The main aspects of influenza transmission via fine and ultrafine bioaerosols were considered. Here, we aimed to estimate the impact of the different environment conditions on the processes of heat and mass transfer in the upper respiratory tract and its role in the deposition rate of the infectious bioaerosols in the lungs.
The latest researches show the infected people generate the fine and ultrafine infectious bioaerosols with submicron particles/droplets (size below 1 µm). The airborne transmission of these particles/droplets is effective. It is considered the deposition of submicron particles in the respiratory tract (RT) has very low probability. But most studies examined the deposition of the particles in the lungs under normal environmental conditions and did not paid attention to the different environmental factors.
We review the problems of epidemiology of respiratory infections and aspects of airborne transmission/spread of infectious agents. We contrast these approaches with known data from next area: inhalation toxicology, respiratory drug delivery and physics of heat and mass transfer in the airways.
On the basis of these analyses, we propose the next main concepts:
1 Breathing cool air leads to the supersaturation of air in RT;
2 the air supersaturation leads to the intensive condensational growth(CG) of inhaled viruses or bacteria in RT;
3 CG leads to the intensive and dramatically growth of deposition rate of viruses or bacteria in RT.
We have shown:
a) Under normal conditions of inhaled air (T>20˚C; Relatively Humidity (RH)=60%) there is no transition in supersaturated condition in RT and CG is insignificant and probability of virus deposition on epithelium of RT is low – no more than 20%.
b) Breathing cool/cold air of T<+15˚C and RH of [30..60]% leads to the supersaturation in the airways and it can dramatically increase the deposition rate of inhaled bioaresols in the lungs (up to 97%).
c) With an increase in RH of inhaled air the supersaturation in RT occurs even at warm temperature of inhaled air (for inhaled air of T<20°C and RH>70% ; T<25°C and RH>90%). It also indicates the high deposition rate of bioaerosols in the lungs.
Under specific environmental conditions (when flu seasons) the processes of supersaturation in the RT can be observed. These results indicate the high probability of virus deposition on epithelium of RT and correspond to influenza and seasonal respiratory infections in temperate and tropical climates.
We believe the effect of supersaturation in the lungs can be the key to understanding of ‘the age-old epidemiologic mystery of influenza seasonality in the different climatic conditions’.