The article by Mark Nicas, William W. Nazaroff, and Alan Hubbard explores the risk of secondary airborne infection from respiratory tract infections, focusing on the emission and transmission of pathogen-containing particles. Coughing and sneezing can release particles with diameters less than 10 μm, which can reach the alveolar region and cause infection. The authors estimate that these particles quickly decrease in size due to water loss, and the volume of particles with initial diameters less than 20 μm in a single cough is 6 × 10−8 mL. The pathogen emission rate depends on the frequency of expiratory events, the volume of respirable particles, and the concentration of pathogens in respiratory fluid. Pathogens are removed from room air through exhaust ventilation, particle settling, die-off, and air disinfection, each with its own removal rate constant. The concentration of pathogens in well-mixed room air depends on the emission rate, the size distribution of respirable particles, and the removal rate constants. The authors estimate the expected alveolar dose and use it to calculate the infection risk, particularly for tuberculosis, where the infectious dose is one organism. They illustrate their model with a scenario involving a person visiting a room where a pulmonary tuberculosis case is present, suggesting that "superspreaders" are those individuals with high cough and sneeze frequencies, elevated pathogen concentrations, and increased aerosol volume per expiratory event, leading to higher pathogen emission rates.The article by Mark Nicas, William W. Nazaroff, and Alan Hubbard explores the risk of secondary airborne infection from respiratory tract infections, focusing on the emission and transmission of pathogen-containing particles. Coughing and sneezing can release particles with diameters less than 10 μm, which can reach the alveolar region and cause infection. The authors estimate that these particles quickly decrease in size due to water loss, and the volume of particles with initial diameters less than 20 μm in a single cough is 6 × 10−8 mL. The pathogen emission rate depends on the frequency of expiratory events, the volume of respirable particles, and the concentration of pathogens in respiratory fluid. Pathogens are removed from room air through exhaust ventilation, particle settling, die-off, and air disinfection, each with its own removal rate constant. The concentration of pathogens in well-mixed room air depends on the emission rate, the size distribution of respirable particles, and the removal rate constants. The authors estimate the expected alveolar dose and use it to calculate the infection risk, particularly for tuberculosis, where the infectious dose is one organism. They illustrate their model with a scenario involving a person visiting a room where a pulmonary tuberculosis case is present, suggesting that "superspreaders" are those individuals with high cough and sneeze frequencies, elevated pathogen concentrations, and increased aerosol volume per expiratory event, leading to higher pathogen emission rates.