Airborne Infectious Disease Transmission Research Articles

Movement Mechanisms and Numerical Simulation of Virus-containing Exhaled Droplets

The problem of viral and microbial contamination has received extensive and high attention from scholars at home and abroad. A great deal of information and research has demonstrated that droplets containing organisms such as viruses and bacteria can be airborne, so it is extremely important to study the movement and transmission patterns of the particles. Human coughing and sneezing are the main sources of viral droplets and are the focus of this paper. This topic starts with a theoretical approach to investigate the propagation law of microbial aerosols in the air, combined with the characteristics of droplets, to establish a model of microbial particle dispersal. And based on the Lagrangian method, the model is simplified and the 4th order standard Runge-Kutta algorithm is used to numerically solve the differential equations based on the Matlab platform, so as to analyse the effects of factors such as jet velocity, ambient wind speed and the size of the exhaled virus particles occurring on the particle motion. The evaporation of particles also has a relatively large effect on the motion of smaller sized particles, which after complete evaporation will will float in the air and will no longer hit the ground. Ultimately, the analysis of particle movement distances leads to recommendations for the prevention of airborne infectious disease transmission.

Multi-Scale Airborne Infectious Disease Transmission.

Airborne disease transmission is central to many scientific disciplines including agriculture, veterinary biosafety, medicine, and public health. Legal and regulatory standards are in place to prevent agricultural, nosocomial, and community airborne disease transmission. However, the overall importance of the airborne pathway is underappreciated, e.g.,, US National Library of Medicine's Medical Subjects Headings (MESH) thesaurus lacks an airborne disease transmission indexing term. This has practical consequences as airborne precautions to control epidemic disease spread may not be taken when airborne transmission is important, but unrecognized. Publishing clearer practical methodological guidelines for surveillance studies and disease outbreak evaluations could help address this situation.To inform future work, this paper highlights selected, well-established airborne transmission events - largely cases replicated in multiple, independently conducted scientific studies. Methodologies include field experiments, modeling, epidemiology studies, disease outbreak investigations and mitigation studies. Collectively, this literature demonstrates that airborne viruses, bacteria, and fungal pathogens have the capability to cause disease in plants, animals, and humans over multiple distances - from near range (< 5 m) to continental (> 500 km) in scale. The plausibility and implications of undetected airborne disease transmission are discussed, including the notable underreporting of disease burden for several airborne transmitted diseases.

The Effect on Fit of Multiple Consecutive Donning and Doffing of N95 Filtering Facepiece Respirators.

N95 filtering facepiece respirators (FFRs) are widely used in healthcare to reduce transmission of airborne infectious diseases. These respirators are generally described as single use or limited reuse devices, but cost and operational issues mean that they may be donned and doffed multiple times. There is scant research on the effect of this practice on adequacy of fit. The purpose of this study was to measure the effect on respirator fit of multiple donning and doffing of N95 FFRs. This was an experiment in which 16 women and 9 men employed by the National Institute for Occupational Health (NIOH), Johannesburg, donned their same N95 FFR six times. All 25 were trained in the correct wearing of the devices before the experiment. Four models of respirators were used: the six who did not use respirators at work (novice subjects) were issued a 3M 1860 FFR and the others used their currently supplied one. During the experiment subjects donned their respirators under the supervision of the tester. Quantitative fit testing was done in the NIOH Occupational Hygiene laboratory after each donning according to the OSHA-Accepted Fit Test Protocol using the TSI PortaCount Pro+ Model 8038 Respirator Fit Tester. During the test, fit was measured after each of seven exercises and then an overall fit factor was computed. Only individuals who achieved an initial overall fit factor of ≥100 were allowed to continue participation in the study. Median overall fit factors were calculated for the 25 subjects for each donning and changes across them was examined using Wilcoxon rank sum tests. Men and women and frequent and infrequent users were compared across the six tests. Infrequent use was defined as subjects who wore respirators ≤ once per week, and novice subjects. Two subjects (8%) had an overall fit factor <100 at fit Test 2, 6 (24%) at Test 3, and 8 (32%) at Tests 4, 5, and 6. Thirteen respirator users (52%) achieved ≥100 throughout the fit testing, so 12 had at least one failure at either Tests 2-6. Five of the 12 subjects with at least one failure showed persistent failures on all subsequent donnings. Six subjects out of 12 (50%) who failed a fit test achieved an overall fit factor >100 at a subsequent test. There was a significant difference between the median first and sixth overall fit factors (195 versus 150; P = 0.0271), but not between the second and sixth (161 versus 150; P = 0.3584). Men and women had similar overall fit factors, but infrequent users had larger average overall fit factors than frequent users after all six donnings. Forty-eight percent of study subjects failed at least one fit test after re-donning an N95 FFR. The fit test data suggest that donning practices probably accounted for the fit test failures. The 50% of subjects who produced overall fit factors ≥100 after a test of <100 supports this contention.

Aerosol emission and superemission during human speech increase with voice loudness

Mechanistic hypotheses about airborne infectious disease transmission have traditionally emphasized the role of coughing and sneezing, which are dramatic expiratory events that yield both easily visible droplets and large quantities of particles too small to see by eye. Nonetheless, it has long been known that normal speech also yields large quantities of particles that are too small to see by eye, but are large enough to carry a variety of communicable respiratory pathogens. Here we show that the rate of particle emission during normal human speech is positively correlated with the loudness (amplitude) of vocalization, ranging from approximately 1 to 50 particles per second (0.06 to 3 particles per cm3) for low to high amplitudes, regardless of the language spoken (English, Spanish, Mandarin, or Arabic). Furthermore, a small fraction of individuals behaves as “speech superemitters,” consistently releasing an order of magnitude more particles than their peers. Our data demonstrate that the phenomenon of speech superemission cannot be fully explained either by the phonic structures or the amplitude of the speech. These results suggest that other unknown physiological factors, varying dramatically among individuals, could affect the probability of respiratory infectious disease transmission, and also help explain the existence of superspreaders who are disproportionately responsible for outbreaks of airborne infectious disease.

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.

Development and Implementation of Behavioral Intervention Team Model at Johns Hopkins Hospital: Preliminary Analysis of Effectiveness

The adequate fit of an N95 respirator is important for health care workers to reduce the transmission of airborne infectious diseases in the clinical setting. This study aimed to evaluate whether adequately sealed N95 respirators may provide consistent protection for the wearer while performing nursing procedures.Participants were a group of nursing students (N = 120). The best fitting respirator for these participants was identified from the 3 common models, 1860, 1860S, and 1870+ (3M), using the quantitative fit test (QNFT) method. Participants performed nursing procedures for 10-minute periods while wearing a backpack containing the portable aerosol spectrometers throughout the assessment to detect air particles inside the respirator.The average fit factor of the best fitting respirator worn by the participants dropped significantly after nursing procedures (184.85 vs 134.71) as detected by the QNFT. In addition, significant differences in particle concentration of different sizes (>0.3, >0.4, >1.0, and >4.0 µm) inside the respirator were detected by the portable aerosol spectrometers before, during, and after nursing procedures.Body movements during nursing procedures may increase the risk of face seal leakage. Further research, including the development of prototype devices for better respirator fit, is necessary to improve respiratory protection of users.

Reliability of N95 respirators for respiratory protection before, during, and after nursing procedures

The adequate fit of an N95 respirator is important for health care workers to reduce the transmission of airborne infectious diseases in the clinical setting. This study aimed to evaluate whether adequately sealed N95 respirators may provide consistent protection for the wearer while performing nursing procedures. Participants were a group of nursing students (N = 120). The best fitting respirator for these participants was identified from the 3 common models, 1860, 1860S, and 1870+ (3M), using the quantitative fit test (QNFT) method. Participants performed nursing procedures for 10-minute periods while wearing a backpack containing the portable aerosol spectrometers throughout the assessment to detect air particles inside the respirator. The average fit factor of the best fitting respirator worn by the participants dropped significantly after nursing procedures (184.85 vs 134.71) as detected by the QNFT. In addition, significant differences in particle concentration of different sizes (>0.3, >0.4, >1.0, and >4.0 µm) inside the respirator were detected by the portable aerosol spectrometers before, during, and after nursing procedures. Body movements during nursing procedures may increase the risk of face seal leakage. Further research, including the development of prototype devices for better respirator fit, is necessary to improve respiratory protection of users.

Computational modeling of time resolved exposure level analysis of a heated breathing manikin with rotation in a room

With people spending most of their time indoor, the air quality in indoor environment has become a subject of serious concern. Of particular interest is the mitigation of transmission of airborne infectious diseases in indoor facilities. The airflow pattern in indoor environment is affected by the ventilation system, thermal plume around human bodies, human respiration, human walking and other activities. In the present study, the effects of thermal plume, respiration and motion of the body on the indoor air quality in a ventilated cubicle were investigated using a computational modeling approach. Attention was given to the transport and fate of particulate pollutant in a ventilated room in the presence of a heated, breathing and rotating manikin. The cases of displacement and mixing ventilations were studied. In particular, the concentration of pollutant in the breathing zone of the manikin under various conditions was evaluated. The simulation results indicated that the rotation of the manikin significantly distorted the thermal plume of the body and the associated transport of particulates. Furthermore, the rotation decreased the concentration of particles in the breathing zone of the manikin. It was also found that the thermal plume generated by the body was distorted by the airflow of the mixing ventilation system, while there is little if any distortion by the displacement ventilation system.

A qualitative exploration of social contact patterns relevant to airborne infectious diseases in northwest Bangladesh.

In South Asia, the burden of infectious diseases is high. Socioeconomically and culturally-defined social interaction patterns are considered to be an important determinant in the spread of diseases that are transmitted through person-to-person contact. Understanding of the contact patterns in this region can be helpful to develop more effective control measures. Focus group discussions were used in exploring social contact patterns in northwest Bangladesh. The patterns were assessed for perceived relevance to the spread of airborne infectious diseases, with special focus on diseases, like leprosy and tuberculosis, in which the role of social determinants is well-recognized. Highly-relevant social contact patterns inside the home and the neighbourhood, across age and sex groups, were reported in all group discussions. Outside the home, women and girls reported relevant contacts limited to the close neighbourhood while men mentioned high relevant contacts beyond. This implies that, in theory, infectious diseases can easily be transmitted across age and sex groups in and around the home. Adult men might play a role in the transmission of airborne infectious diseases from outside this confined area since only this group reported highly-relevant social contacts beyond the home. This concept needs further exploration but control programmes in the South Asian region could benefit from considering differences in social contact patterns by gender for risk assessments and planning of preventive interventions.

Simplified models for exhaled airflow from a cough with the mouth covered

Covering a cough can be useful in reducing the transmission of airborne infectious diseases. However, no simple method is available in the literature for predicting the exhaled airflow from a cough with the mouth covered. This investigation used smoke to visualize the airflow exhaled by 16 human subjects. Their mouths were covered by a tissue, a cupped hand, a fist, and an elbow with and without a sleeve. This study then developed simplified models for predicting the airflow on the basis of the smoke visualization data. In addition, this investigation performed numerical simulations to assess the influence of mouth coverings on the receptor's exposure to exhaled particles. It was found that covering a cough with a tissue, a cupped hand, or an elbow can significantly reduce the horizontal velocity and cause the particles to move upward with the thermal plumes generated by a human body. In contrast with an uncovered cough, a covered cough or a cough with the head turned away may prevent direct exposure. This study developed simplified models for predicting the exhaled airflow from a cough with the mouth covered. The proposed models can easily be used to investigate the risk of transmission of airborne infectious diseases in enclosed environments.

Adequacy of air change rate as the sole indicator of an air distribution system's effectiveness to mitigate airborne infectious disease transmission caused by a cough release in the room with overhead mixing ventilation: A case study

In indoor environments where airborne infectious disease transmission is of concern, air change rate is conventionally used as the sole indicator of air delivery system performance. This indicator, based on the total volume dilution reasoning, suggests that increase of the supply flow rate will reduce risk of airborne infectious disease transmission. Results obtained from recent studies on cough release conducted in the field environmental chamber (FEC) at the National University of Singapore indicate that increase of supply flow rate may cause increase in the airborne infection risk transmission for several positions of the cough source and the susceptible person in relation to the supply and return air grills. Particle image velocimetry (PIV) was used for airflow field investigation, while a Grimm 1.108 aerosol counter was used to measure droplet concentration in the FEC. Results from this study imply that a local airflow pattern is an important factor influencing dispersion of cough droplets and consequential exposure. It is demonstrated that increase in supply flow rate can lead to an increase in exposure under certain circumstances. This further implies that air change rate should not be used as the sole indicator of the air delivery system's ability to reduce exposure to airborne infectious droplets.

Predicting transient particle transport in enclosed environments with the combined computational fluid dynamics and Markov chain method

To quickly obtain information about airborne infectious disease transmission in enclosed environments is critical in reducing the infection risk to the occupants. This study developed a combined computational fluid dynamics (CFD) and Markov chain method for quickly predicting transient particle transport in enclosed environments. The method first calculated a transition probability matrix using CFD simulations. Next, the Markov chain technique was applied to calculate the transient particle concentration distributions. This investigation used three cases, particle transport in an isothermal clean room, an office with an underfloor air distribution system, and the first-class cabin of an MD-82 airliner, to validate the combined CFD and Markov chain method. The general trends of the particle concentrations vs. time predicted by the Markov chain method agreed with the CFD simulations for these cases. The proposed Markov chain method can provide faster-than-real-time information about particle transport in enclosed environments. Furthermore, for a fixed airflow field, when the source location is changed, the Markov chain method can be used to avoid recalculation of the particle transport equation and thus reduce computing costs.

Aerobiology and its role in the transmission of infectious diseases.

Aerobiology plays a fundamental role in the transmission of infectious diseases. As infectious disease and infection control practitioners continue employing contemporary techniques (e.g., computational fluid dynamics to study particle flow, polymerase chain reaction methodologies to quantify particle concentrations in various settings, and epidemiology to track the spread of disease), the central variables affecting the airborne transmission of pathogens are becoming better known. This paper reviews many of these aerobiological variables (e.g., particle size, particle type, the duration that particles can remain airborne, the distance that particles can travel, and meteorological and environmental factors), as well as the common origins of these infectious particles. We then review several real-world settings with known difficulties controlling the airborne transmission of infectious particles (e.g., office buildings, healthcare facilities, and commercial airplanes), while detailing the respective measures each of these industries is undertaking in its effort to ameliorate the transmission of airborne infectious diseases.

Evidence for airborne infectious disease transmission in public ground transport – a literature review

While guidelines on contact tracing (CT) after exposure to certain infectious pathogens during air travel exist, no guidance documents are available on CT in response to potential exposure on public ground transport. We reviewed scientific and non-scientific literature on transmission of airborne pathogens in public ground transport and on factors potentially influencing transmission. We identified 32 relevant publications (15 scientific and 17 non-scientific). Most of the selected studies dealt with transmission of tuberculosis. However, the relation between travel duration, proximity to the index case and environmental factors, such as ventilation, on disease transmission in public ground transport is poorly understood. Considering the difficulty and probably limited effectiveness of CT in ground transport, our results suggest that only exceptional circumstances would justify CT. This contrasts with the high level of attention CT in air travel seems to receive in international regulations and recommendations. We question whether the indication for CT should be revisited after a risk–benefit assessment that takes into account exposure in both ground and air transport.

Assessment of the mixing air delivery system ability to protect occupants from the airborne infectious disease transmission using Wells–Riley approach

Assessment of a mixing air delivery system's ability to protect occupants from airborne infectious disease transmission using the Wells–Riley equation modified for unsteady heterogenic conditions was performed in this study. Experiments were performed in a field environmental chamber equipped with mixing ventilation, while the cough was simulated using a cough machine. Results show that increase of supply flow rate up to 3 ACH rapidly reduces cough-induced inhalation fraction, but an increase above 6 ACH causes minor changes. When the infectiousness of the index case is relatively low, changes in the supply flow rate will not cause any change in the protective effectiveness of the air delivery system, while for the index case of relatively moderate infectiousness, an increase in supply flow rate up to 6 ACH will improve the protective effectivenes. For the index case of high infectiousness, an increase of supply flow rate will reduce the number of secondary cases for the 8-h exposure period. Maximum protective effectiveness depends only on ability of the system to reduce the exposure, but the index case infectiousness at which this is achieved will depend on the exposure period and exposure reduction.

A one-dimensional analytical model for airborne contaminant transport in airliner cabins

Quick information on airborne infectious disease transmission in airliner cabins is essential to reduce the risk of infection of passengers and crew members. This investigation proposed a one-dimensional analytical model that can predict the longitudinal transmission of airborne contaminants or disease viruses inside an airliner cabin. The model considered both diffusive and convective transport of contaminants in the longitudinal direction of the cabin but assumed complete mixing of contaminants in the cabin cross-section. The effect of recirculation of the cabin air and efficiency of the high-efficiency particulate air (HEPA) filters is also considered in the model. The analytical solution for the one-dimensional contaminant transport model is obtained by using the principle of superposition and the method of separation of variables. The analytical solutions agree well with the computational fluid dynamics (CFD) results. The coupling of a CFD model with the one-dimensional analytical model could capture the impact of local airflow on contaminant transport. This analytical model has been used for analyzing contaminant transport in a 30-row all-economy-class airliner cabin with minimal computing effort. The paper presents a new one-dimensional analytical model that can provide quick information on global airborne contaminant transmissions in airliner cabins for effective response plans. The model can be used to study the effects of air exchange rates, recirculation, efficiency of the high-efficiency particulate air (HEPA) filters and longitudinal airflow on airborne contaminant transport in airliner cabins with minimal computing effort.

High risk of Mycobacterium tuberculosis infection during the Hajj pilgrimage

Annually more than 2 million pilgrims from all over the world attend the Hajj in Saudi Arabia. Overcrowding during this pilgrimage leads to a high risk of transmission of airborne infectious diseases. Tuberculosis (TB) is common among hospitalized pilgrims, but the overall risk of acquiring Mycobacterium tuberculosis infection during this pilgrimage is not known. We conducted a prospective study to assess the risk of M. tuberculosis infection among Hajj pilgrims. We measured the immune response to TB antigens using a whole-blood assay (QuantiFERON TB assay) prior to departure and 3 months after return from the Hajj pilgrimage. Of 357 paired assays, 149 pilgrims were negative prior to the Hajj and 15 (10%) of these had a significant rise in immune response to TB antigens. Pilgrims may be at high risk of acquiring M. tuberculosis infection during the Hajj. This has significant public health implications for TB control in countries with large Muslim populations.

Predicting the Ultraviolet Radiation Distribution in a Room with Multilouvered Germicidal Fixtures

Irradiating the upper part of a room with 254-nm ultraviolet (UV) radiation from a low-pressure mercury discharge lamp has the potential to be a relatively inexpensive method to reduce transmission of airborne infectious diseases such as tuberculosis. To protect occupants in the lower part of a room from radiation, multilouvered UV germicidal fixtures producing a horizontal, collimated beam are often used, particularly in rooms having a normal ceiling height. Knowledge of the fixture's emission characteristics and the airflow field are needed to estimate the UV dose to airborne microorganisms and assess the fixture's overall effectiveness in controlling disease transmission. In this article, a model is developed to predict the UV fluence rate at any location in the upper room for ceiling-mounted, multilouvered, pendant-type fixtures, which provide 360-degree emission in the horizontal plane. The model also predicts total UV power emitted by the fixture, which is the best single-number effectiveness index for comparing multilouvered UV germicidal fixtures. Model predictions compared favorably with laboratory and field measurements.

Characterization of infectious aerosols in health care facilities: An aid to effective engineering controls and preventive strategies

Assessment of strategies for engineering controls for the prevention of airborne infectious disease transmission to patients and to health care and related workers requires consideration of the factors relevant to aerosol characterization. These factors include aerosol generation, particle sizes and concentrations, organism viability, infectivity and virulence, airflow and climate, and environmental sampling and analysis. The major focus on attention to engineering controls comes from recent increases in tuberculosis, particularly the multidrug-resistant varieties in the general hospital population, the severely immunocompromised, and those in at-risk and confined environments such as prisons, long-term care facilities, and shelters for the homeless. Many workers are in close contact with persons who have active, undiagnosed, or insufficiently treated tuberculosis. Additionally, patients and health care workers may be exposed to a variety of pathogenic human viruses, opportunistic fungi, and bacteria. This report therefore focuses on the nature of infectious aerosol transmission in an attempt to determine which factors can be systematically addressed to result in proven, applied engineering approaches to the control of infectious aerosols in hospital and health care facility environments. The infectious aerosols of consideration are those that are generated as particles of respirable size by both human and environmental sources and that have the capability of remaining viable and airborne for extended periods in the indoor environment. This definition precludes skin and mucous membrane exposures occurring from splashes (rather than true aerosols) of blood or body fluids containing infectious disease agents. There are no epidemiologic or laboratory studies documenting the transmission of bloodborne virus by way of aerosols. (AJIC Am J Infect Control 1998;26:453-64)

Air Volume Migration from Negative Pressure Isolation Rooms during Entry/Exit

Abstract Negative-pressure isolation rooms (NPIRs) are used to isolate patients who have a suspected or known airborne infectious disease from the general hospital environment. When a person passes through an NPIR doorway, there exists an exchange of air between the isolation room and the area beyond its door. In a recent study, National Institute for Occupational Safety and Health researchers used sulfur hexafluoride tracer gas to examine the magnitude of air volume migration (AVM) as a function of several independent variables. A small cart carried a mannequin through a doorway separating a laboratory NPIR and a sulfur hexafluoride measurement chamber. The configuration provided simulated entry/exit of a healthcare worker through the doorway. Upon completion of experiments using a swinging door (including various cycle speeds for the door), a sliding door was installed and the experiments were repeated. In all cases examined, air flow rate differential between the air supplied to, and exhausted from, the NPIR was the only statistically significant factor in determining the level of AVM. Across the range of flow differentials examined (50 to 220 ft3/min), AVM ranged from 35 to 65 ft3. This range of AVM remained statistically unchanged regardless of door type, operating speed of the door, or entry to or exit from the NPIR. (Although entry/exit did significantly increase AVM, travel direction, whether entering or exiting the NPIR, did not.) By knowing the level of AVM during entry/exit through a doorway—a cause of airborne contaminant migration through a facility—a more complete assessment of the risk of transmission of an airborne infectious disease is made possible. This study shows that an anteroom or buffer zone outside the contaminated area's doorway will offer a degree of containment during entry/exit not otherwise obtainable. While this study concerned itself primarily with the engineering control of the transmission of airborne infectious diseases provided by ventilation systems, the results are applicable to any environment where a clean area is separated from a less clean area by a doorway. Hayden, II, C.S.; Johnston, O.E.; Hughes, R.T.; Jensen, P.A.: Air Volume Migration from Negative Pressure Isolation Rooms During Entry/Exit.