key: cord-1043264-hc3h4ufg
authors: Li, Yuguo
title: The respiratory infection inhalation route continuum
date: 2021-02-23
journal: Indoor Air
DOI: 10.1111/ina.12806
sha: bcea783c88f5836e8a7b501d04b954bd5184bdd4
doc_id: 1043264
cord_uid: hc3h4ufg

nan

SARS-CoV-2 is not the only virus about which there is significant uncertainty regarding transmission routes. Confusion and doubt have existed for a long time over the role of inhalation in the transmission of other respiratory infections. For example, one review concluded that influenza viruses can be transmitted by inhalation, 1 whereas another concluded the opposite. 2 Significantly, both of these studies examined the same well-known Alaska plane outbreak, 3 in which 72% of the 54 passengers were infected with influenza and the estimated maximum ventilation rate was 0.4 L/s per passenger. 4 These opposing conclusions illustrate what I would refer to as the aerosol inconsistency phenomenon.

In an earlier editorial that described basic transmission routes for respiratory infection, 5 (aerosol) inhalation transmission was defined as the infection of a susceptible individual via the inhalation of virusladen respiratory droplets, that is, aerosols suspended in the air.

Aerosol inhalation can occur at short range (when in close contact with an infected person) or at long range (when across a room from an infected individual). In the literature, short-range inhalation is also referred to as the short-range airborne route, while long-range inhalation is known as the airborne route.

In earlier outbreak studies, such as those of the Alaska plane It may be useful to visualize two zones in a room: a zone within close range of the expired jet of the infected person, and a zone comprising the remainder of the room, as shown in Figure 1 . Recognizing F I G U R E 1 Illustration of the infection risk in the close-range zone (in light green, representing a breathing case) and that in the remainder of a room (long-range zone). The infection risk reduces as the inter-personal distance increases, as shown by the thick gray line. The spread of the expired jet depends on head/body movement. When the jet spread angle is narrow, passive tracer-gas decay follows the 1/d rule, where d is the distance; when the angle is wide, the 1/d 2 rule applies Air speed (<0.25 m/s); Droplet stays for hours; All droplets fully evaporate and shrink to a smaller size; Droplets 5-10 microns or smaller can be airborne; Low concentra on of airborne droplets; Less viable viruses.

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