Occupancy-aided ventilation for airborne infection risk control:Continuously or intermittently reduced occupancies?

Ventilation is an important engineering measure to control the airborne infection risk of acute respiratory diseases,e.g.,Corona Virus Disease 2019(COVID-19).Occupancy-aided ventilation methods can effectively improve the airborne infection risk control performance with a sacrifice of decreasing working productivity because of the reduced occupancy.This study evaluates the effectiveness of two occupancy-aided ventilation methods,i.e.,the continuously reduced occupancy method and the intermittently reduced occupancy method.The continuously reduced occupancy method is determined by the steady equation of the mass conservation law of the indoor contaminant,and the intermittently reduced occupancy method is determined by a genetic algorithm-based optimization.A two-scenarios-based evaluation framework is developed,i.e.,one with targeted airborne infection risk control performance(indicated by the mean rebreathed fraction)and the other with targeted working productivity(indicated by the accumulated occupancy).The results show that the improvement in the airborne infection risk control performance linearly and quadratically increases with the reduction in the working productivity for the continuously reduced occupancy method and the intermittently reduced occupancy method respectively.At a given targeted airborne infection risk control performance,the intermittently reduced occupancy method outperforms the continuously reduced occupancy method by improving the working productivity by up to 92%.At a given targeted working productivity,the intermittently reduced occupancy method outperforms the continuously reduced occupancy method by improving the airborne infection risk control performance by up to 38%.

Nationwide evaluation of energy and indoor air quality predictive control and impact on infection risk for cooling season

Since the coronavirus disease 2019,the extended time indoors makes people more concerned about indoor air quality,while the increased ventilation in seeks of reducing infection probability has increased the energy usage from heating,ventilation,and air-conditioning systems.In this study,to represent the dynamics of indoor temperature and air quality,a coupled grey-box model is developed.The model is identified and validated using a data-driven approach and real-time measured data of a campus office.To manage building energy usage and indoor air quality,a model predictive control strategy is proposed and developed.The simulation study demonstrated 18.92%energy saving while maintaining good indoor air quality at the testing site.Two nationwide simulation studies assessed the overall energy saving potential and the impact on the infection probability of the proposed strategy in different climate zones.The results showed 20%–40%energy saving in general while maintaining a predetermined indoor air quality setpoint.Although the infection risk is increased due to the reduced ventilation rate,it is still less than the suggested threshold(2%)in general.

Quantification of how mechanical ventilation influences the airborne infection risk of COVID-19 and HVAC energy consumption in office buildings

This paper presents an EnergyPlus-based parametric analysis to investigate the infection risk of Coronavirus Disease 2019(COVID-19)under different mechanical ventilation scenarios for a typical medium-sized office building in various climate zones.A Wells-Riley(WR)based Gammaitoni-Nucci(GN)model was employed to quantitatively calculate the airborne infection risk.The selected parameters for the parametric analysis include the climate zone,outdoor air fraction,fraction of infectors,quanta generation rate,and exposure time.The loss and deposition of particles are not considered.The results suggest that the COVID-19 infection risk varies significantly with climate and season under different outdoor air fraction scenarios since the building heating and cooling load fundamentally impacts the supply airflow rate and thus directly influences the amount of mechanical ventilation,which determines the dilution ratio of contaminants.This risk assessment identified the climate zones that benefit the most and the least from increasing the outdoor air fraction.The climate zones such as 1A(Honolulu,HI),2B(Tucson,AZ),3A(Atlanta,GA),and 7(International Falls,MN)are the most energy-efficient locations when it comes to increasing the outdoor air fraction to reduce the COVID-19 infection risk.In contrast,the climate zones such as 6A(Rochester,MN)and 6B(Great Falls,MT)are the least energy-efficient ones.This paper facilitates understanding a widely recommended COVID-19 risk mitigation strategy(i.e.,increase the outdoor airflow rate)from the perspective of energy consumption.

Possible high COVID-19 airborne infection risk in deep and poorly ventilated 2D street canyons

Despite the widespread assumption that outdoor environments provide sufficient ventilation and dilution capacity to mitigate the risk of COVID-19 infection,there is little understanding of airborne infection risk in outdoor urban areas with poor ventilation.To address this gap,we propose a modified Wells-Riley model based on the purging flow rate(QPFR),by using computational fluid dynamics(CFD)simulations.The model quantifies the outdoor risk in 2D street canyons with different approaching wind speeds,urban heating patterns and aspect ratios(building height to street width).We show that urban morphology plays a critical role in controlling airborne infectious disease transmission in outdoor environments,especially under calm winds;with deep street canyons(aspect ratio>3)having a similar infection risk as typical indoor environments.While ground and leeward wall heating could reduce the risk,windward heating(e.g.,windward wall~10 K warmer than the ambient air)can increase the infection risk by up to 75%.Our research highlights the importance of considering outdoor infection risk and the critical role of urban morphology in mitigating airborne infection risk.By identifying and addressing these risks,we can inform measures that may enhance public health and safety,particularly in densely populated urban environments.

Risk factors and strategy for surgical incision infection in department of abdominal surgery

Objective To study the risk factors of surgical wound infection among the patients in department of abodominal surgery. Methods The factors on surgical wound infection were investigated by retrospective study. The diagnosis standard was based on Diagnosis Standard of Hospital Infection published by Ministry of Health.

Treatment Options for Pin Site Infection during Kirschner Wires in Elective Forefoot Surgery

The Kirschner wires (K-wires) are stiff and straight wires made of smooth stainless steel. These are used in surgery to aid in repairing the process of a fractured bone. In forefoot elective surgeries, these pins are mostly used for fixation of the phalangeal or metatarsal area. These wires are usually either buried or exposed, The exposed wires do not require another operation to remove them and are generally preferred. In using the forefoot surgery history of a single surgeon which was taken for 3 years. The purpose of this study is to evaluate the occurrence of infections following elective surgeries of the forefoot that were fixed using k-pins and to indicate an effective treatment option for resolving the infection. The inclusion criteria set for this study was to remove any patient having any disease except for diabetes. Moreover, the age limit was set to be 18 - 44, making a final sample of 50 people, prescribed prophylactic antibiotics or early removal of k-pins, where necessary. The researcher recorded demographic and biological data from the patients such as age, BMI, and smoking status were recorded. The researcher conducted a Univariate analysis via a Chi-square test. 50 Patients (82 K-wires) were analyzed. Results showed that surgery type, BMI, and smoking were three variables that affect the infection growth significantly while diabetes and type of cleaning disinfectant had marginal effects. Further study is required to clarify the best treatments in this area, as the treatment option antibiotics have nearly similar results.

Risk factors of infected pancreatic necrosis secondary to severe acute pancreatitis

BACKGROUND： Severe acute pancreatitis（SAP） remains a clinical challenge with considerable morbidity and mortality.An early identification of infected pancreatic necrosis（IPN）, a life-threatening evolution secondary to SAP, is obliged for a more preferable prognosis. Thus, the present study was conducted to identify the risk factors of IPN secondary to SAP. METHODS： The clinical data of patients with SAP were retrospectively analyzed. Univariate and multivariate logistic regression analyses were sequentially performed to assess the associations between the variables and the development of IPN secondary to SAP. A receiver operating characteristic（ROC） curve was created for each of the qualified independent risk factors. RESULTS： Of the 115 eligible patients, 39（33.9%） progressed to IPN, and the overall in-hospital mortality was 11.3%（13/115）.The early enteral nutrition（EEN）（P=0.0092, OR=0.264）, maximum intra-abdominal pressure（IAP）（P=0.0398, OR=1.131）and maximum D-dimer level（P=0.0001, OR=1.006） in the first three consecutive days were independent risk factors associated with IPN secondary to SAP. The area under ROC curve（AUC） was 0.774 for the maximum D-dimer level in the first three consecutive days and the sensitivity was 90% and the specificity was 58% at a cut-off value of 933.5 μg/L; the AUC was 0.831 for the maximum IAP in the first three consecutive days and the sensitivity was 95% and specificity was 58%at a cut-off value of 13.5 mm Hg. CONCLUSIONS： The present study suggested that the maximum D-dimer level and/or maximum IAP in the first three consecutive days after admission were risk factors of IPN secondary to SAP; an EEN might be helpful to prevent the progression of IPN secondary to SAP.

Bloodstream Infections Caused by Enterococcus spp：A 10-year Retrospective Analysis at a Tertiary Hospital in China

In order to discover the risk factors for 30-day mortality in bloodstream infections（BSI） caused by Enterococcus spp.strains,we explored the clinical and therapeutic profile of patients with Enterococcus spp.BSI and the characteristics of this condition.A total of 64 patients with BSI caused by Enterococcus spp.who were treated in our hospital between 2006 and 2015 were included in the study.The clinical features of patients,microbiology,and 30-day mortality were collected from the electronic medical records database and analyzed.The results showed that there were 38 patients infected by Enterococcus faecalis（E.faecalis）,24 by Enterococcus faecium（E.faecium）,1 by Enterococcus casseliflavus（E.casseliflavus）,and 1 by Enterococcus gallinarum（E.gallinarum）.A Charlson comorbidity score ≥5,corticosteroid treatment,placement of catheters or other prosthetic devices and history of antibiotic use were found more frequently in E.faecium BSI patients than in E.faecalis patients（P=0.017,P=0.027,P=0.008 and P=0.027,respectively）.Furthermore,the univariate and multivariate analysis showed that corticosteroid treatment（OR=17.385,P=0.008）,hospital acquisition（OR=16.328,P=0.038）,and vascular catheter infection（OR=14.788,P=0.025） were all independently associated with 30-day mortality.Our results indicate that E.faecalis and E.faecium are two different pathogens with unique microbiologic characteristics,which cause different clinical features in BSI,and the empiric antimicrobial treatments are paramount for patients with enterococcal BSI.

AWells-Riley/based COVID-19 infectiousrisk assessment model combining both short rangeandroom scale effects

There is growing evidence of the high transmission potential of COVID-19 through virus-laden aerosols.Because aerosols are inhaled in various concentrations,an overall assessment of transmission risks at different indoor scales is crucial.However,a comprehensive risk assessment method that evaluates the direct link between short-range and room-scale zones is stl lacking.In this paper,a risk assessment model combining both short-range and room-scale effects is developed to obtain effective reproduction number in confined indoor environments,called Turbulent Jet Wells Riley(TJWR)model.Combined with the viral load data and aerosol generation data of different human respiratory activities,the Monte Carlo simulation method is applied to calculate the quanta emission rate,which further provides the input parameters of the TJWR model.Three known outbreaks(Hangzhou banquet hall X,Guangzhou restaurant Y,and Hong Kong restaurant Z,China)are chosen to validate the TJWR model.Results show that the TJWR model is more efficient than the original Wells-Riley model.The average relative error of the TJWR model ranges between 9%and 44%,while for the Wells-Riley model,it ranges between 57%and 78%.The TJWR model also proves that infection risk assessments using the well-mixed assumption can systematically underestimate the transmission risk for those close to the source.Additionally,there is a significant positive linear correlation between the total number of exposed individuals at the short-range and the effective reproduction number.This newly developed TJWR model has great potential for rapid and real-time overall airborne transmission risk assessment in buildings and cities.

Viruses and autism: A Bi-mutual cause and effect

Autism spectrum disorder(ASD)is a group of heterogeneous,multi-factorial,neurodevelopmental disorders resulting from genetic and environmental factors interplay.Infection is a significant trigger of autism,especially during the critical developmental period.There is a strong interplay between the viral infection as a trigger and a result of ASD.We aim to highlight the mutual relationship between autism and viruses.We performed a thorough literature review and included 158 research in this review.Most of the literature agreed on the possible effects of the viral infection during the critical period of development on the risk of developing autism,especially for specific viral infections such as Rubella,Cytomegalovirus,Herpes Simplex virus,Varicella Zoster Virus,Influenza virus,Zika virus,and severe acute respiratory syndrome coronavirus 2.Viral infection directly infects the brain,triggers immune activation,induces epigenetic changes,and raises the risks of having a child with autism.At the same time,there is some evidence of increased risk of infection,including viral infections in children with autism,due to lots of factors.There is an increased risk of developing autism with a specific viral infection during the early developmental period and an increased risk of viral infections in children with autism.In addition,children with autism are at increased risk of infection,including viruses.Every effort should be made to prevent maternal and early-life infections and reduce the risk of autism.Immune modulation of children with autism should be considered to reduce the risk of infection.

Numerical Study of Airborne Droplets Propagation Inside a Hospital Consulting Room

The outbreak of Corona Virus(COVID-19)has spread over a large number of countries.The virus is typically transported inside liquid droplets produced by human beings.As a result,doctors operating in the consulting rooms of hospitals are potentially exposed to high risk.Taking into account the evaporation of droplets and using a hybrid Eulerian-Lagrangian framework to determine the airflow pattern and corresponding motion of droplets,in the present study,the motion of droplets is investigated with regard to the situation in which doctors check patients in front of their bed.A turbulence model(RNG k-ɛ)is used.The purification capacity of different ventilation systems is compared.The risk of cross-infection between doctors and patients is also evaluated.

Impact of ionizers on prevention of airborne infection in classroom

Infectious diseases(e.g.,coronavirus disease 2019)dramatically impact human life,economy and social development.Exploring the low-cost and energy-saving approaches is essential in removing infectious virus particles from indoors,such as in classrooms.The application of air purification devices,such as negative ion generators(ionizers),gains popularity because of the favorable removal capacity for particles and the low operation cost.However,small and portable ionizers have potential disadvantages in the removal efficiency owing to the limited horizontal diffusion of negative ions.This study aims to investigate the layout strategy(number and location)of ionizers based on the energy-efficient natural ventilation in the classroom to improve removal efficiency(negative ions to particles)and decrease infection risk.Three infected students were considered in the classroom.The simulations of negative ion and particle concentrations were performed and validated by the experiment.Results showed that as the number of ionizers was 4 and 5,the removal performance was largely improved by combining ionizer with natural ventilation.Compared with the scenario without an ionizer,the scenario with 5 ionizers largely increased the average removal efficiency from around 20%to 85%and decreased the average infection risk by 23%.The setup with 5 ionizers placed upstream of the classroom was determined as the optimal layout strategy,particularly when the location and number of the infected students were unknown.This work can provide a guideline for applying ionizers to public buildings when natural ventilation is used.

Temporal-spatial risk assessment of COVID-19 under the influence of urban spatial environmental parameters:The case of Shenyang city

Respiratory infection is the main route for the transmission of coronavirus pneumonia,and the results have shown that the urban spatial environment significantly influences the risk of infection.Based on the Wells-Riley model of respiratory infection probability,the study determined the human respiratory-related parameters and the effective influence range;extracted urban morphological parameters,assessed the ventilation effects of different spatial environments,and,combined with population flow monitoring data,constructed a method for assessing the risk of Covid-19 respiratory infection in urban-scale grid cells.In the empirical study in Shenyang city,a severe cold region,urban morphological parameters,population size,background wind speed,and individual behavior patterns were used to calculate the distribution characteristics of temporal and spatial concomitant risks in urban areas grids under different scenarios.The results showed that the correlation between the risk of respiratory infection in urban public spaces and the above variables was significant.The exposure time had the greatest degree of influence on the probability of respiratory infection risk among the variables.At the same time,the change in human body spacing beyond 1 m had a minor influence on the risk of infection.Among the urban morphological parameters,building height had the highest correlation with the risk of infection,while building density had the lowest correlation.The actual point distribution of the epidemic in Shenyang from March to April 2022 was used to verify the evaluation results.The overlap rate between medium or higher risk areas and actual cases was 78.55%.The planning strategies for epidemic prevention and control were proposed for the spatial differentiation characteristics of different risk elements.The research results can accurately classify the risk level of urban space and provide a scientific basis for the planning response of epidemic prevention and control and the safety of public activities.

COVID-19 transmission and control in land public transport:A literature review

Land public transport is an important link within and between cities,and how to control the transmission of COVID-19 in land public transport is a critical issue in our daily lives.However,there are still many inconsistent opinions and views about the spread of SARS-CoV-2 in land public transport,which limits our ability to implement effective interventions.The purpose of this review is to overview the literature on transmission characteristics and routes of the epidemic in land public transport,as well as to investigate factors affecting its spread and provide feasible measures to mitigate the infection risk of passengers.We obtained 898 papers by searching the Web of Science,Pubmed,and WHO global COVID database by keywords,and finally selected 45 papers that can address the purpose of this review.Land public transport is a high outbreak area for COVID-19 due to characteristics like crowding,inadequate ventilation,long exposure time,and environmental closure.Different from surface touch transmission and drop spray transmission,aerosol inhalation transmission can occur not only in short distances but also in long distances.Insufficient ventilation is the most important factor influencing long-distance aerosol transmission.Other transmission factors(e.g.,interpersonal distance,relative orientation,and ambient conditions)should be noticed as well,which have been summarized in this paper.To address various influencing factors,it is essential to suggest practical and efficient preventive measures.Among these,increased ventilation,particularly the fresh air(i.e.,natural ventilation),has proven to effectively reduce indoor infection risk.Many preventive measures are also effective,such as enlarging social distance,avoiding face-to-face orientation,setting up physical partitions,disinfection,avoiding talking,and so on.As research on the epidemic has intensified,people have broken down many perceived barriers,but more comprehensive studies on monitoring systems and prevention measures in land public transport are still needed.

Effectiveness of air cleaner on mitigating the transmission of respiratory disease in a dental clinic environment

In dental clinics with an open floor plan,the risk of patient-to-patient transmission of respiratory disease is a concern.During dental procedures large amounts of bioaerosol are produced and patients cannot wear personal protective equipment.This paper examines how to effectively deploy air cleaner to reduce the infection risk in dental clinics with an open floor plan.Various locations of air cleaners at various clean air delivery rates(CADRs)were investigated.The dispersion of bioaerosol was studied through numerical simulations,and risk assessment was performed by a dose-response method.The findings indicated that dental patients downstream of the background ventilation have a higher infection risk than those to the left and right of an infected patient(i.e.,the source).The lowest infection risks for the adjacent patients were found when the air cleaner was place opposite to the dentists,i.e.,on the floor at low CADR levels of 2.2 m^(3)/min or on the bench at CADR levels of 4.4 m^(3)/min or greater.The results of this study indicated that air cleaner can mitigate the risk of patient-to-patient transmission of SARS-CoV-2 in dental clinics with an open floor plan.Background CADR levels determine the optimal placement of air cleaners.

Assessing impact of intermittent window opening strategies on pathogen-laden droplet dispersion in a coach bus

Opening windows in coach buses is a practical approach to improving natural ventilation and mitigating infection risk(IR).Due to human behavior and weather conditions,the intermittent window opening strategy(IWOS)is a more common practice than keeping windows constantly open.Despite its prevalence,there are no studies exploring IWOS specifically in vehicles.We employed indoor-outdoor coupled CFD simulations to assess the effects of various IWOS on pathogen-laden droplet(PLD)dispersion and IR in a coach bus that occurred a COVID-19 outbreak in Hunan,China.Results reveal that after ventilating through two skylights for 600–1800 s,opening front and rear windows(FW+RW)or FW with a wind catcher(FW+WCH)for just 40 s can reduce PLD concentration(Cave)to 5%of its initial level and the intake fraction of the infector’s neighbor(IFn)drops by 95%.Upon closing FW+RW or FW+WCH,Cave and IFn take over 580 s to return to the pre-opening level.Moreover,intermittent FW opening halves Cave and IFn within 7 min,but leads to rapid increases upon window closure.Therefore,opening FW+RW and FW+WCH intermittently have pronounced impacts on indoor PLD concentration and are applicable approaches to control respiratory disease transmission in vehicles.According to the inhaled viral dose,it is recommended to open windows when driving time is over 12 minutes to reduce infection risk.In scenarios like epidemiological surveys and risk assessments,where assessing passenger infection risk is vital,some behaviors of opening windows cannot be overlooked and necessitate extra attention.

A signature for biological heterogeneity in susceptibility to HIV infection?

Data on female sex workers and sero-discordant couples indicate a pattern of waning of the risk of HIV infection with longer duration of exposure to infected partners.Understanding risk of HIV acquisition and transmission is critical to understanding HIV epidemiology and informing prevention interventions.Informed by empirical data,we aimed to develop a statistical model to explain these observations.In our proposed model,the time to infection for each individual is exponentially distributed,but the marginal(population averaged)distribution of time to infection follows a Weibull distribution with shape parameter of about 0.5,and with the L
evy distribution being the mixing distribution.Simulations based on this model demonstrated how HIV epidemics are destined to emerge rapidly,because of the rapid sero-conversion upon exposure,but also simultaneously destined to saturate and decline rapidly after emergence,just as observed for the HIV epidemics in sub-Saharan Africa.These results imply considerable individual variability in infection risk,probably because of biological heterogeneity in the susceptibility to HIV infection.Factoring this variability in mathematical models,through the methodology provided here,could be critical for valid estimations of impact of HIV interventions and assessments of cost-effectiveness.

Senescent remodeling of the immune system and its contribution to the predisposition of the elderly to infections

Objective To review the senescent remodeling of the immune system with aging and its relevance to the increased susceptibility of the elderly to infectious diseases, along with an outlook on emerging immunological biomarkers. Data sources The data selected were from PubMed with relevant published articles in English or French from 1995 to the present. Searches were made using the terms immunosenescence and aging paired with the following： innate immunity, T-celr, B-cell, adaptive immunity and biomarkers. Articles were reviewed for additional citations and some information was gathered from web searches. Study selection Articles on aging of both the innate and adaptive immunity were reviewed, with special attention to the remodeling effect on the ability of the immune system to fight infectious diseases. Articles related to biomarkers of immunosenescence were selected with the goal of identifying immunological biomarkers predisposing the elderly to infections. Results Innate immunity is generally thought to be relatively well preserved or enhanced during aging compared with adaptive immunity which manifests more profound alterations. However, evidence, particularly in the last decade, reveals that both limbs of the immune system undergo profound remodeling with aging. Reported data on adaptive immunity is consistent and changes are well established but conflicting results about innate immunity were reported between in vivo and in vitro studies, as well as between murine and human studies. Epidemiological data suggests increased predisposition of the elderly to infections, but no compelling scientific evidence has directly linked senescent immune remodeling to this increased susceptibility. Recently, growing interest in identifying immunological biomarkers and defining immune risk phenotypes/profiles （IRP） has been expressed. Identification of biomarkers is in its early days and few potential biomarkers have been identified, with the Swedish having defined one IRP based on the adaptive immune response. Conclusions Aging does not necessarily lead to an unavoidable decline in immune functions. Instead, a complex remodeling occurs. Despite the lack of compelling scientific evidence, senescent immune remodeling surely is a significant contributing factor to the increased risk and severity of infections in the elderly. Although, no immunological biomarker has been formally linked to the increased risk of infections in the elderly, biomarkers remain a promising tool to predict the likelihood of healthy aging, the level of immune competence, and mortality risk in the elderly. Hence, more research is required to define healthy aging and identify immunological biomarkers.

Airborne transmission of virus-laden droplets in an aircraft cabin

This study investigates the airborne transmission of virus-laden droplets generated by a cough of patients in an aircraft cabin to reveal the infection risk of taking an airplane.The influence of the ventilation system on the flow feld of the cabin was analysed to reveal its effects on the airbore transmission ofvirus-laden droplets.Meanwhile.human body heat was also considered in the simulations.The results show that hot plume due to human body hent has a significant impact on the upward movement of virus-laden droplets.The virus-laden droplets expelled by a cough can be transmitted to the region two to three rows away from the generator.Particularly,the transverse motion present in the early stage of the droplet transmission results in a high infection risk to the passengers in the same row as the patient.This work gives insight into the understanding of the airborne transmission of virus-laden droplets in the entire passenger cabin.