers in negative-pressure wards was quantified in terms of two transmission routes:contact with contaminated surfaces and direct inhalation of aerosols.The effects of activity intensity,protection status,virus viability,and strain type on the risk of infection were quantified.The results show that the risk of surface contact infection in the general negative-pressure ward and the negative-pressure ICU is between 10-7 and 10-3,10-5 and 10-3 for unprotected moderate activity intensity,respectively,while the risk of inhalation infection is between 10-5 and 10-2 for both.The risk of inhalation infection during high-intensity activity is about twice that of moderate-intensity.The N95 mask has a significant protective effect,reducing the risk of inhalation infection by about 90%compared to unprotected wear.The viability of the virus affects the risk of infection,with the risk of infection for different materials on the same surface ranging from small to large due to differences in the half-life of SARS-CoV-2 on different surfaces:copper<cardboard<iron<plastic.Relative to the original,the risk of infection is significantly higher for Delta and Omicron than the lineage A/B,with the risk of infection by inhalation and contact in most areas of the negative-pressure ward being above 0.1 for Delta,above 0.5 for OmicronIn this paper,a model for calculating SARS-CoV-2 concentration distribution in negative pressure wards,which agrees well with actual detection values,was established,and the quantitative distribution of SARS-CoV-2 in the air and on the surface of objects in negative pressure wards was determined.This extends the existing CFD simulation study of SARS-CoV-2 aerosol concentration distribution to the quantitative calculation of virus concentration distribution.The distribution of inhaled SARS-CoV-2 in the respiratory tract was quantitatively calculated based on the multi-pathway whole-lung airway model.A quantitative assessment model for the risk of SARS-CoV-2 aerosol infection among medical staff in negative pressure wards was established.The impact of half-life,virus mutant,personal protective equipment,and activity intensity on infection risk was quantitatively analyzed. |
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