The size of the generated particles ranged from 0.35 to 9 μm. Among the particles generated by the influenza-infected patients, particles with a size range of 0.35–2.5 μm were of higher number concentration. Furthermore, these particles could remain airborne for dozens of minutes to several hours
Small particles that can be airborne are defined as aerosol particles [10]. Several experimental results support the view that respiratory particles are sufficiently small for airborne transmission of microorganisms inside the particles. In a study by Johnson et al. (2011), it was reported that healthy subjects (8–15 humans) generate various particles—including respiratory droplets—of three size modes during speech and voluntary coughing (1.6, 2.5 and 145 μm, and 1.6, 1.7 and 123 μm, respectively) [11]. These particles contained very large respiratory droplets with sizes exceeding 100 μm, which fell to the ground within a few seconds. However, in the experimental results, small particles of approximately 2 μm were generated simultaneously [11] and they could remain airborne for dozens of minutes.
In another study by Lindsley et al. (2012), the sizes of aerosol particles generated by patients (9 subjects) who were infected by the influenza virus were measured [12]. The size of the generated particles ranged from 0.35 to 9 μm. Among the particles generated by the influenza-infected patients, particles with a size range of 0.35–2.5 μm were of higher number concentration. Furthermore, these particles could remain airborne for dozens of minutes to several hours [10]. Therefore, the detected particles from influenza-infected patients were estimated to be mainly airborne for significant periods.
Aerosol particles from patients (10 subjects) with an upper respiratory tract infection were measured by Lee et al. (2019) under clean air conditions [13]. The size of the particles generated from these patients ranged from <0.1 μm to 10 μm. A significant number of particles <1 μm in size were generated by the coughing patients. The results of these studies, conducted on healthy humans, influenza-infected patients and patients with upper respiratory tract infections, demonstrated that a significant amount of respiratory particles that are sufficiently small to be airborne for at least several minutes are generated. Therefore, airflow can transport these particles over time.
Additionally, the characteristics of the generated respiratory particles in the aforementioned studies were found to be related to human health conditions. For instance, in studies conducted on patients suffering from influenza and upper respiratory tract infections, the number of generated aerosol particles decreased when the subjects recovered from diseases [12,13].
Bookmarks