Airborne Infection Research Articles

Integrated infection and crowd behaviour model for COVID-19 infection risk assessment onboard large passenger vessels

The development of the global COVID-19 pandemic from 2020 onward has had significant impact on the world and specifically the maritime industry. Striking examples were COVID-19 outbreaks onboard the Diamond Princess cruise vessel and the U.S.S. Theodore Roosevelt aircraft carrier at the start of the pandemic. Contagious disease management onboard large passenger ships remains a complex issue, amplified by the international character of the industry, confined environment and shared facilities. This paper therefore presents an integrated infection and crowd behavior model used to calculate agent-specific infection risk, incorporating guest and crew circulation through a passenger ship layout. The integrated model is used to investigate the effect of ship layout design, capacity reduction and mask wearing on COVID-19 airborne infection risk onboard large passenger vessels.

A fieldable process for sensitive detection of airborne viruses via electrophoresis-based RNA enrichment

Sensitive on-site virus detection is a requirement for timely action against the spread of airborne infection since ultra-low in-air viral concentrations can readily infect individuals when inhaled. Here, we consider a fieldable biosensing process that incorporates a fast RNA enrichment step in order to concentrate viral RNA in a small volume prior to RT-qPCR. The enrichment approach uses electrophoresis in an RT-qPCR-compatible buffer, and allows for concentration of RNA by nearly 5-fold within only 10 min. In order to place this performance into context, we analyzed the minimum detectable concentration of a low-cost, fieldable, biosensing process that uses electrostatic precipitation for air sampling, heating for viral RNA extraction, and then RNA enrichment, followed by RT-qPCR. With enrichment, we estimated an in-air concentration of 5,654 genome copies (gc)/m3 with a 100% detection rate and an in-air concentration of 4,221 gc/m3 with a 78.6% detection rate. Given that the concentrations of common viruses, such as influenza and SARS-CoV-2, in several indoor spaces are between 5,800 and 37,000 gc/m3, we conclude that enrichment allows a detection that is sufficiently sensitive for practical applications.

Experimental study on enhancing electrostatic charging of nonwoven filter media through novel electrode configurations

The COVID-19 pandemic has underscored the urgent need for efficient particle filtration to tackle public health challenges. This study compares the electrostatic charging capabilities of two types of electrodes: conventional Metal Lamellar Electrodes (MLE) and Modified Lamellar Plate Electrodes (MLPE) with PMMA insulation, in their role of charging nonwoven polypropylene filter media. Experimental analysis unequivocally demonstrates the superiority of MLPE in promoting effective electrostatic charge, as influenced by applied high voltage and inter-electrode distance, resulting in a significant enhancement in fine particle filtration. Numerical simulations of the electric field conducted using the COMSOL software and employing the Finite Element Method (FEM) validate these findings. FEM discretizes the domain into small finite elements and applies Laplace's equation in charge-free regions, providing a comprehensive understanding of the behavior of dual-electrode corona discharge systems. These simulations indicate higher field intensities for MLPE compared to MLE.By integrating experimental and numerical analyses, this study sheds light on the potential benefits of MLPE for air filtration systems, offering a noteworthy advancement in the control of airborne infections and reduction of environmental health risks. This research lays the groundwork for the development of more efficient and durable filtration systems, meeting the increasing demands for public health protection.The findings of this study suggest that the adoption of MLPE could significantly contribute to improving indoor air quality and mitigating the transmission of respiratory diseases. MLPE may also find utility in industrial filtration and air purification in sensitive work environments. Ultimately, this research sets the stage for the development of more efficient and sustainable filtration systems, addressing the growing needs for public health protection.

Second Time's the Charm? Assessing the Sensitivity and Yield of Inpatient Diagnostic Algorithms for Pulmonary Tuberculosis in a Low-Prevalence Setting.

For persons with suspected pulmonary tuberculosis, the guidelines of the Centers for Disease Control and Prevention recommend collecting 3 respiratory specimens 8 to 24 hours apart for acid-fast bacilli (AFB) smear and culture, in addition to 1 nucleic acid amplification test (NAAT). However, data supporting this approach are limited. Our objective was to estimate the performance of 1, 2, or 3 AFB smears with or without NAATs to detect pulmonary tuberculosis in a low-prevalence setting. We conducted a retrospective study of hospitalized persons at 8 Massachusetts acute care facilities who underwent mycobacterial culture on 1 or more respiratory specimens between July 2016 and December 2022. We evaluated percentage positivity and yield on serial AFB smears and NAATs among people with growth of Mycobacterium tuberculosis on mycobacterial cultures. Among 104 participants with culture-confirmed pulmonary tuberculosis, the first AFB smear was positive in 41 cases (39%). A second AFB smear was positive in 11 (22%) of the 49 cases in which it was performed. No third AFB smears were positive following 2 initial negative smears. Of 52 smear-negative cases, 36 had a NAAT performed, leading to 23 additional diagnoses. Overall sensitivity to detect tuberculosis prior to culture positivity was higher in any strategy involving 1 or 2 NAATs (74%-79%), even without AFB smears, as compared with 3 smears alone (60%). Tuberculosis diagnostic testing with 2 AFB smears offered the same yield as 3 AFB smears while potentially reducing laboratory burden and duration of airborne infection isolation. Use of 1 or 2 NAATs increased sensitivity to detect culture-positive pulmonary tuberculosis when added to AFB smear-based diagnostic testing alone.

The Role of Human Mobility Flow in the Region-to-Region Spread of Respiratory Syncytial Virus Infection among Infants: An Infographic Analysis.

The region-to-region spread of human infectious diseases is considered to be dependent on the human mobility flow (HMF). However, it has been hard to obtain the evidence for this. Since the onset of the coronavirus disease 2019 (COVID-19) pandemic in Japan 2020, the government has enforced countermeasures against COVID-19 nationwide, namely the restriction of personal travelling, universal masking, and hand hygiene. As a result, the spread of acute respiratory infections had been effectively controlled. However, COVID-19 as well as pediatric respiratory syncytial virus (RSV) infections were not well-controlled. The region-to-region spread of pediatric RSV infections in 2020-2021 was recognizable unlike those in 2018 and 2019. In this study, we investigated the correlation between the trend of regional reports of the pediatric RSV infections and the HMF based on cellular phone signal data. Upon closer examination of both epidemiological trend and HMF data, the spread of pediatric RSV infection from one region to another was logically explained by HMF, which would serve as the evidence of the dependence of regional transmission on HMF. This is the first solid evidence where this correlation has been clearly observed for the common respiratory infections. While social implementation of infection control measures has successfully suppressed the droplet-mediated respiratory infections, such as influenza, but not the airborne infections, it was suggested that the aerosol transmission and adult asymptomatic carrier were involved in the transmission of RSV akin to COVID-19.

The ouroboros of autoimmunity.

Human autoimmunity against elements conferring protective immunity can be symbolized by the 'ouroboros', a snake eating its own tail. Underlying infection is autoimmunity against three immunological targets: neutrophils, complement and cytokines. Autoantibodies against neutrophils can cause peripheral neutropenia underlying mild pyogenic bacterial infections. The pathogenic contribution of autoantibodies against molecules of the complement system is often unclear, but autoantibodies specific for C3 convertase can enhance its activity, lowering complement levels and underlying severe bacterial infections. Autoantibodies neutralizing granulocyte-macrophage colony-stimulating factor impair alveolar macrophages, thereby underlying pulmonary proteinosis and airborne infections, type I interferon viral diseases, type II interferon intra-macrophagic infections, interleukin-6 pyogenic bacterial diseases and interleukin-17A/F mucocutaneous candidiasis. Each of these five cytokine autoantibodies underlies a specific range of infectious diseases, phenocopying infections that occur in patients with the corresponding inborn errors. In this Review, we analyze this ouroboros of immunity against immunity and posit that it should be considered as a factor in patients with unexplained infection.

Knowledge and Practices of Airborne Infection Control at the Household Level among Pulmonary Tuberculosis Patients Attending a Tertiary Care Teaching Hospital in Central Karnataka, India

Abstract Background: Airborne transmission of tuberculosis (TB) is a major route of spread. Household contacts of TB patients are at high risk of infection. However, there is limited evidence on airborne infection control knowledge and practices among TB patients in India. This study was done to assess the knowledge and practices related to airborne infection control among pulmonary TB (PTB) patients at the household level and determine associated factors. Subjects and Methods: A cross-sectional study was conducted among 157 smear-positive PTB patients at a tertiary care hospital in Karnataka, India, using a pretested questionnaire. Knowledge and self-reported practices regarding airborne precautions were assessed. Bivariate analysis was done to determine associated factors. P <0.005 was considered significant. Results: Major gaps were found in knowledge about ventilation (50.3%), avoiding visitors (39.5%), and sputum disposal (33.8%). Suboptimal practices were reported for using tissues (19%), handwashing (25%), ventilation (66%), sputum handling (54%), and waste disposal (30%). Good knowledge was associated with younger age, higher education, Hindu religion, family history of TB, intensive phase treatment, and presence of symptoms (P < 0.05). Participants with good knowledge had significantly better preventive practices (P < 0.00001). Conclusion: Tailored education on airborne precautions focusing on identified knowledge gaps and risky practices can help improve the adoption of infection control measures among TB patients at the household level. A multifaceted approach is required to translate improved awareness into optimal preventive behaviors.

Airborne Infection Control measures among Government and Private Health Facilities in a hilly district of North India

Introduction: Guidelines for Airborne Infection Control in Health Care Settings were published in the 2010 to reduce Airborne Infections in health service providers and visitors to health facilities. Objectives: To evaluate healthcare facilities regarding implementation of Guidelines for Airborne Infection Control in Health Care Settings. Methods: An analytic, cross- sectional, health care facility-based study in the district Solan of Himachal Pradesh. A total 53 health care facilities from both public and private sectors were assessed and compared. Results: The implementation of these guidelines was unsatisfactory. Government health care facilities were better implementing the guidelines, compared to the private sector. Conclusion: The guidelines are over a decade old and implementation is not optimal. Efforts and emphasis are required to be put into implementation of these guidelines in health care facilities. An update of policy with stringent penalties are advocated for better compliance in the private sector.

Conversion of a regular patient room to negative pressure at Ancona university hospital (Italy). A combined experimental and numerical investigation

Negative pressure isolation rooms are employed to prevent the spread of infectious diseases to surrounding spaces. This study reports a combined experimental and numerical analysis aimed at reliably assessing the performance of hospital ventilation systems and effectively reducing the risk of airborne infections. The study appraises the enhancement of the safety conditions by retrofitting an existing, positive pressure room ventilation system with a negative pressure and recirculation one. The assessment consisted in experimental measurements of airborne particle concentration and Computational Fluid Dynamics (CFD) simulations with Lagrangian particle tracking of respiratory droplets. The ventilation performance improvement was quantified in terms of recovery rate, contaminant removal effectiveness, particle transfer toward adjacent spaces and probability of infection.Two experimental campaigns were carried out: an ISO standard recovery assessment and a test in real operational conditions. The negative pressure configuration significantly improved the safety inside the patient ward: the recovery rate for droplets with diameter larger than 5 μm increased by a factor three, and the contaminant removal effectiveness after 15 min increased from 45% to 81%. The numerical model for Computational Fluid Dynamics simulation was successfully validated, confirming the ability of the approach to reproduce the undergoing Physics. The negative pressure design eliminated the particle transmission to surrounding spaces, while 2.5% of the emitted respiratory droplets escaped the room in the original existing scenario. The probability of infection after 15 min exposure was reduced by a factor three and peak values reaching 15% were limited to the immediate vicinity of the patients.

Reducing the contaminant dispersion and infection risks in the train cabins by adjusting the inlet turbulence intensity: A study based on turbulence simulation

Existing studies on ventilation in closed spaces mainly considered the average inlet velocity and ignored the influence of inlet turbulent fluctuation. However, the variation in inlet turbulence intensity (TI) is considerable and significantly affects the dispersion of contaminants. This study conducts numerical simulations verified by experiments to investigate the effect of the inlet TI on train contaminants dispersion and analyze infection probability variation. Firstly, the unsteady Reynolds-averaged Navier-Stokes (URANS) method and improved delayed detached eddy simulation (IDDES) method are compared in simulating the internal airflow characteristics based on the on-site measurement. The results indicate that the latter dominates in capturing airflow pulsations more than the former, although the mean airflow results obtained from both methods agree well with experimental results. Furthermore, the IDDES method is employed to investigate the effect of the inlet TI on contaminant dispersion, and the infection risks are also assessed using the improved probability model. The results show that, with the increase of TI from 5 % to 30 %, the contaminant removal grows considerably, with the removal index rising from 0.23 to 1.86. The increased TI leads to the overall and local infection risks of occupants descending significantly, wherein the former decreases from 1.53 % to 0.88 % with a reduction rate of 42 %, and the latter drops from 3.30 % to 2.16 % with a mitigation rate of 35 %. The findings can serve as solid guidelines for numerical method selection in accurately capturing the indoor dynamic airflow distribution and for the ventilation parameters design regarding TI inside trains to mitigate the airborne infection risk.

Performance investigation of a novel positively or negatively pressurized operating room for infection control

Operating rooms are often positively pressurized and maintained at a higher pressure than adjacent areas, preventing contaminated air from entering the sterile surgical environment. However, the COVID-19 outbreak has necessitated the construction of negatively pressurized operating rooms for contagious patients, preventing contaminated air from escaping into adjacent spaces. Therefore, this study developed a heating, ventilation, and air-conditioning (HVAC) system that can have a dual function pressurization, positively or negatively pressurized. High-efficiency particulate air (HEPA) filters were used for filtration. Then, a variable-speed driven (VSD) HVAC system modulates the pressure in response to environmental conditions when changing the pressure from positive to negative or while the door opens. At the same time, the air change rate (ACR) for dilution was implemented through the separated HVAC systems control schemes. Field measurements were performed to validate the results of a computational fluid dynamics (CFD) simulation, which was conducted to compare air particle distributions in a positively and negatively pressurized operating room and the effects of air curtains. The results showed that the positive pressurized operating room has a better airflow pattern and dilutes contaminants faster. In contrast, the negative pressurized system is the best solution for reducing the chance of airborne infection, particularly for contagious patients. Furthermore, utilizing air curtains can provide a better barrier against airborne contaminants, increasing the efficiency of contaminant control measures. The ventilation efficiency could be increased by approximately 10 % by applying an air curtain with a velocity of 0.5 m/s under both types of pressurization.

Effects of surface-attached durations, nutrients, and relative humidity on the resuspension of bacteria during human walking

Resuspension caused by human walking activities is an important source of indoor bioaerosols and has been associated with health effects such as allergies and asthma. However, it is unknown whether inhalation of resuspended bioaerosols is an important exposure pathway for airborne infection. Also, crucial factors influencing the resuspension of settled microbes have not been quantified. In this study, we experimentally investigated the resuspension of culturable bacteria from human-stepping on polyvinyl chloride (PVC) flooring under different conditions. We determined the bacterial resuspension emission factor (ER), a normalized resuspension parameter for the ratio of resuspended mass in the air to the mass of settled particles, for two common bacteria, Escherichia coli and Salmonella enterica. The investigation involved varying factors such as microbial surface-attached durations (0, 1, 2, and 3 days), the absence or presence of nutrients on flooring surfaces, and changes in relative humidity (RH) (35%, 65%, and 85%). The results showed that, in the absence of nutrients, the highest ER values for E. coli and S. enterica were 3.8 × 10−5 ± 5.2 × 10−6 and 5.3 × 10−5 ± 6.0 × 10−6, respectively, associated with surface-attached duration of 0 days. As the surface-attached duration increased from 0 to 3 days, ER values decreased by 92% and 84% for E. coli and S. enterica, respectively. In addition, we observed that ER values decreased with the increasing RH, which is consistent with particle adhesion theory. This research offers valuable insights into microbial resuspension during human walking activities and holds the potential for assisting in the assessment and estimation of risks related to human exposure to bioaerosols.

An experimental study on airborne transmission in a meeting room with different air distribution methods

Aerosols are one of the major sources of cross-infection. The main purpose of this study is to analyze the effects of heat gain, airflow rate, air distribution, and the location of an infector on the airborne transmission and infection probability in a meeting room. In a six-person meeting room the droplet nuclei of an infected person were simulated with tracer gas (SF6) generated by a thermal breathing manikin. An overhead perforated duct (OPD) and low velocity unit (LVU) were used and their performance was compared. With OPD, the average contaminant removal efficiency in the breathing zone was quite uniformly between 0.9 and 1.1. With LVU, the average contaminant removal efficiency varied greatly between 0.2 and 10.1. The airborne generation was assumed to be 5 quantum/h by an infected person. The infection probability for every exposed person was found to be quite uniform with OPD, 1.4 % with a heat gain and air flow rate of 38 W/m2 and 61 l/s and 0.9 % with a heat gain and air flow rate of 60 W/m2 and 116 l/s after 3 hours’ exposure. However, variation of the infection probability with LVU was significant and the highest risk reached 4 %. The infection probability was lower if the exposed person was farther from the infector, or in the case of OPD if the infector was near the exhaust. With LVU, the infection probability depended on the airflow rate and the relative distance between the supply unit and the exposed person.

Assessing Tuberculosis and Risk Factors: Population Study in Rivers State, Nigeria's Niger Delta Region, Nigeria

Mycobacterium tuberculosis (MTB), an infectious airborne bacterium primarily impacting the lungs and instigating a chronic inflammatory response, persists as an enduring menace. This study aims to evaluate the interplay between MTB infection and associated risk factors in Rivers State, Nigeria. The study involved 392 participants from three local government areas (LGAs): Eleme, Obio/Akpor, and PHALGA. Data collection involved a structured questionnaire covering socio-demographics variables and associated risk factors. A stratified random sampling method was employed. Statistical analysis, including descriptive statistics and Spearman's correlation coefficient, was performed using SPSS version 25. Correlation analysis of socio-demographic variables revealed no significant associations with MTB, as indicated by non-significant p-values of (p=0.27), (p=0.83), (p=0.42), (p=0.35), (p=0.49), (p=0.28) for age, sex, education, occupation, marital status and geographical area respectively. However, significant positive weak correlations emerged between MTB infection and cough (p=0.00), hepatitis (p=0.01), coughing blood (p=0.00), and fever (p=0.00). Conversely, family TB history (p=0.93), cough lasting 2 weeks (p=0.84), weight loss (p=0.19), contact with a person who has been coughing for 2 weeks (p=0.93), and alcohol consumption (p=0.55) did not show significant associations. While demographic characteristics alone may not be strong predictors of MTB infection, this study highlights the complex interplay between various risk factors Addressing these risk factors through targeted interventions and raising awareness can contribute to reducing the TB burden in Rivers State and the Niger Delta region.

A quanta-independent approach for the assessment of strategies to reduce the risk of airborne infection

The Wells-Riley model is extensively used for retrospective and prospective modelling of the risk of airborne transmission of infection in indoor spaces. It is also used when examining the efficacy of various removal and deactivation methods for airborne infectious aerosols in the indoor environment, which is crucial when selecting the most effective infection control technologies. The problem is that the large variation in viral load between individuals makes the Wells-Riley model output very sensitive to the input parameters and may yield a flawed prediction of risk. The absolute infection risk estimated with this model can range from nearly 0 % to 100 % depending on the viral load, even when all other factors, such as removal mechanisms and room geometry, remain unchanged. We therefore propose a novel method that removes this sensitivity to viral load. We define a quanta-independent maximum absolute before-after difference in infection risk that is independent of quanta factors like viral load, physical activity, or the dose-response relationships. The input data needed for a non-steady-state calculation are just the removal rates, room volume, and occupancy duration. Under steady-state conditions the approach provides an elegant solution that is only dependent on removal mechanisms before and after applying infection control measures. We applied this method to compare the impact of relative humidity, ventilation rate and its effectiveness, filtering efficiency, and the use of ultraviolet germicidal irradiation on the infection risk. The results demonstrate that the method provides a comprehensive understanding of the impact of infection control strategies on the risk of airborne infection, enabling rational decisions to be made regarding the most effective strategies in a specific context. The proposed method thus provides a practical tool for mitigation of airborne infection risk.

Analysis of a Large Severe Acute Respiratory Syndrome Coronavirus 2 (Alpha) Outbreak in a Catalan Prison Using Conventional and Genomic Epidemiology.

Enforcing strict protocols that prevent transmission of airborne infections in prisons is challenging. We examine a large severe acute respiratory syndrome coronavirus 2 outbreak in a Catalan penitentiary center in February-April 2021, prior to vaccination deployment. The aim was to describe the evolution of the outbreak using classical and genomic epidemiology and the containment strategy applied. The outbreak was initially detected in 1 module but spread to 4, infecting 7 staff members and 140 incarcerated individuals, 6 of whom were hospitalized (4.4%). Genomic analysis confirmed a single origin (B.1.1.7). Contact tracing identified transmission vectors between modules and prevented further viral spread. In future similar scenarios, the control strategy described here may help limit transmission of airborne infections in correctional settings.

Tuberculosis: Implications for Dentistry

Tuberculosis (TB) is an airborne infection caused by Mycobacterium tuberculosis complex and is highly infectious. Therefore, precautionary measures should be implemented prior to dental treatment to reduce the risk of infection to staff and other patients. Dental history and examination have a role in identification of TB infection. Complex medical history poses a challenge to safe patient management in a dental setting, and close liaison between different disciplines in managing these patients is of paramount importance. This article explores the classical clinical features of pulmonary TB, its oral manifestations and the dental management of patients with active and latent TB. CPD/Clinical Relevance: Clinicians should be aware of the clinical features and dental management of patients with active and latent TB.

Measles and rubella are two controlled airborne infections: etiopathogenesis, epidemiology, clinical picture, diagnosis, treatment and prevention. Part 1. Measles

The lecture is devoted to two infections controlled by specific means of prevention — measles and rubella, which still pose a danger both to the sphere of child and maternal health, and to healthcare in general.
 The first part of the lecture is devoted to measles, one of the most contagious diseases, outbreaks of which can be successfully prevented through vaccination or, conversely, serve as an indicator of gaps in immunization programs and primary health care systems. The lecture covers modern aspects of etiopathogenesis, epidemiology, clinical picture, diagnosis, treatment and prevention of measles. In the context of an increase in the incidence of this infection in our country and a number of foreign countries in 2023, the information presented in the lecture may be useful for practitioners and, first of all, family doctors.

222 nm far-UVC light markedly reduces the level of infectious airborne virus in an occupied room

An emerging intervention for control of airborne-mediated pandemics and epidemics is whole-room far-UVC (200–235 nm). Laboratory studies have shown that 222-nm light inactivates airborne pathogens, potentially without harm to exposed occupants. While encouraging results have been reported in benchtop studies and in room-sized bioaerosol chambers, there is a need for quantitative studies of airborne pathogen reduction in occupied rooms. We quantified far-UVC mediated reduction of aerosolized murine norovirus (MNV) in an occupied mouse-cage cleaning room within an animal-care facility. Benchtop studies suggest that MNV is a conservative surrogate for airborne viruses such as influenza and coronavirus. Using four 222-nm fixtures installed in the ceiling, and staying well within current recommended regulatory limits, far-UVC reduced airborne infectious MNV by 99.8% (95% CI: 98.2–99.9%). Similar to previous room-sized bioaerosol chamber studies on far-UVC efficacy, these results suggest that aerosolized virus susceptibility is significantly higher in room-scale tests than in bench-scale laboratory studies. That said, as opposed to controlled laboratory studies, uncertainties in this study related to airflow patterns, virus residence time, and dose to the collected virus introduce uncertainty into the inactivation estimates. This study is the first to directly demonstrate far-UVC anti-microbial efficacy against airborne pathogens in an occupied indoor location.

The Wells-Riley model revisited: Randomness, heterogeneity, and transient behaviours.

The Wells-Riley model has been widely used to estimate airborne infection risk, typically from a deterministic point of view (i.e., focusing on the average number of infections) or in terms of a per capita probability of infection. Some of its main limitations relate to considering well-mixed air, steady-state concentration of pathogen in the air, a particular amount of time for the indoor interaction, and that all individuals are homogeneous and behave equally. Here, we revisit the Wells-Riley model, providing a mathematical formalism for its stochastic version, where the number of infected individuals follows a Binomial distribution. Then, we extend the Wells-Riley methodology to consider transient behaviours, randomness, and population heterogeneity. In particular, we provide analytical solutions for the number of infections and the per capita probability of infection when: (i) susceptible individuals remain in the room after the infector leaves, (ii) the duration of the indoor interaction is random/unknown, and (iii) infectors have heterogeneous quanta production rates (or the quanta production rate of the infector is random/unknown). We illustrate the applicability of our new formulations through two case studies: infection risk due to an infectious healthcare worker (HCW) visiting a patient, and exposure during lunch for uncertain meal times in different dining settings. Our results highlight that infection risk to a susceptible who remains in the space after the infector leaves can be nonnegligible, and highlight the importance of incorporating uncertainty in the duration of the indoor interaction and the infectivity of the infector when estimatingrisk.