Role of ventilation in airborne transmission of infectious agents in the built environment - a multidisciplinary systematic review

Evaluating the commercial airliner cabin environment with different air distribution systems

Ventilation systems for commercial airliner cabins are important in reducing contaminant transport and maintaining thermal comfort. To evaluate the performance of a personalized displacement ventilation system, a conventional displacement ventilation system, and a mixing ventilation system, this study first used the Wells-Riley equation integrated with CFD to obtain the SARS quanta value based on a specific SARS outbreak on a flight. This investigation then compared the three ventilation systems in a seven-row section of a fully occupied, economy-class cabin in Boeing 737 and Boeing 767 airplanes. The SARS quanta generation rate obtained for the index patient could be used in future studies. For all the assumed source locations, the passengers' infection risk by air in the two planes was the highest with the mixing ventilation system, while the conventional displacement ventilation system produced the lowest risk. The personalized ventilation system performed the best in maintaining cabin thermal comfort and can also reduce the infection risk. This system is recommended for airplane cabins.

A Multicompartment SIS Stochastic Model with Zonal Ventilation for the Spread of Nosocomial Infections: Detection, Outbreak Management, and Infection Control

In this work, we study the environmental and operational factors that influence airborne transmission of nosocomial infections. We link a deterministic zonal ventilation model for the airborne distribution of infectious material in a hospital ward, with a Markovian multicompartment SIS model for the infection of individuals within this ward, in order to conduct a parametric study on ventilation rates and their effect on the epidemic dynamics. Our stochastic model includes arrival and discharge of patients, as well as the detection of the outbreak by screening events or due to symptoms being shown by infective patients. For each ventilation setting, we measure the infectious potential of a nosocomial outbreak in the hospital ward by means of a summary statistic: the number of infections occurred within the hospital ward until end or declaration of the outbreak. We analytically compute the distribution of this summary statistic, and carry out local and global sensitivity analysis in order to identify the particular characteristics of each ventilation regime with the largest impact on the epidemic spread. Our results show that ward ventilation can have a significant impact on the infection spread, especially under slow detection scenarios or in overoccupied wards, and that decreasing the infection risk for the whole hospital ward might increase the risk in specific areas of the health-care facility. Moreover, the location of the initial infective individual and the protocol in place for outbreak declaration both form an interplay with ventilation of the ward.

Indoor hospital air and the impact of ventilation on bioaerosols: a systematic review

Healthcare-acquired infections (HAIs) continue to persist in hospitals, despite the use of increasingly strict infection-control precautions. Opportunistic airborne transmission of potentially pathogenic bioaerosols may be one possible reason for this persistence. Therefore, this study aimed to systematically review the concentrations and compositions of indoor bioaerosols in different areas within hospitals and the effects of different ventilation systems. Electronic databases (Medline and Web of Science) were searched to identify articles of interest. The search was restricted to articles published from 2000 to 2017 in English. Aggregate data was used to examine the differences in mean colony forming units per cubic metre (cfu/m³) between different hospital areas and ventilation types. A total of 36 journal articles met the eligibility criteria. The mean total bioaerosol concentrations in the different areas of the hospitals were highest in the inpatient facilities (77 cfu/m³, 95% confidence interval (CI): 55-108) compared with the restricted (13cfu/m³, 95% CI: 10-15) and public areas (14 cfu/m³, 95% CI: 10-19). Hospital areas with natural ventilation had the highest total bioaerosol concentrations (201 cfu/m³, 95% CI: 135-300) compared with areas using conventional mechanical ventilation systems (20 cfu/m³, 95% CI: 16-24). Hospital areas using sophisticated mechanical ventilation systems (such as increased air changes per hour, directional flow and filtration systems) had the lowest total bioaerosol concentrations (9 cfu/m³, 95% CI: 7-13). Operating sophisticated mechanical ventilation systems in hospitals contributes to improved indoor air quality within hospitals, which assists in reducing the risk of airborne transmission of HAIs.

On the interpretation of bioaerosol exposure measurements and impacts on health

Bioaerosols are recognized as one of the main transmission routes for infectious diseases and are responsible for other various types of health effects through inhalation and potential ingestion. Associating exposure with bioaerosol and health problems is challenging, and adequate exposure monitoring is a top priority for aerosol scientists. The multiple factors affecting bioaerosol content, the variability in the focus of each bioaerosol exposure study, and the variations in experimental design and the standardization of methods make bioaerosol exposure studies very difficult. Therefore, the health impacts of bioaerosol exposure are still poorly understood. This paper presents a brief description of a state-of-the-art development in bioaerosol exposure studies supported by studies on several related subjects. The main objective of this paper is to propose new considerations for bioaerosol exposure guidelines and the development of tools and study designs to better interpret bioaerosol data. The principal observations and findings are the discrepancy of the applicable methods in bioaerosol studies that makes result comparison impossible. Furthermore, the silo mentality helps in creating a bigger gap in the knowledge accumulated about bioaerosol exposure. Innovative and original ideas are presented for aerosol scientists and health scientists to consider and discuss. Although many examples cited herein are from occupational exposure, the discussion has relevance to any human environment. This work gives concrete suggestions for how to design a full bioaerosol study that includes all of the key elements necessary to help understand the real impacts of bioaerosol exposure in the short term. The creation of the proposed bioaerosol public database could give crucial information to control the public health. Implications: How can we move toward a bioaerosol exposure guidelines? The creation of the bioaerosol public database will help accumulate information for long-term association studies and help determine specific exposure biomarkers to bioaerosols. The implementation of such work will lead to a deeper understanding and more efficient utilization of bioaerosol studies to prevent public health hazards.

Biological Particles in the Indoor Environment

Airborne microorganisms are very difficult to assess accurately under field conditions owing to differences in the sample collection efficiency of the selected sampler and variations in DNA extraction efficiencies. Consequently, bioaerosol abundance and biodiversity can be underestimated, making it more difficult to link specific bioaerosol components to diseases and human health risk. Owing to the low biomass in air samples, it remains a challenge to obtain a representative microbiological sample to recover sufficient DNA for downstream analyses. Improved sampling methods are particularly crucial, especially for investigating viral communities, owing to the extremely low biomass of viral particles in the air compared with other environments. Without detailed information about sampling, characterization and enumeration techniques, interpretation of exposure level is very difficult. Despite this, bioaerosol research has been enhanced by molecular tools, especially next-generation sequencing approaches that have allowed faster and more detailed characterization of air samples.

Cost-Effectiveness of Multifaceted Built Environment Interventions for Reducing Transmission of Pathogenic Bacteria in Healthcare Facilities

OBJECTIVES

The objective of this study is to determine the optimal allocation of budgets for pairs of alterations that reduce pathogenic bacterial transmission. Three alterations of the built environment are examined: handwashing stations (HW), relative humidity control (RH), and negatively pressured treatment rooms (NP). These interventions were evaluated to minimize total cost of healthcare-associated infections (HAIs), including medical and litigation costs.

BACKGROUND

HAIs are largely preventable but are difficult to control because of their multiple mechanisms of transmission. Moreover, the costs of HAIs and resulting mortality are increasing with the latest estimates at US$9.8 billion annually.

METHOD

Using 6 years of longitudinal multidrug-resistant infection data, we simulated the transmission of pathogenic bacteria and the infection control efforts of the three alterations using Chamchod and Ruan's model. We determined the optimal budget allocations among the alterations by representing them under Karush-Kuhn-Tucker conditions for this nonlinear optimization problem.

RESULTS

We examined 24 scenarios using three virulence levels across three facility sizes with varying budget levels. We found that in general, most of the budget is allocated to the NP or RH alterations in each intervention. At lower budgets, however, it was necessary to use the lower cost alterations, HW or RH.

CONCLUSIONS

Mathematical optimization offers healthcare enterprise executives and engineers a tool to assist with the design of safer healthcare facilities within a fiscally constrained environment. Herein, models were developed for the optimal allocation of funds between HW, RH, and negatively pressured treatment rooms (NP) to best reduce HAIs. Specific strategies vary by facility size and virulence.

Bioaerosols Play a Major Role in the Nasopharyngeal Microbiota Content in Agricultural Environment

Background: Bioaerosols are a major concern for public health and sampling for exposure assessment purposes is challenging. The nasopharyngeal region could be a potent carrier of long-term bioaerosol exposure agents. This study aimed to evaluate the correlation between nasopharyngeal bacterial flora of swine workers and the swine barns bioaerosol biodiversity. Methods: Air samples from eight swine barns as well as nasopharyngeal swabs from pig workers (n = 25) and from a non-exposed control group (n = 29) were sequenced using 16S rRNA gene high-throughput sequencing. Wastewater treatment plants were used as the industrial, low-dust, non-agricultural environment control to validate the microbial link between the bioaerosol content (air) and the nasopharynxes of workers. Results: A multivariate analysis showed air samples and nasopharyngeal flora of pig workers cluster together, compared to the non-exposed control group. The significance was confirmed with the PERMANOVA statistical test (p-value of 0.0001). Unlike the farm environment, nasopharynx samples from wastewater workers did not cluster with air samples from wastewater treatment plants. The difference in the microbial community of nasopharynx of swine workers and a control group suggest that swine workers are carriers of germs found in bioaerosols. Conclusion: Nasopharynx sampling and microbiota could be used as a proxy of air sampling for exposure assessment studies or for the determination of exposure markers in highly contaminated agricultural environments.

A systematic scoping review of environmental health conditions and hygiene behaviors in homeless shelters

BACKGROUND

There are well-established relationships between health and homelessness, and shelters can facilitate the transmission of diseases and contribute to their prevention. Adequate environmental health conditions and hygiene behaviors in homeless shelters are fundamental to the health of their clients, a marginalized population. We report the status of environmental health conditions and hygiene behaviors in homeless shelters and associated health outcomes; interventions to improve these conditions, behaviors, and outcomes; and obstacles to improvement.

METHODS

PubMed, Web of Science, Scopus, and EBSCOhost were searched for peer-reviewed studies, and additional sources for grey literature. Studies were included if they reported primary data on one or more environmental health condition or hygiene behavior in homeless shelters.

RESULTS

Twenty-eight studies were included in the review. Insufficient ventilation systems, unhygienic bedding, and overcrowding were the most documented environmental health and hygiene deficiencies in homeless shelters, and tuberculosis infections and skin diseases were the most documented associated health outcomes among clients. Studies frequently recommended or described implementation of behavioral and administrative controls, ventilation system improvements, and ultraviolet germicidal irradiation fixtures.

DISCUSSION

Most studies addressed airborne transmission of tuberculosis and were conducted in high-income countries, revealing an imbalance in the literature. Insufficient resources and the transience of clients are barriers to improving hygiene behaviors and environmental conditions in homeless shelters. Further investment and research into ensuring adequate hygiene and environmental health in this setting can protect and promote the health and well-being of people experiencing homelessness.

Evaluation of HVAC Design Parameters in High-Performance Hospital Operating Theatres

Unidirectional flow air-conditioning systems are suitable for achieving indoor air quality required in high-performance operating rooms (organ transplants, cardiac surgery, aorta, orthopedic, burns, etc.). This paper analyzes indoor environmental conditions and technical and hygienic requirements for the design of heating, ventilation, and air-Conditioning (HVAC) systems for high-performance operating theatres. The main standards applicable to this type of operating rooms were compiled. Standard UNE 100713:2015, ASHRAE Standard 170-2017, and the European pre-norm EN 16244 were analyzed. A case study shows the lack of uniformity in design criteria and their ranges of values, which generates different design approaches. It was concluded that using these standards applicable to high-performance operating rooms leads to very different indoor environmental conditions for patients and medical personnel—air velocity profiles, air movement pattern, temperature, relative humidity gradients, and pressure stratification. Computational fluid dynamics (CFD) studies have been shown to detect areas of haven that favor microbiological load accumulation. In this way, it is possible to define cleaning protocols to attend these anomalies in a preventive way.

Coupling Computational Fluid Dynamics Simulations and Statistical Moments for Designing Healthy Indoor Spaces

Cross-contamination between occupants in an indoor space may occur due to transfer of infectious aerosols. Computational fluid dynamics (CFD) provides detailed insight into particle transport in indoor spaces. However, such simulations are site-specific. This study couples CFD with statistical moments and establishes a framework that transitions site-specific results to generating guidelines for designing "healthy" indoor spaces. Eighteen cases were simulated, and three parameters were assessed: inlet/outlet location, air changes per hour, and the presence/absence of desks. Aerosol release due to a simulated "sneeze" in a two-dimensional ventilated space was applied as a test case. Mean, standard deviation, and skewness of the velocity profiles and particle locations gave an overall picture of the spread and movement of the air flow in the domain. A parameter or configuration did not dominate the values, confirming the significance of considering the combined influence of multiple parameters for determining localized air-flow characteristics. Particle clustering occurred more when the inlet was positioned above the outlet. The particle dispersion pattern could be classified into two time zones: "near time", <60 s, and "far time", >120 s. Based on dosage, the 18 cases were classified into three groups ranging from worst case scenario to best case scenario.

Effects of indoor environmental parameters related to building heating, ventilation, and air conditioning systems on patients' medical outcomes: A review of scientific research on hospital buildings

The indoor environment of a mechanically ventilated hospital building controls infection rates as well as influences patients' healing processes and overall medical outcomes. This review covers the scientific research that has assessed patients' medical outcomes concerning at least one indoor environmental parameter related to building heating, ventilation, and air conditioning (HVAC) systems, such as indoor air temperature, relative humidity, and indoor air ventilation parameters. Research related to the naturally ventilated hospital buildings was outside the scope of this review article. After 1998, a total of 899 papers were identified that fit the inclusion criteria of this study. Of these, 176 papers have been included in this review to understand the relationship between the health outcomes of a patient and the indoor environment of a mechanically ventilated hospital building. The purpose of this literature review was to summarize how indoor environmental parameters related to mechanical ventilation systems of a hospital building are impacting patients. This review suggests that there is a need for future interdisciplinary collaborative research to quantify the optimum range for HVAC parameters considering airborne exposures and patients' positive medical outcomes.

Modeling the Airborne Infection Risk of Tuberculosis for a Research Facility in eMalahleni, South Africa

A detailed mathematical modeling framework for the risk of airborne infectious disease transmission in indoor spaces was developed to enable mathematical analysis of experiments conducted at the Airborne Infections Research (AIR) facility, eMalahleni, South Africa. A model was built using this framework to explore possible causes of why an experiment at the AIR facility did not produce expected results. The experiment was conducted at the AIR facility from August 31, 2015 to December 4, 2015, in which the efficacy of upper room germicidal ultraviolet (GUV) irradiation as an environmental control was tested. However, the experiment did not produce the expected outcome of having fewer infections in the test animal room than the control room. The simulation results indicate that dynamic effects, caused by switching the GUV lights, power outages, or introduction of new patients, did not result in the unexpected outcomes. However, a sensitivity analysis highlights that significant uncertainty exists with risk of transmission predictions based on current measurement practices, due to the reliance on large viable literature ranges for parameters.

Ambient air pollution exposures and risk of drug-resistant tuberculosis

BACKGROUND

Few epidemiological studies have explored the effects of air pollution on the risk of drug-resistant tuberculosis (DR-TB).

OBJECTIVE

To investigate the short and long term residential concentrations of ambient air pollutants (particulate matter <10 μm in diameter (PM₁₀) and particulate matter≤2.5 μm in diameter (PM_2.5), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), ozone (O₃), and carbon monoxide (CO)) in relation to the risk of DR-TB in a typical air pollution city, Jinan city, China.

METHODS

A total of 752 new culture-confirmed TB cases reported in TB prevention and control institutions of Jinan from January 1, 2014 to December 31, 2015 were included. Average individual-level concentrations of air pollution for 5 different exposure windows, vary from 90 days to 720 days to diagnosis were estimated using measurements from monitor closest to the patient home addresses. Logistic regression model adjusted for potential confounders was employed to evaluate correlation between air pollution and DR-TB risk at different five exposure windows individually.

RESULTS

There were substantially increased mono-drug resistance and poly-drug resistance risks for ambient PM_2.5, PM₁₀, O₃, and CO exposures. High exposure to PM_2.5, PM₁₀, and CO was also significantly associated with increased incidence of multi-drug resistance (MDR) both in the single- and multi-pollutants regression models. The dominant positive associations for PM_2.5was observed at 540 days exposure, for O₃ was observed at 180 days exposure, and for PM₁₀ and CO was observed from 90 days to 540 days exposures.

CONCLUSIONS

Our finding suggest that exposure to ambient air pollution (PM_2.5, PM₁₀, O₃, and CO) are associated with increased risk of DR-TB. We provided epidemiological evidence of association between pollution exposure and mono-, poly- and multi-drug resistance.

Assessing the Dynamics and Control of Droplet- and Aerosol-Transmitted Influenza Using an Indoor Positioning System

There is increasing evidence that aerosol transmission is a major contributor to the spread of influenza. Despite this, virtually all studies assessing the dynamics and control of influenza assume that it is transmitted solely through direct contact and large droplets, requiring close physical proximity. Here, we use wireless sensors to measure simultaneously both the location and close proximity contacts in the population of a US high school. This dataset, highly resolved in space and time, allows us to model both droplet and aerosol transmission either in isolation or in combination. In particular, it allows us to computationally quantify the potential effectiveness of overlooked mitigation strategies such as improved ventilation that are available in the case of aerosol transmission. Our model suggests that recommendation-abiding ventilation could be as effective in mitigating outbreaks as vaccinating approximately half of the population. In simulations using empirical transmission levels observed in households, we find that bringing ventilation to recommended levels had the same mitigating effect as a vaccination coverage of 50% to 60%. Ventilation is an easy-to-implement strategy that has the potential to support vaccination efforts for effective control of influenza spread.

Recognition of aerosol transmission of infectious agents: a commentary

Although short-range large-droplet transmission is possible for most respiratory infectious agents, deciding on whether the same agent is also airborne has a potentially huge impact on the types (and costs) of infection control interventions that are required.The concept and definition of aerosols is also discussed, as is the concept of large droplet transmission, and airborne transmission which is meant by most authors to be synonymous with aerosol transmission, although some use the term to mean either large droplet or aerosol transmission.However, these terms are often used confusingly when discussing specific infection control interventions for individual pathogens that are accepted to be mostly transmitted by the airborne (aerosol) route (e.g. tuberculosis, measles and chickenpox). It is therefore important to clarify such terminology, where a particular intervention, like the type of personal protective equipment (PPE) to be used, is deemed adequate to intervene for this potential mode of transmission, i.e. at an N95 rather than surgical mask level requirement.With this in mind, this review considers the commonly used term of 'aerosol transmission' in the context of some infectious agents that are well-recognized to be transmissible via the airborne route. It also discusses other agents, like influenza virus, where the potential for airborne transmission is much more dependent on various host, viral and environmental factors, and where its potential for aerosol transmission may be underestimated.

Recognition of aerosol transmission of infectious agents: a commentary

Although short-range large-droplet transmission is possible for most respiratory infectious agents, deciding on whether the same agent is also airborne has a potentially huge impact on the types (and costs) of infection control interventions that are required.The concept and definition of aerosols is also discussed, as is the concept of large droplet transmission, and airborne transmission which is meant by most authors to be synonymous with aerosol transmission, although some use the term to mean either large droplet or aerosol transmission.However, these terms are often used confusingly when discussing specific infection control interventions for individual pathogens that are accepted to be mostly transmitted by the airborne (aerosol) route (e.g. tuberculosis, measles and chickenpox). It is therefore important to clarify such terminology, where a particular intervention, like the type of personal protective equipment (PPE) to be used, is deemed adequate to intervene for this potential mode of transmission, i.e. at an N95 rather than surgical mask level requirement.With this in mind, this review considers the commonly used term of 'aerosol transmission' in the context of some infectious agents that are well-recognized to be transmissible via the airborne route. It also discusses other agents, like influenza virus, where the potential for airborne transmission is much more dependent on various host, viral and environmental factors, and where its potential for aerosol transmission may be underestimated.

Impact of air-handling system exhaust failure on dissemination pattern of simulant pathogen particles in a clinical biocontainment unit

Biocontainment units (BCUs) are facilities used to care for patients with highly infectious diseases. However, there is limited guidance on BCU protocols and design. This study presents the first investigation of how HVAC (heating, ventilation, air-conditioning) operating conditions influence the dissemination of fluorescent tracer particles released in a BCU. Test conditions included normal HVAC operation and exhaust failure resulting in loss of negative pressure. A suspension of optical brightener powder and water was nebulized to produce fluorescent particles simulating droplet nuclei (0.5-5 μm). Airborne particle number concentrations were monitored by Instantaneous Biological Analyzers and Collectors (FLIR Systems). During normal HVAC operation, fluorescent tracer particles were contained in the isolation room (average concentration = 1 × 10⁴ ± 3 × 10³ /L_air ). Under exhaust failure, the automated HVAC system maximizes airflow into areas adjacent to isolation rooms to attempt to maintain negative pressure differential. However, 6% of the fluorescent particles were transported through cracks around doors/door handles out of the isolation room via airflow alone and not by movement of personnel or doors. Overall, this study provides a systematic method for evaluating capabilities to contain aerosolized particles during various HVAC scenarios. Recommendations are provided to improve situation-specific BCU safety.

The influence of air-dispersed essential oils from lemon (Citrus limon) and silver fir (Abies alba) on airborne bacteria and fungi in hospital rooms

Airborne bacteria and fungi are an ongoing problem in hospitals. Because of the antimicrobial activities of essential oils (EOs) dispersion of EOs into the air may help to reduce this contamination. The aim of this study was to evaluate the efficacy of the dispersion of selected EOs in reducing the microbial contamination in two hospital wards. The study was carried out at two wards of a 1,227-bed acute-care hospital in Austria. The concentration of airborne bacteria and fungi was measured in patient rooms before and after dispersion of a mixture of Citrus limon EO and Abies alba EO. Before dispersion of the EOs in both wards the mean concentration of bacteria was in a typical range (123 colony forming units (CFU) m^-3 and 104 CFU m^-3) while the mean concentration of fungi differed substantially (155 CFU m^-3 and 28 CFU m^-3). After dispersion of the EOs, a reduction in both bacterial and fungal contamination was observed. In the first two hours the mean concentration of airborne bacteria and fungi was reduced by approximately 40% and 30%-60% respectively. The selected EO mixture is effective in reducing the microbial contamination of the indoor air.

Sick Building Syndrome and Other Building-Related Illnesses

Sick building syndrome (SBS) and building-related illnesses are omnipresent in modern high-rise buildings. The SBS is a complex spectrum of ill health symptoms, such as mucous membrane irritation, asthma, neurotoxic effects, gastrointestinal disturbance, skin dryness, sensitivity to odours that may appear among occupants in office and public buildings, schools and hospitals. Studies on large office buildings from USA, UK, Sweden, Finland, Japan, Germany, Canada, China, India, Netherlands, Malaysia, Taiwan, and Thailand, substantiate the occurrence of SBS phenomena. The accumulated effects of a multitude of factors, such as the indoor environmental quality, building characteristics, building dampness, and activities of occupants attribute to SBS. A building occupant manifests at least one symptom of SBS, the onset of two or more symptoms at least twice, and rapid resolution of symptoms following moving away from the workstation or building may be defined as having SBS. Based on the peer-reviewed documentation, this chapter elaborates the magnitude of building-related health consequences due to measurable environmental causations, and the size of the population affected. The mechanisms and causative factors of SBS and illnesses include, for example, the oxidative stress resulting from indoor pollutants, VOCs, office work-related stressors, humidification, odours associated with moisture and bioaerosol exposure. Related regulatory standards and strategies for management of SBS and other illnesses are elaborated.

Strict Isolation

Strict isolation: suspected highly infectious and transmissible virulent and pathogenic microbes, highly resistant bacterial strains and agents that are not accepted in any form of distribution in the society or in the environment. Examples are completely resistant Mycobacterium tuberculosis, viral haemorrhagic fevers like Ebola and Lassa, pandemic severe influenza and coronavirus like SARS, MERS, etc. In most countries, strict isolation is a rarely used isolation regime but should be a part of the national preparedness plan. For instance, in Norway, strict isolation has not been used for the last 50–60 years, except for one case of imported Ebola infection in 2014. Patients in need of strict isolation should be placed in a separate isolation ward or building.

Infection spread by contact, droplet and airborne infection, aerosols, re-aerosols, airborne microbe-carrying particles, skin cells, dust, droplets and droplet nuclei. At the same time, it is always contact transmission (contaminated environment, equipment, textiles and waste).

The source of infection is usually a patient but may also be a symptomless carrier or a zoonotic disease.

Background Information: Isolation Routines

The isolation of patients with suspected or documented infections—to not spread to others—has been discussed for hundreds of years. Guidelines are many, methods are different, attitudes show vide variations, routines and procedures are still changing, regulations by law may be absent, and some healthcare professionals may be afraid of adverse outcomes of isolation [1–44]. Microbes that are spread in the environment, on the hands and equipment are invisible. The invisible agent does not call on attention before the infection; clinical disease, hospital infection or nosocomial infection is a factum that can be registered [23, 28, 29, 35–37]. How to stop the transmission is often “to believe and not believe” in infection control.

Protection of Upper Respiratory Tract, Mouth and Eyes

Pathogenic bacteria and viruses may invade via upper and lower respiratory tract and via eye mucosa. When an infected person coughs or sneezes heavily, small, invisible droplets with the infective agent may reach a good distance from the source. By using the right form of protection at the right time, infection and disease are prevented. The present chapter is focused on the protection against airborne infections.

Assessment of the ventilation efficiency in the breathing zone during sleep through computational fluid dynamics techniques

In developed countries, presence at home varies between 60% and 90% of the day, sleeping supposes 30%. Therefore, it is essential to ensure good indoor air quality that enhances health and benefits rest and recovery. In this context, it is necessary to achieve a balance between energy efficiency and air distribution parameters; thus, the influence exerted by the furniture of a bedroom on the air exchange efficiency, in the breathing zone during sleep, is assessed in this study. Computational fluid dynamics techniques, experimentally validated by the tracer gas (SF6) concentration decay method, are used to analyze 52 case studies corresponding to the same space, but varying both the number and the arrangement of the furniture inside. It is concluded that, in order to achieve a significant improvement in the air exchange efficiency, the number of elements included in the bedroom is not relevant, but the position of them. The highest increase in the ventilation efficiency in breathing zone is observed when the furniture is located avoiding the airflow obstruction in the area near the inlet and creating an unfilled volume of air in the area close to the outlet.

Indoor Air Quality and Sustainability Management—Case Study in Three Portuguese Healthcare Units

Adequate management of indoor air quality (IAQ) in healthcare units has relevant impacts on sustainability performance due to its effects on patient safety, occupational health and safety, and energy consumptions. This study sought to identify improvement opportunities on IAQ management by collecting and analyzing experimental data of selected parameters in three healthcare units in Portugal: Two general hospitals and one primary healthcare center. Indoor air temperature, relative humidity, CO2, bacteria, and fungi concentrations were measured in summer and winter campaigns in June/July 2017 and in January/March 2018. Results show that the exclusive use of natural ventilation is not adequate when the affluence of users is high, but the analyzed parameters revealed acceptable results under low occupation intensity conditions. Results also show that keeping low indoor air relative humidity has a significant impact in reducing fungi concentration and that there is a significant correlation at the 0.05 level between indoor air CO2 concentration and bacterial loads. Therefore, as opportunities to improve sustainability, IAQ management in healthcare facilities should consider natural ventilation as a complement to mechanical ventilation systems and should focus on adequate control of indoor air relative humidity and CO2 concentration to reduce the risk of airborne infections.

Bacillus species at the Canberra Airport: A comparison of real-time polymerase chain reaction and massively parallel sequencing for identification

Anthrax, caused by the Gram-positive, spore forming bacterium Bacillus anthracis, is a disease with naturally occurring outbreaks in many parts of the world, primarily in domestic and wild herbivores. Due to the movement of people and stock, B. anthracis could, however, be at transportation hubs including airports. The continuous threat to national and international security from a biological agent release, or hoax attack, is a very real concern. Sensitive, robust and rapid (hours-day) methods to identify biological agents, including B. anthracis, and distinguish pathogenic from non-pathogenic species, is an essential cornerstone to national security. The aim of this project was to determine the presence of Bacillus species at the Canberra Airport using two massively parallel sequencing (MPS) approaches and compare with previous results using real-time polymerase chain reaction (qPCR). Samples were collected daily for seven days each month from August 2011-July 2012 targeting movement of people, luggage and freight into and out of the Canberra Airport. Extracted DNA was analysed using qPCR specific for B. anthracis. A subset of samples was analysed using two MPS approaches. Approach one, using the Ion PGM™ (Thermo Fisher Scientific; TFS) and an in-house assay, targeted the two B. anthracis virulence plasmids (cya and capB genes) and a single conserved region of the 16S rRNA gene. Approach two, using the Ion S5™ (TFS) and the commercial Ion 16S™ Metagenomics Kit (TFS), targeted multiple regions within the bacterial 16S rRNA gene. Overall there was consistency between the two MPS approaches and between MPS and qPCR, however, MPS was more sensitive, particularly for plasmid detection. Whilst the broad-range 16S genomic target(s) used in both MPS approaches in this study was able to generate a metagenomic fingerprint of the bacterial community at the Canberra Airport, it could not resolve Bacillus species beyond the level of the Bacillus cereus group. The inclusion of B. anthracis virulence plasmid targets in the in-house assay did allow for the potential presumptive identifications of pathogenic species. No plasmid targets were in the Ion 16S™ Metagenomics Kit. This study shows the choice of target(s) is key in MPS assay development and should be carefully considered to ensure the assay is fit for purpose, whether as an initial screening (presumptive) or a more specific (but not entirely confirmatory) test. Identification approaches may also benefit from a combination of MPS and qPCR as each has benefits and limitations.

Bioaerosol Sampler Choice Should Consider Efficiency and Ability of Samplers To Cover Microbial Diversity

Bioaerosol studies aim to describe the microbial content and increase understanding of the aerosolization processes linked to diseases. Air samplers are used to collect, identify, and quantify bioaerosols. Studies comparing the performances of air samplers have typically used a culture approach or have targeted a specific microorganism in laboratory settings. The objective of this study was to use environmental field samples to compare the efficiencies of 3 high-airflow-rate samplers for describing bioaerosol diversity using a next-generation sequencing approach. Two liquid cyclonic impactors and one electrostatic filter dry sampler were used in four wastewater treatment plants to target bacterial diversity and in five dairy farms to target fungal diversity. The dry electrostatic sampler was consistently more powerful in collecting more fungal and bacterial operational taxonomic units (OTUs). Substantial differences in OTU abundances between liquid and dry sampling were revealed. The majority of the diversity revealed by dry electrostatic sampling was not identified using the cyclonic liquid impactors. The findings from this work suggest that the choice of a bioaerosol sampler should include information about the efficiency and ability of samplers to cover microbial diversity. Although these results suggest that electrostatic filters result in better coverage of the microbial diversity among the tested air samplers, further studies are needed to confirm this hypothesis. While it is difficult to determine a single universally optimal air sampler, this work provides an in-depth look at some of the considerations that are essential when choosing an air sampler for studying the microbial ecology of bioaerosols.IMPORTANCE Associating bioaerosol exposure and health problems is challenging, and adequate exposure monitoring is a priority for scientists in the field. Conclusions that can be drawn from bioaerosol exposure studies are highly dependent on the design of the study and the methodologies used. The air sampling strategy is the first methodological step leading to an accurate interpretation of what is present in the air. Applying new molecular approaches to evaluate the efficiencies of the different types of samplers used in the field is necessary in order to circumvent traditional approaches and the biases they introduce to such studies. The results and conclusions provided in this paper should be taken in consideration when conducting a bioaerosol study.

Performance of the original workstation for aerosol tests under controlled conditions

Air quality monitoring is essential when it comes to protecting the urban population, especially that of big metropolises, from biohazards including biopathogens (BPs). This process is aided by different samplers and analyzers of aerosol pollutants, filters and disinfection systems. Their performance is tested using experimental aerosol formulations with a predetermined composition. Unfortunately, the majority of such systems available in Russia are only able to process a few hundred liters of air per time unit, which is too little. Big aerosol chambers (10 to 20 m3) are very expensive and may not fit into a lab, necessitating an extensive overhaul. In this work we present a workstation for the detection of BP markers under controlled conditions based on the microbiological safety box MSB-III-Laminar-C-1.5 (380.150.01) that was originally designed to test the performance of samplers and analyzers of experimental aerosol formulations. Our workstation can handle the majority of BSL-1-2 BPs and, given the chamber volume that satisfies the requirements of aerosol experiments (> 4 m3), can be installed in a lab with an area of >10 m2.

Passively transferred M2e-specific monoclonal antibody reduces influenza A virus transmission in mice

Influenza represents a global public health threat. Currently available influenza vaccines are effective against strain-matched influenza A and B viruses but do not protect against novel pandemic viruses. Vaccine candidates that target conserved B or T cell epitopes of influenza viruses could circumvent this shortcoming. The conserved extracellular domain of matrix protein 2 (M2e) of influenza A is an example of such a broadly protective vaccine candidate. Protection by M2e-based vaccine candidates largely depends on M2e-specific IgG antibodies. Here we show that the M2e-specific IgG2a monoclonal antibody 65 (MAb 65) can reduce influenza A/Udorn/72 (H3N2) and A/Hong Kong/68 (H3N2) virus plaque formation. This effect was not observed with other influenza A virus strains tested. We further show that passive transfer of MAb 65 to mice can reduce viral loads in the upper and lower airways, which results in reduced transmission of A/Udorn/72 and A/Hong Kong/68 viruses to cohoused, unimmunized contact mice. Virus restriction by passively transferred Mab 65 was significantly less pronounced in Fcgr1^-/-Fcgr3^-/- mutant mice compared with wild type controls, suggesting that in vivo protection provided by MAb 65 depends on Fcγ receptor-mediated antibody effector mechanisms. We conclude that M2e-based antibody immune therapy has the potential to diminish influenza A virus replication in the immunized host as well as in exposed naïve contacts.

Airborne spread of expiratory droplet nuclei between the occupants of indoor environments: A review

This article reviews past studies of airborne transmission between occupants in indoor environments, focusing on the spread of expiratory droplet nuclei from mouth/nose to mouth/nose for non-specific diseases. Special attention is paid to summarizing what is known about the influential factors, the inappropriate simplifications of the thermofluid boundary conditions of thermal manikins, the challenges facing the available experimental techniques, and the limitations of available evaluation methods. Secondary issues are highlighted, and some new ways to improve our understanding of airborne transmission indoors are provided. The characteristics of airborne spread of expiratory droplet nuclei between occupants, which are influenced correlatively by both environmental and personal factors, were widely revealed under steady-state conditions. Owing to the different boundary conditions used, some inconsistent findings on specific influential factors have been published. The available instrumentation was too slow to provide accurate concentration profiles for time-dependent evaluations of events with obvious time characteristics, while computational fluid dynamics (CFD) studies were mainly performed in the framework of inherently steady Reynolds-averaged Navier-Stokes modeling. Future research needs in 3 areas are identified: the importance of the direction of indoor airflow patterns, the dynamics of airborne transmission, and the application of CFD simulations.

Ventilation control for airborne transmission of human exhaled bio-aerosols in buildings

The emergence of respiratory diseases, i.e., severe acute respiratory syndrome (SARS) epidemic in 2003, H1N1 influenza epidemic in 2011 and Middle East respiratory syndrome (MERS) outbreak, reiterated the significance of ventilation in buildings. The role of ventilation in removing exhaled airborne bio-aerosols and preventing cross infections has been multidisciplinary extensively studied after the SARS outbreak in 2003. The characteristics of droplet-borne, short-range airborne and long-range airborne transmission of infectious diseases were identified. Increasing ventilation rate can effectively reduce the risk of long-range airborne transmission, while it may be of little useful in preventing the droplet-borne transmission. To maintain the airflow direction from clean cubicles to dirty cubicles is an effective way to prevent the cross infection between cubicles, which is widely used in hospital isolation rooms. Field measurements showed that wrong air flow direction was due to poor construction quality or maintenance. The impacts of different airflow patterns on removing large droplets and fine droplet nuclei were discussed. Some new concepts in general ventilation systems and local personalized equipment were also introduced. This review updates current knowledge of the airborne transmission of pathogens and the improvement of ventilation efficiency concerning the infection prevention.

An innovative personalized displacement ventilation system for airliner cabins

In airliner cabins, mixing ventilation systems with gaspers are not efficient in controlling contaminant transport. To improve the cabin environment, this investigation proposed an innovative ventilation system that would reduce contaminant transport and maintain thermal comfort. We manufactured and installed the proposed ventilation system in an occupied seven-row, single-aisle aircraft cabin mockup. Air velocity, air temperature, and contaminant distribution in the cabin mockup were obtained by experimental measurements. The investigation used the experimental data to validate the results of CFD simulation. The validated CFD program was then used to study the impact of the locations and number of exhausts on contaminant removal and thermal comfort in a one-row section of a fully occupied Boeing-737 cabin. Although the diffusers in the proposed system were close to the passengers' legs, the air velocity magnitude was acceptable in the lower part of the cabin and the leg area. The proposed system provided an acceptable thermal environment in the cabin, although passengers could feel cold when placing their legs directly in front of the diffusers. The four-exhaust configuration of the new ventilation system was the best, and it decreased the average exposure in the cabin by 57% and 53%, respectively, when compared with the mixing and displacement ventilation systems.

CFD investigation on the effects of wind and thermal wall-flow on pollutant transmission in a high-rise building

The solar radiation can heat the building outer surface, and then cause the upward natural convection flows adjacent to the wall. This phenomenon is especially obvious on a windless sunny day. The near wall thermal plume can drive gaseous pollutants released from lower floors to upper floors. Combined with the effect of ambient approaching wind, the transmission routes will be very complicated. The paper aims to investigate the airflow patterns and pollutant transmission within a building under the effects of wind and thermal forces. A hypothetical twenty-storey slab-shape high-rise building in Shanghai with single-sided natural ventilation is set as the research object in the present study. The intensity of solar radiation on a typical day during transition season is theoretically analysed. The temperature difference between the heated building envelope and the ambient air is calculated by a simplified heat balance model. Finally, the tracer gas method is employed in the numerical simulation to analyse the influence of the wind and wall thermal plume flow on the inter-flat pollutant transmission characteristics. The results show that, the temperature difference between sunward and shady side wall is about 10 K at noon on the designate day. When the source is set as a point with steady intensity and the buoyancy is stronger than or approximately equivalent to the wind, the reentry ratio of the flat immediately above the source can be around 25%.

Cleaning the air with ultraviolet germicidal irradiation lessened contact infections in a long-term acute care hospital

BACKGROUND

This study was designed to determine whether removing bacteria from the air with ultraviolet germicidal irradiation (UV-C) at the room level would reduce infection rates.

METHODS

We reviewed infection data for 12 months before and after UV-C installation in the special care unit (SCU) of a long-term acute care hospital. All patients admitted to the SCU during the study time frame were included. Microbiologic impactor air sampling was completed in August 2015. Shielded UV-C units were installed in 16 patient rooms, the hallway, and the biohazard room. Air sampling was repeated 81 days later.

RESULTS

After UV-C installation, airborne bacteria (colony forming units [CFU] per cubic meter of air) in patient rooms were reduced an average of 42% (175 vs 102 CFU/m³). Common health care-associated infections (HAIs) (Clostridium difficile [8 cases annually vs 1 case, P = .01] and catheter-associated urinary tract infection [20 cases annually vs 9 cases, P = .012]) were reduced significantly as were overall infections, in number of cases (average 8.8 per month vs 3.5, P < .001), and infection rate (average monthly rate 20.3 vs 8.6, P = .001), despite no reported changes to the amount or type of cleaning done, infection control protocols, or reporting procedures. Other infections, traditionally considered contact transmissible (central line-associated bloodstream infection and methicillin-resistant Staphylococcus aureus), also declined noticeably.

CONCLUSIONS

Continuous shielded UV-C reduced airborne bacteria and may also lower the number of HAIs, including those caused by contact pathogens. Reduced infections result in lessened morbidity and lower costs. Health care facilities might wish to consider continuous shielded UV-C at the room level as a possible addition to their infection prevention and control protocols.

A simple method for differentiating direct and indirect exposure to exhaled contaminants in mechanically ventilated rooms

Many airborne infectious diseases can be transmitted via exhaled contaminants transported in the air. Direct exposure occurs when the exhaled jet from the infected person directly enters the breathing zone of the target person. Indirect exposure occurs when the contaminants disperse in the room and are inhaled by the target person. This paper presents a simple method for differentiating the direct and indirect exposure to exhaled contaminants in mechanically ventilated rooms. Experimental data for 191 cases were collected from the literature. After analyzing the data, a simple method was developed to differentiate direct and indirect exposure in mixing and displacement ventilated rooms. The proposed method correctly differentiated direct and indirect exposure for 120 out of the 133 mixing ventilation cases and 47 out of the 58 displacement ventilation cases. Therefore, the proposed method is suitable for use at the early design stage to quickly assess whether there will be direct exposure to exhaled contaminants in a mechanically ventilated room.

High-performance color sequence particle streak velocimetry for 3D airflow measurement

In this paper, a high-performance color sequence particle streak velocimetry (CSPSV) technique is proposed to measure the air velocity in a large three-dimensional (3D) space. Based on the basic principle of CSPSV, a new color sequence illumination pattern is designed to mark seeding bubbles for better imaging performance. Synchronized with the illumination system, cameras record the targets' paths at the start, middle, and end points with different color information more clearly. Thus, a rectification-based stereo corresponding algorithm is presented to reconstruct the 3D trajectory of the bubbles. The accuracy of this system is verified and shows good consistency with a hot-wire anemometer (the principal research tool for turbulent-flow studies). The vortex test experiments also indicate its capability for complex airflow. Our high-performance CSPSV can extend the 3D measurement zone from several cubic centimeters to several cubic meters with regular, off-the-shelf cameras.

Seasonal variation of window opening behaviors in two naturally ventilated hospital wards

Natural ventilation enables personal control, and occupant behaviors in window opening play a decisive role on natural ventilation performance, indoor air quality (IAQ), and/or airborne infection risk in a hospital setting. The occupant behaviors differ significantly from different building types with different functions and living habits. Based on a one-year field measurement in two general hospital wards in Nanjing, China, the effects of air quality (i.e. indoor CO2 concentration and outdoor PM2.5 concentration) and the climatic parameters (i.e. indoor/outdoor temperature, relative humidity, and outdoor wind speed, wind direction and rainfall) on window opening/closing behaviors are analyzed. Indoor air temperature or relative humidity is found to be a dominant factor for window opening behaviors. Seasonal differences are observed for the different influences of physical factors. The outdoor temperature is found to be associated with the window opening probability negatively during the cooling season, but positively during the transition and heating seasons. The indoor relative humidity positively affects the window opening probability during the transition season while a negative impact appears during the cooling and heating seasons. Based on the seasonal variation of window opening behaviors, Logistic regression models in different seasons (cooling, transition and heating seasons) are developed to predict the window opening/closing state and are verified to be promisingly adaptable with results of accuracy bigger than 70%.

Measuring ventilation and modelling M. tuberculosis transmission in indoor congregate settings, rural KwaZulu-Natal

SETTING: Molecular epidemiology suggests that most Mycobacterium tuberculosis transmission in high-burden settings occurs outside the home.

OBJECTIVE: To estimate the risk of M. tuberculosis transmission inside public buildings in a high TB burden community in KwaZulu-Natal, South Africa.

DESIGN: Carbon dioxide (CO₂) sensors were placed inside eight public buildings. Measurements were used with observations of occupancy to estimate infection risk using an adaptation of the Wells-Riley equation. Ventilation modelling using CONTAM was used to examine the impact of low-cost retrofits on transmission in a health clinic.

RESULTS: Measurements indicate that infection risk in the church, classroom and clinic waiting room would be high with typical ventilation, occupancy levels and visit durations. For example, we estimated that health care workers in a clinic waiting room had a 16.9–24.5% annual risk of M. tuberculosis infection. Modelling results indicate that the simple addition of two new windows allowing for cross-ventilation, at a cost of US$330, would reduce the annual risk to health care workers by 57%.

CONCLUSIONS: Results indicate that public buildings in this community have a range of ventilation and occupancy characteristics that may influence transmission risks. Simple retrofits may result in dramatic reductions in M. tuberculosis transmission, and intervention studies should therefore be considered.

Building Evidence for Health: Green Buildings, Current Science, and Future Challenges

Civilizational challenges have questioned the status quo of energy and material consumption by humans. From the built environment perspective, a response to these challenges was the creation of green buildings. Although the revolutionary capacity of the green building movement has elevated the expectations of new commercial construction, its rate of implementation has secluded the majority of the population from its benefits. Beyond reductions in energy usage and increases in market value, the main strength of green buildings may be the procurement of healthier building environments. Further pursuing the right to healthy indoor environments could help the green building movement to attain its full potential as a transformational public health tool. On the basis of 40 years of research on indoor environmental quality, we present a summary of nine environment elements that are foundational to human health. We posit the role of green buildings as a critical research platform within a novel sustainability framework based on social-environmental capital assets.

Numerical and experimental study on airborne disinfection by negative ions in air duct flow

In this paper, we develop a mathematical model that aims (1) to predict the distribution of negative ions generated by an air ionizer installed in a ventilation duct and (2) to predict the efficiency with which it inactivates bacteria. The transportation equation for the negative ions was resolved combined with the bulk air velocity and the electric field. The bacteria distribution was solved numerically by integrating the susceptibility constant, which was acquired from the experiments. Two types of bacteria (Serratia marcescens, Staphylococcus epidermidis) were aerosolized and released into a 9-m ventilation duct system. Inactivation efficiencies were calculated for inlet velocities from 2 to 6.5 m/s and for various ion intensities. The efficiencies for S. marcescens and S. epidermidis were 31.53% (SD, 11.4%) and 12.17% (SD, 0.43%), respectively, with susceptibility constants of 8.67 × 10-11 Colony-Forming Units (CFU)/ions and 2.72 × 10-11 CFU/ions, respectively. The modeling results matched those of the experiments well. The pressure penalty at the maximum velocity (6.5 m/s) was only 9 Pa. The results show that the use of negative ions has great potential to enhance indoor air quality by reducing airborne microorganisms in ventilation systems.

The Fate of Mengovirus on Fiberglass Filter of Air Handling Units

One of the most important topics that occupy public health problems is the air quality. That is the reason why mechanical ventilation and air handling units (AHU) were imposed by the different governments in the collective or individual buildings. Many buildings create an artificial climate using heating, ventilation, and air-conditioning systems. Among the existing aerosols in the indoor air, we can distinguish the bioaerosol with biological nature such as bacteria, viruses, and fungi. Respiratory viral infections are a major public health issue because they are usually highly infective. We spend about 90% of our time in closed environments such as homes, workplaces, or transport. Some studies have shown that AHU contribute to the spread and transport of viral particles within buildings. The aim of this work is to study the characterization of viral bioaerosols in indoor environments and to understand the fate of mengovirus eukaryote RNA virus on glass fiber filter F7 used in AHU. In this study, a set-up close to reality of AHU system was used. The mengovirus aerosolized was characterized and measured with the electrical low pressure impact and the scanner mobility particle size and detected with RT-qPCR. The results about quantification and the level of infectivity of mengovirus on the filter and in the biosampler showed that mengovirus can pass through the filter and remain infectious upstream and downstream the system. Regarding the virus infectivity on the filter under a constant air flow, mengovirus was remained infectious during 10 h after aerosolization.

A comparison between tracer gas and aerosol particles distribution indoors: The impact of ventilation rate, interaction of airflows, and presence of objects

The study investigated the separate and combined effects of ventilation rate, free convection flow produced by a thermal manikin, and the presence of objects on the distribution of tracer gas and particles in indoor air. The concentration of aerosol particles and tracer gas was measured in a test room with mixing ventilation. Three layouts were arranged: an empty room, an office room with an occupant sitting in front of a table, and a single-bed hospital room. The room occupant was simulated by a thermal manikin. Monodisperse particles of three sizes (0.07, 0.7, and 3.5 μm) and nitrous oxide tracer gas were generated simultaneously at the same location in the room. The particles and gas concentrations were measured in the bulk room air, in the breathing zone of the manikin, and in the exhaust air. Within the breathing zone of the sitting occupant, the tracer gas emerged as reliable predictor for the exposure to all different-sized test particles. A change in the ventilation rate did not affect the difference in concentration distribution between tracer gas and larger particle sizes. Increasing the room surface area did not influence the similarity in the dispersion of the aerosol particles and the tracer gas.

Bacterial diversity among four healthcare-associated institutes in Taiwan

Indoor microbial communities have important implications for human health, especially in health-care institutes (HCIs). The factors that determine the diversity and composition of microbiomes in a built environment remain unclear. Herein, we used 16S rRNA amplicon sequencing to investigate the relationships between building attributes and surface bacterial communities among four HCIs located in three buildings. We examined the surface bacterial communities and environmental parameters in the buildings supplied with different ventilation types and compared the results using a Dirichlet multinomial mixture (DMM)-based approach. A total of 203 samples from the four HCIs were analyzed. Four bacterial communities were grouped using the DMM-based approach, which were highly similar to those in the 4 HCIs. The α-diversity and β-diversity in the naturally ventilated building were different from the conditioner-ventilated building. The bacterial source composition varied across each building. Nine genera were found as the core microbiota shared by all the areas, of which Acinetobacter, Enterobacter, Pseudomonas, and Staphylococcus are regarded as healthcare-associated pathogens (HAPs). The observed relationship between environmental parameters such as core microbiota and surface bacterial diversity suggests that we might manage indoor environments by creating new sanitation protocols, adjusting the ventilation design, and further understanding the transmission routes of HAPs.

Dynamic interaction of a downward plane jet and a cough jet with respect to particle transmission: An analytical and experimental study

A cough jet can travel beyond the breathing zone of the source person, and thus, infectious viral- and bacterial-laden particles can be transported from the source person to others in close proximity. To reduce the interpersonal transmission of coughed particles, the objective of this study was to analytically and experimentally investigate the performance of downward plane jets with various discharge velocities. Chamber measurements were conducted to examine the interaction between a transient cough jet (discharge velocities of 12 m/sec and 16 m/sec) and a steady downward plane jet (discharge velocities from 1.0-8.5 m/sec) with respect to the transport of and human exposure to coughed particles. The results show that a relatively high-speed cough can easily penetrate a downward plane jet with a discharge velocity of less than 6 m/sec. A downward plane jet with a discharge velocity of 8.5 m/sec can bend the cough jet to a certain extent. In this study, momentum comparison of the cough jet and the downward plane jet shows that the value of personal exposure to coughed particles depends on the ratio of jet momentums. The results show that when the two momentums are equivalent or if the downward plane jet has a greater momentum, the cough jet is deflected downward and does not reach the breathing zone of the target thermal dummy. Using the ratio of the two momentums, it may be estimated whether the transmission of a cough jet can be controlled. A trajectory model was developed based on the ratio of the two momentums of a cough jet and a downward jet and was validated using the experimental data. In addition, the predicted trajectory of the cough jet agreed well with the results from smoke visualization experiments. This model can be used to guide the design of downward plane jet systems for protection of occupants from coughed particles.

Pilot Intervention Study of Household Ventilation and Fine Particulate Matter Concentrations in a Low-Income Urban Area, Dhaka, Bangladesh

Fine particulate matter (PM_2.5) is a risk factor for pneumonia; ventilation may be protective. We tested behavioral and structural ventilation interventions on indoor PM_2.5 in Dhaka, Bangladesh. We recruited 59 good ventilation (window or door in ≥ 3 walls) and 29 poor ventilation (no window, one door) homes. We monitored baseline indoor and outdoor PM_2.5 for 48 hours. We asked all participants to increase ventilation behavior, including opening windows and doors, and operating fans. Where permitted, we installed windows in nine poor ventilation homes, then repeated PM_2.5 monitoring. We estimated effects using linear mixed-effects models and conducted qualitative interviews regarding motivators and barriers to ventilation. Compared with poor ventilation homes, good ventilation homes were larger, their residents wealthier and less likely to use biomass fuel. In multivariable linear mixed-effects models, ventilation structures and opening a door or window were inversely associated with the number of hours PM_2.5 concentrations exceeded 100 and 250 μg/m³. Outdoor air pollution was positively associated with the number of hours PM_2.5 concentrations exceeded 100 and 250 μg/m³. Few homes accepted window installation, due to landlord refusal and fear of theft. Motivators for ventilation behavior included cooling of the home and sunlight; barriers included rain, outdoor odors or noise, theft risk, mosquito entry, and, for fan use, perceptions of wasting electricity or unavailability of electricity. We concluded that ventilation may reduce indoor PM_2.5 concentrations but, there are barriers to increasing ventilation and, in areas with high ambient PM_2.5 concentrations, indoor concentrations may remain above recommended levels.

Air infiltration induced inter-unit dispersion and infectious risk assessment in a high-rise residential building

Identifying possible airborne transmission routes and assessing the associated infectious risks are essential for implementing effective control measures. This study focuses on the infiltration-induced inter-unit pollutant dispersion in a high-rise residential (HRR) building. The outdoor wind pressure distribution on the building facades was obtained from the wind tunnel experiments. And the inter-household infiltration and tracer gas transmission were simulated using multi-zone model. The risk levels along building height and under different wind directions were examined, and influence of component leakage area was analysed. It is found that, the cross-infection risk can be over 20% because of the low air infiltration rate below 0.7 ACH, which is significantly higher than the risk of 9% obtained in our previous on-site measurement with air change rate over 3 ACH. As the air infiltration rate increases along building height, cross-infection risk is generally higher on the lower floors. The effect of wind direction on inter-unit dispersion level is significant, and the presence of a contaminant source in the windward side results in the highest cross-infection risks in other adjacent units on the same floor. Properly improving internal components tightness and increasing air change via external components are beneficial to the control of internal inter-unit transmission induced by infiltration. However, this approach may increase the cross-infection via the external transmission, and effective control measures should be further explored considering multiple transmission routes.

Reflections on the history of indoor air science, focusing on the last 50 years

The scientific articles and Indoor Air conference publications of the indoor air sciences (IAS) during the last 50 years are summarized. In total 7524 presentations, from 79 countries, have been made at Indoor Air conferences held between 1978 (49 presentations) and 2014 (1049 presentations). In the Web of Science, 26 992 articles on indoor air research (with the word "indoor" as a search term) have been found (as of 1 Jan 2016) of which 70% were published during the last 10 years. The modern scientific history started in the 1970s with a question: "did indoor air pose a threat to health as did outdoor air?" Soon it was recognized that indoor air is more important, from a health point of view, than outdoor air. Topics of concern were first radon, environmental tobacco smoke, and lung cancer, followed by volatile organic compounds, formaldehyde and sick building syndrome, house dust-mites, asthma and allergies, Legionnaires disease, and other airborne infections. Later emerged dampness/mold-associated allergies and today's concern with "modern exposures-modern diseases." Ventilation, thermal comfort, indoor air chemistry, semi-volatile organic compounds, building simulation by computational fluid dynamics, and fine particulate matter are common topics today. From their beginning in Denmark and Sweden, then in the USA, the indoor air sciences now show increasing activity in East and Southeast Asia.

An easy tool to assess ventilation in health facilities as part of air-borne transmission prevention: a cross-sectional survey from Uganda

BACKGROUND

No guidelines exist on assessing ventilation through air changes per hour (ACH) using a vaneometer. The objective of the study was to evaluate the position and frequency for measuring air velocity using a vaneometer to assess ventilation with ACH; and to assess influence of ambient temperature and weather on ACH.

METHODS

Cross-sectional survey in six urban health facilities in Kampala, Uganda. Measurements consisted of taking air velocity on nine separate moments in five positions in each opening of the TB clinic, laboratory, outpatient consultation and outpatient waiting room using a vaneometer. We assessed in addition the ventilation with the "20% rule", and compared this estimation with the ventilation in ACH assessed using the vaneometer.

RESULTS

A total of 189 measurements showed no influence on air velocity of the position and moment of the measurement. No significant influence existed of ambient temperature and a small but significant influence of sunny weather. Ventilation was adequate in 17/24 (71%) of all measurements. Using the "20% rule", ventilation was adequate in 50% of rooms assessed. Agreement between both methods existed in 13/23 (56%) of the rooms assessed.

CONCLUSION

Most rooms had adequate ventilation when assessed using a vaneometer for measuring air velocity. A single vaneometer measurement of air velocity is adequate to assess ventilation in this setting. These findings provide practical input for clear guidelines on assessing ventilation using a vaneometer. Assessing ventilation with a vaneometer differs substantially from applying the "20% rule".

High temporal variability in airborne bacterial diversity and abundance inside single-family residences

Our homes are microbial habitats, and although the amounts and types of bacteria in indoor air have been shown to vary substantially across residences, temporal variability within homes has rarely been characterized. Here, we sought to quantify the temporal variability in the amounts and types of airborne bacteria in homes, and what factors drive this variability. We collected filter samples of indoor and outdoor air in 15 homes over 1 year (approximately eight time points per home, two per season), and we used culture-independent DNA sequencing approaches to characterize bacterial community composition. Significant differences in indoor air community composition were observed both between homes and within each home over time. Indoor and outdoor air community compositions were not significantly correlated, suggesting that indoor and outdoor air communities are decoupled. Indoor air communities from the same home were often just as different at adjacent time points as they were across larger temporal distances, and temporal variation correlated with changes in environmental conditions, including temperature and relative humidity. Although all homes had highly variable indoor air communities, homes with the most temporally variable communities had more stable, lower average microbial loads than homes with less variable communities.