Toward Understanding the Risk of Secondary Airborne Infection: Emission of Respirable Pathogens

Abstract

Certain respiratory tract infections are transmitted through air. Coughing and sneezing by an infected person can emit pathogen-containing particles with diameters less than 10 microm that can reach the alveolar region. Based on our analysis of the sparse literature on respiratory aerosols, we estimated that emitted particles quickly decrease in diameter due to water loss to one-half the initial values, and that in one cough the volume in particles with initial diameters less than 20 microm is 60 x 10(-8) mL. The pathogen emission rate from a source case depends on the frequency of expiratory events, the respirable particle volume, and the pathogen concentration in respiratory fluid. Viable airborne pathogens are removed by exhaust ventilation, particle settling, die-off, and air disinfection methods; each removal mechanism can be assigned a first-order rate constant. The pathogen concentration in well-mixed room air depends on the emission rate, the size distribution of respirable particles carrying pathogens, and the removal rate constants. The particle settling rate and the alveolar deposition fraction depend on particle size. Given these inputs plus a susceptible person's breathing rate and exposure duration to room air, an expected alveolar dosemicrois estimated. If the infectious dose is one organism, as appears to be true for tuberculosis, infection risk is estimated by the expression: R = 1-exp(-micro). Using published tuberculosis data concerning cough frequency, bacilli concentration in respiratory fluid, and die-off rate, we illustrate the model via a plausible scenario for a person visiting the room of a pulmonary tuberculosis case. We suggest that patients termed "superspreaders" or "dangerous disseminators" are those infrequently encountered persons with high values of cough and/or sneeze frequency, elevated pathogen concentration in respiratory fluid, and/or increased respirable aerosol volume per expiratory event such that their pathogen emission rate is much higher than average.

Aerosolization of Ebola Virus Surrogates in Wastewater Systems

“…[36][37][38] The concentration of airborne bacteria has been shown to vary from as low as 4 to 1000s of CFU m -3 depending on the species. 33,[39][40][41] Airborne viruses have been detected at WWTPs as well. Adenovirus and norovirus concentrations as high as 2.27 × 10 6 genome copies m -3 and 1.42± 1.14 × 10 3 genome copies m -3 , respectively, have been reported.…”

Dispersion of Expiratory Droplets in a General Hospital Ward with Ceiling Mixing Type Mechanical Ventilation System

“…The initial droplet size distribution of the injection was adopted from the coughing size distribution reported in literatures. As reviewed by Nicas et al (2005), there are three major studies about the size distribution of expiratory droplets available in the literature. Papineni and Rosenthal (1997) employed optical particle counters (OPCs) and transmission electron microscope analysis, which covered the size range of only 0.3-8 μm.…”

“…Duguid (1946) and Louden and Roberts (1967) employed a stain-mark-counting approach, which covered a droplet size range (from 1 to over 1000 μm) much wider than that reported by Papineni and Rosenthal (1997). The data reported by Papineni and Rosenthal (1997) may also suffer from sampling and transmission losses in the OPCs, as indicated by Nicas et al (2005). Comparing with a bioaerosols study, Nicas et al (2005) judged that the size distributions of Duguid (1946) and Loudon and Roberts (1967) were consistent with the study findings but inconsistent with Papineni and Rosenthal (1997).…”

Viable influenza A virus in airborne particles expelled during coughs versus exhalations

“…Humans produce more aerosol particles when they cough vs. when they exhale 27, 28. Most of the aerosol particles produced during normal breathing are thought to originate deep in the respiratory tract, while coughing may produce aerosol both from the lower airways and also from the upper airways 29, 30, 31.…”