Despite formidable advances in virology and medicine in recent decades, we know remarkably little about the dynamics of the influenza virus in the environment during transmission between hosts. There is still controversy over the relative importance of various transmission routes, and the seasonality of influenza remains unexplained. This work focuses on developing new knowledge about influenza transmission via the airborne route and the virus' inter-host dynamics in droplets and aerosols. We measured airborne concentrations of influenza A viruses (IAVs) and size distributions of their carrier aerosols in a health center, a daycare center, and airplanes. Results indicate that the majority of viruses are associated with aerosols smaller than 2.5 µm and that concentrations are sufficient to induce infection. We further modeled the fate and transport of IAV-laden droplets expelled from a cough into a room, as a function of relative humidity (RH) and droplet size. The model shows that airborne concentrations of infectious IAV vary with RH through its influence on virus inactivation and droplet size, which shrinks due to evaporation. IAVs associated with large droplets are removed mostly by settling, while those associated with aerosols smaller than 5 µm are removed mainly by ventilation and inactivation. To investigate the relationship between RH and influenza transmission further, we measured the viability of IAV in droplets at varying RHs. Results suggest that there exist three regimes defined by RH: physiological conditions (~100% RH) with high viability, concentrated conditions (~50% to ~99% RH) with lower viability, and dry conditions (<~50% RH) with high viability. A droplet's extent of evaporation, which is determined by RH, affects solute concentrations in the droplet, and these appear to influence viability. This research considerably advances the current understanding of the dynamics of the influenza virus while it is airborne and provides an explanation for influenza's seasonality. Increased influenza activity in winter in temperate regions could be due to greater potential for IAV carrier aerosols to remain airborne and higher viability of IAV at low RH. In tropical regions, transmission could be enhanced due to better survival of IAV at extremely high RH. / Ph. D.

The emergence of coronavirus disease 2019 (COVID-19) has resulted in more than 300 million cases and 5 million deaths worldwide and innumerable economic losses. COVID-19 is acknowledged to transmit via air, but whether it is capable of transmitting via contaminated surfaces, also known as fomites, remains controversial. The overarching goal of this study was to investigate the presence and stability of SARS-CoV-2, the virus that causes COVID-19, on indoor surfaces and masks, and to provide insight into the possibility of fomite transmission. Since most transmission occurs indoors where humans spent 90% of their time, we first focused on quantifying the contamination level of SARS-CoV-2, including both viral RNA and viable virus, on commonly touched surfaces and in the heating, ventilation, and air cleaning (HVAC) systems in two university dormitories. Although we found up to 104 gene copies per ~10×10 cm2 on surfaces, we did not detect any viable virus, suggesting that the possibility of transmission via indoor surfaces is low. As universal masking has been recommended as an effective practice to prevent transmission of SARS-CoV-2, we shifted our focus to masks, both their effectiveness at filtering the virus from the air and their potential to serve as fomites. We evaluated the effectiveness of 11 face coverings for material filtration efficiency, inward protection efficiency on a manikin, and outward protection efficiency on a manikin. Masks made of filter materials, such as vacuum cleaner bag and HVAC filters, achieved a high material filtration efficiency whereas common textiles like cotton and acrylic usually showed the worst performance. The material filtration efficiency was generally positively correlated with either inward or outward protection effectiveness, but stiffer materials were an exception to this relationship as they did not fit as closely to the manikin's face and thus leaked substantially. Subsequently, we analyzed the survival of aerosolized SARS-CoV-2 in saliva on masks. Results suggested that the virus lost infectivity within one hour on an N95 respirator, surgical mask, polyester mask, and two types of cotton masks but not on a nylon/spandex mask. This study also highlighted the importance of applying virus in aerosols of realistic sizes when analyzing the stability of SARS-CoV-2 on surfaces. / Doctor of Philosophy / The emergence of coronavirus disease 2019 (COVID-19) has resulted in more than 300 million cases and 5 million deaths worldwide and innumerable economic losses. Researchers are debating if COVID-19 can transmit via surfaces contaminated with SARS-CoV-2, the virus that causes the disease. The goal of this study was to investigate whether SARS-CoV-2 is present and remains viable on indoor surfaces and masks, and to provide insight into the possibility of transmission via contaminated surfaces. Since most transmission occurs indoors where humans spent 90% of their time, we first focused on quantifying number of SARS-CoV-2 on commonly touched surfaces and in the heating, ventilation, and air cleaning (HVAC) systems in two university dormitories. Although we found a high concentration of SARS-CoV-2 genes on surfaces, we did not detect any viable virus, suggesting that the possibility of transmission via indoor surfaces is low. As universal masking has been recommended as an effective practice to prevent transmission of SARS-CoV-2, we shifted our focus to masks. We evaluated the effectiveness of 11 face coverings regarding their ability to trap viruses, protect wearers from inhaling viruses, and prevent infected individuals from expelling viruses into the surrounding air. Masks made of filter materials, such as a vacuum cleaner bag and HVAC filter, trapped the most viruses whereas common textiles like cotton and acrylic usually performed worst. It is also crucial that masks fit closely to the wearer's face to achieve better protection. Subsequently, we analyzed the ability of SARS-CoV-2 in aerosols, microscopic particles such as those exhaled by an infected person, to survive on different types of masks. Results suggested that the virus died within one hour on a majority of the masks. This study also highlighted the importance of applying aerosols of realistic sizes instead of large droplets when analyzing the survival of SARS-CoV-2 on surfaces.

Pathogen-containing droplets expelled into the air as infected individuals speak, cough, sneeze, or laugh may infect proximal secondary hosts. Facemasks are an effective, low-cost method to help prevent airborne transmission mediated by pathogen-laden droplets in the environment. To understand the testing of facemask materials to protect against airborne pathogens, we followed the American Society for Testing and Materials (ASTM) standard F2101-12 and built an in-house test platform. However, the standard lacks clear guidelines. To address this, we built an aerosol platform at McMaster University to generate and test droplets containing viable bacteria, allowing us to assess the filtration performance of different facemask materials. We created optimized procedures to ensure the generation and sampling of infectious aerosols are consistent and reliable. The operation, maintenance, and sterilization of the platform were also detailed. Airborne disease transmission is a complex phenomenon influenced by multiple factors. Conditions such as muco-obstructive airway disorders can increase the viscosity and solute content of airway lining fluid. Therefore, individual variability in airway mucus composition and initial droplet size may influence transmission dynamics. Thirdly, environmental conditions such as temperature and humidity can change the aerosol microenvironment and alter encapsulated pathogen viability. Evidence suggests infectious aerosols originate from the breakup of the airway lining fluid, and the site of origin within the airways can affect the size of pathogen-laden droplets. Using the bacteriophage Phi6 as a stand-in for the SARS-CoV-2 virus, we examined how droplet size, mucus composition, pathogen load, and environmental conditions (temperature and humidity) affect pathogen survival. Our findings may provide insight into the dynamics of airborne transmission and can help improve strategies to reduce the spread of respiratory infections. Lastly, we adapted the platform to conduct in vitro lung exposure studies of deposition, safety, and efficacy of bactericidal agents. The human airway epithelial cell line, Calu-3, cultured in an air-liquid interface system, was used to recapitulate the physiological characteristics of the respiratory mucosa. Pseudomonas aeruginosa biofilms cultured for 24 hours were placed within the impactor and exposed to aerosolized bactericidal agents. Preliminary results show that our cell-integrated exposure platform can assess in vitro safety, efficacy, and dosage of inhaled therapeutics. This setup can potentially help gather pre-clinical data to support in vivo studies of treatments for respiratory diseases. This platform has significant potential for expanding aerosol research at McMaster University to evaluate the effectiveness of personal protective equipment, study how infectious aerosols spread, and explore inhaled delivery of therapeutic agents to the lungs. These findings contribute to our understanding of airborne transmission and may inform strategies to reduce the spread of infections. / Thesis / Doctor of Philosophy (PhD) / Many respiratory infections are spread through the air by pathogen-containing droplets released from the airways of infected individuals as they breathe, talk, cough, sneeze, or laugh. Facemasks are an easy-to-adopt infection control strategy to guard against airborne infectious agents. An aerosol platform was built at McMaster University amidst the coronavirus pandemic to perform facemask material filtration tests using information from the American Society for Materials and Testing standard F2101-19. However, we soon identified ambiguous aspects of the standard that can potentially prevent the reliable operation of the test platform and the gathering of reproducible test results. The first objective was to modify the test setup and develop precise procedures to address ambiguities of the standard. Modifications of the platform and detailed procedures ensured more accurate and consistent testing of facemask materials. Next, we used the platform to study how long pathogens stay viable within aerosol droplets. Droplets containing the bacteriophage Phi6, a surrogate for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), were used to study how droplet size, mucus composition, and environmental conditions (like temperature and humidity) affect pathogen survival. Lastly, we adapted our aerosol platform to investigate the inhaled delivery of antibacterial agents to target lung infections. Using cultures of human airway epithelial cells and Pseudomonas aeruginosa biofilms, we tested the antibacterial efficacy of aerosolized antibiotics and bacteriophages (viruses that kill bacteria). In summary, this thesis work has developed an aerosol platform for conducting reliable material filtration efficiency tests, probing virus stability within airborne droplets, and modelling inhaled drug delivery to the lungs.

Orientador: Luiz Fernando de Oliveira e Silva Carvalho / Banca: Raul José Silva Girio / Banca: Rosangela Zacarias Machado / Banca: Aníbal de Sant'Anna Moretti / Banca: José Soares Ferreira Neto / Resumo: Os suínos e seus produtos são considerados importantes fontes de salmonelose humana. Desta forma, o controle das infecções nas granjas é considerado essencial para a prevenção de Salmonella na cadeia produtiva de suínos. No entanto, o maior entrave na profilaxia da infecção é, principalmente, a falta de conhecimentos sobre sua epidemiologia em sistemas de produção intensivos de criação de suínos, principalmente em relação às possíveis vias de transmissão desse agente. Este estudo testou a hipótese da transmissão nasonasal (E1) e aerógena (E2) de Salmonella Derby na espécie suína. Os experimentos foram realizados em isoladores construídos em aço inoxidável e vidro e totalmente controlados. No E1, os isoladores dos suínos inoculados e dos suínos sentinela estavam conectados por pequena fenda que permitia apenas o contato naso-nasal. Em E2 os isoladores estavam conectados por condutores de ar que permitiam o fluxo de ar unidirecional do isolador 1 (suínos controle) ao isolador 3 (suínos sentinela), passando pelo isolador 2 (suínos inoculados). A duração de ambos experimentos foi de 15 dias. Nesse período, amostras dos sacos de dejetos, dos suabes retais, das fezes do piso e do ar foram colhidas diariamente e avaliadas quanto a presença de Salmonella. A hipótese de transmissão naso-nasal e aerógena de S. Derby não foi corroborada pelo isolamento e detecção do agente nos animais sentinela. / Abstract: Pork and pork products are recognized as one of the major sources for human salmonellosis. Howeveri the infection control in the farms is considered essential for the Salmonella prevention in the productive swine chain. However, the most impediment in the infection prophylaxis is, mainly, the lack of knowledge on its epidemiology in intensives production systems, mainly related to the transmission possible ways of this agent. This study has tested the hypothesis of nose-to-nose and airborne transmission of Salmonella Derby in the swine species. The trials were performed using stainlesssteel and glass isolation cabinets and totally controlled. In the trial 1, inoculated pigs and sentinel pigs isolation cabinets were connected by small crack that allowed only the nose-to-nose contact. In the trial 2 isolation cabinets were connected by air ducts that allowed an unidirectional airflow from cabinet 1 (control pigs) to cabinet 3 (sentinel pigs), passing through cabinet 2 (inoculated pigs). The duration of both trials were 15 days. At this period, slurry bags, rectal swabs, pooled faecal from the floor and air samples were collected daily and assessed by culture and PCR. The nose-to-nose and airborne transmission hypothesis of S. Derby was not corroborated by the agent isolation and detection in the sentinel pigs. / Doutor

This research used computational fluid dynamics (CFD) to examine the behavior of airborne droplets released during respiratory events. The CFD model utilizes an Eulerian-Lagrangian approach, with turbulence resolved using the Spalart-Allmaras detached eddy simulation. The first part investigates airborne transmission and how modifying saliva during a sneeze impacts this process. The study employs CFD to simulate these respiratory events in a ventilated room. It finds that larger droplets alone are insufficient for droplet settling due to secondary breakdown processes. Modifiers that increase the Ohnesorge number show resistance to aerosolization from secondary breakup, resulting in more droplets with high settling rates, reducing their likelihood of airborne transmission. Another effective modifier reduces saliva content. The second part of the research develops a linear algebraic function to represent the near-field dispersion of droplets formed during respiratory events. This model facilitates the examination of flow interaction among various sources in different environments without requiring computationally expensive CFD simulations. The final part of the research involves developing a numerical Wells curve considering droplet evaporation, buoyancy, turbulence, breakup, and collision. The study also examines the effect of relative humidity on airborne transmission, finding that higher relative humidity slows the evaporation rate, which typically promotes faster droplet settling. Overall, these findings offer promising strategies for preventing spread of airborne transmission, highlighting the potential of saliva modification and advanced modeling techniques in public health interventions.

As the world observes a new pandemic with COVID-19, it is clear that pathogens can spread rapidly and without recognition of borders. Outbreaks will continue to occur, and so the diseases’ transmission method must be thoroughly understood in order to minimize their impact. Some infections, such as influenza, tuberculosis and measles are known to be spread through droplets in the air. In a confined space the concentration can grow as more droplets are released. This study examined a simulated confined space modelled as a hospital waiting area, where people who could have underlying conditions congregate and mix with potentially infectious individuals. It further investigated the impact of the volume of the waiting area, the number of people in the room, the placement of them as well as their weight. The simulation is an agent-based model (ABM), a computational model with the purpose of analysing a system through the actions and cumulative consequences of autonomous agents. The presented ABM features embodied agents with differing body weights that can move, breathe and cough in a ventilated room. An investigation into current epidemiological models lead to the hypothesis that one may be implemented as a corresponding ABM, where it could possibly also be improved upon. In this paper, it is shown that all parameters of the Gammaitoni and Nucci model can be taken into account in an ABM via the MASON library. In addition, proof is produced to suggest that some flaws of the epidemiological model can be mended in the ABM. It is demonstrated that the constructed model can account for proximity between susceptible people and infectors, an expressed limitation of the original model. / När världen observerar en ny pandemi, COVID-19, är det tydligt att patogener kan spridas fort och utan hänsyn till landsgränser. Utbrott kommer att fortsätta ske och därför måste sjukdomarnas överföringsmetod förstås, så att deras påverkan kan minimeras. Det är känt att vissa infektioner, såsom influensa, tuberkulos och mässling kan spridas via droppkärnor i luften. I ett begränsat utrymme kan koncentrationen växa när fler droppar tillförs. Denna studie utvärderar ett simulerat begränsat utrymme modellerat som ett väntrum på ett sjukhus, där människor som kan ha underliggande sjukdomar samlas och beblandar sig med potentiellt smittsamma individer. Inverkan av volymen av väntrummet, antalet personer i rummet, var de var placerade i rummet samt deras vikt undersöktes också. Simuleringen är en agent-baserad modell (ABM), en beräkningsmodell med syftet att analysera ett system genom handlingarna och kumulativa konsekvenserna av självstyrande agenter. Personer med olika kroppsvikt som kan röra sig, andas och hosta i ett ventilerat rum simuleras i denna ABM. Efterforskning av aktuella epidemiologiska modeller leder till hypotesen att en sådan skulle kunna implementeras som en motsvarande ABM, där den möjligtvis också kan förbättras. I denna rapport kommer det att uppvisas att alla parametrar av Gammaitonioch Nucci-modellen kan tas hänsyn till i en ABM via MASON biblioteket. Därtill produceras bevis som pekar på att vissa brister i den epidemiologiska modellen kan hämmas i denna ABM. Det demonstreras att den konstruerade modellen kan beakta distansen mellan mottagliga personer och smittsamma, vilket är en känd begränsning i originalmodellen.

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