The article discusses the risk of secondary airborne infection, focusing on the emission of respirable pathogens. It highlights that respiratory infections can be transmitted through air via coughing and sneezing, which emit pathogen-containing particles with diameters less than 10 micrometers. These particles can reach the alveolar region of the lungs. The study estimates that in one cough, the volume of particles with initial diameters less than 20 micrometers is 6×10⁻⁸ mL. The pathogen emission rate depends on factors such as the frequency of expiratory events, the respirable particle volume, and the pathogen concentration in respiratory fluid. Pathogens are removed from the air through various mechanisms, including exhaust ventilation, particle settling, die-off, and air disinfection. The concentration of pathogens in well-mixed room air depends on emission rate, size distribution of respirable particles, and removal rate constants. The study also considers the effects of evaporative water loss on particle size, showing that emitted particles can shrink to about half their initial diameter. The alveolar deposition fraction depends on particle size, and the expected alveolar dose is estimated based on a susceptible person's breathing rate and exposure duration. For tuberculosis, infection risk is estimated using the formula R = 1 - exp(-μ), where μ is the alveolar dose. The study uses published tuberculosis data to illustrate the model through a plausible scenario for a person visiting the room of a pulmonary tuberculosis case. It suggests that individuals termed "superspreaders" have high values of cough and/or sneeze frequency, elevated pathogen concentration in respiratory fluid, and/or increased respirable aerosol volume per expiratory event, leading to higher pathogen emission rates. The study also discusses the size distribution of respiratory aerosol, the effects of evaporative water loss, and the use of nonparametric methods to estimate the volume of respirable pathogen-carrying particles. It highlights the importance of considering particle size distribution in estimating airborne infection risk and the limitations of using lognormal models for respiratory particle diameters. The study concludes that while the vast majority of emitted pathogens are carried by particles that do not reach the alveolar region, small particles can still pose an appreciable infection risk. The study also discusses the implications of particle size on infection risk, the role of evaporative water loss in reducing particle size, and the importance of considering the health status of individuals in estimating infection risk. The study provides a framework for estimating the risk of airborne infection by considering factors such as particle size, emission rate, and removal mechanisms.The article discusses the risk of secondary airborne infection, focusing on the emission of respirable pathogens. It highlights that respiratory infections can be transmitted through air via coughing and sneezing, which emit pathogen-containing particles with diameters less than 10 micrometers. These particles can reach the alveolar region of the lungs. The study estimates that in one cough, the volume of particles with initial diameters less than 20 micrometers is 6×10⁻⁸ mL. The pathogen emission rate depends on factors such as the frequency of expiratory events, the respirable particle volume, and the pathogen concentration in respiratory fluid. Pathogens are removed from the air through various mechanisms, including exhaust ventilation, particle settling, die-off, and air disinfection. The concentration of pathogens in well-mixed room air depends on emission rate, size distribution of respirable particles, and removal rate constants. The study also considers the effects of evaporative water loss on particle size, showing that emitted particles can shrink to about half their initial diameter. The alveolar deposition fraction depends on particle size, and the expected alveolar dose is estimated based on a susceptible person's breathing rate and exposure duration. For tuberculosis, infection risk is estimated using the formula R = 1 - exp(-μ), where μ is the alveolar dose. The study uses published tuberculosis data to illustrate the model through a plausible scenario for a person visiting the room of a pulmonary tuberculosis case. It suggests that individuals termed "superspreaders" have high values of cough and/or sneeze frequency, elevated pathogen concentration in respiratory fluid, and/or increased respirable aerosol volume per expiratory event, leading to higher pathogen emission rates. The study also discusses the size distribution of respiratory aerosol, the effects of evaporative water loss, and the use of nonparametric methods to estimate the volume of respirable pathogen-carrying particles. It highlights the importance of considering particle size distribution in estimating airborne infection risk and the limitations of using lognormal models for respiratory particle diameters. The study concludes that while the vast majority of emitted pathogens are carried by particles that do not reach the alveolar region, small particles can still pose an appreciable infection risk. The study also discusses the implications of particle size on infection risk, the role of evaporative water loss in reducing particle size, and the importance of considering the health status of individuals in estimating infection risk. The study provides a framework for estimating the risk of airborne infection by considering factors such as particle size, emission rate, and removal mechanisms.