Airborne spread of infectious agents in the indoor environment

Abstract

Key Words:Respiratory droplet indoor air coughing droplet dispersion infection control environmental ventilation Background: Since the 2003 severe acute respiratory syndrome epidemic, scientific exploration of infection control is no longer restricted to microbiologists or medical scientists. Many studies have reported on the release, transport, and exposure of expiratory droplets because of respiratory activities. This review focuses on the airborne spread of infectious agents from mucus to mucus in the indoor environment and their spread as governed by airflows in the respiratory system, around people, and in buildings at different transport stages. Methods: We critically review the literature on the release of respiratory droplets, their transport and dispersion in the indoor environment, and the ultimate exposure of a susceptible host, as influenced by airflows. Results: These droplets or droplet nuclei are transported by expired airflows, which are sometimes affected by the human body plume and use of a face mask, as well as room airflow. Room airflow is affected by human activities such as walking and door opening, and some droplets are eventually captured by a susceptible individual because of his or her inspired flows; such exposure can eventually lead to longrange spread of airborne pathogens. Direct exposure to the expired fine droplets or droplet nuclei results in short-range airborne transmission. Deposition of droplets and direct personal exposure to expired large droplets can lead to the fomite route and the droplet-borne route, respectively. Conclusions: We have shown the opportunities for infection control at different stages of the spread. We propose that the short-range airborne route may be important in close contact, and its control may be achieved by face masks for the source patients and use of personalized ventilation. Our discussion of the effect of thermal stratification and expiratory delivery of droplets leads to the suggestion that displacement ventilation may not be applicable to hospital rooms where respiratory infection is a concern.

Assessment of a respiratory face mask for capturing air pollutants and pathogens including human influenza and rhinoviruses

“…For example, Lindsley et al (27) measured the content of influenza virus in aerosol particles from human coughs, reporting that 35% of the influenza RNA detected was contained in particles >4 μm in aerodynamic diameter, whereas 23% were contained in particles of 1-4 μm diameter and 42% were in particles <1 μm in diameter, indicating that the majority of the viral RNA from human coughs was within the respirable size range. Also, aerosols generated by coughing patients infected with Mycobacterium tuberculosis were between the range of 0.65-4.7 μm in diameter (29).…”

Meteorological factors and the incidence of mumps in Fujian Province, China, 2005–2013: Non-linear effects

“…The maximum or minimum values of variables generally represent the extreme weather conditions that help the virus development and transmission. For example, low wind velocity and high atmospheric pressure can increase the virus concentration in a certain room by hindering the airflow (Morawska, 2006;Wei and Li, 2016) and low sunshine duration will do less harm to the virus (Walker and Ko, 2007), as mentioned before. Furthermore, immune status and behavior pattern of individual may change in extreme weather conditions.…”

“…Whereas another research showed no effect of atmospheric pressure on HFMD . Considering that the occurrence of mumps is clustered and half of the mumps patients are students, the high atmospheric pressure and low wind velocity may increase the virus concentration in a certain classroom by hindering the airflow, particularly in winter, and then increase the incidence of mumps (Morawska, 2006;Wei and Li, 2016).…”

Human Cough as a Two-Stage Jet and Its Role in Particle Transport

“…Exposure to these pathogen-containing droplets can occur via both short- (within 1–2 m of the source patient) and long- (beyond about 2 m in the indoor environment) range routes. The former is known as direct spray infection [2], in which relatively large (≥ 5 μm in diameter) droplets or droplet nuclei can be directly deposited on the nasal or oral mucosa of the new host. Short-range airborne exposure via smaller droplets or droplet nuclei is also important in close proximity infection [3].…”