Effect of ambient humidity and temperature on transmission probability.

<p>The predicted probability of transmission at varied temperatures versus (A, C) relative humidity and (B, D) absolute humidity for the pulmonary (A–B) and NPTB (C–D) deposition efficiencies at 10 cm and 30 cm downstream, respectively. The experimental observations by Lowen <i>et al. </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037088#pone.0037088-Lowen2" target="_blank">[4]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037088#pone.0037088-Lowen3" target="_blank">[5]</a> are shown as discrete points. Blue circles: T = 5°C; gray triangles: T = 20°C; red squares: T = 30°C.</p

Probability of transmission at different positions for rPan99 and Tx91 experiments.

<p>Contour plot of transmission probability in (A) rPan99 experiment with χ = 1, (B) Tx91 experiment with χ = 1, and (C) Tx91 experiment with χ = .135 using the NPTB deposition efficiency. At x≈7 cm, transmission probabilities match the findings of Mubareka <i>et al. </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037088#pone.0037088-Mubareka1" target="_blank">[6]</a> (A, C).</p

Droplet size evolution and deposition efficiencies.

<p>(A) Aerosol size versus time for droplets in air at 50% RH. Solid lines, <i>a₀</i> = 5 µm; dotted lines, <i>a₀</i> = 15 µm. Blue curves: T = 5°C; red curves: T = 30°C. (B) The deposition efficiency of a unit-density particle of radius <i>a</i> depositing in the pulmonary (P) and nasopharyngeal-tracheobronchial (NPTB) regions of a guinea pig. Purple: Pulmonary; black: NPTB. Reproduced from Schreider <i>et al. </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037088#pone.0037088-Schreider1" target="_blank">[34]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037088#pone.0037088-Schreider2" target="_blank">[35]</a>.</p

Guinea pig viral growth kinetics of rPan99 and Tx91.

<p>The measurements by Mubareka <i>et al. </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037088#pone.0037088-Mubareka1" target="_blank">[6]</a> of the influenza concentration observed in nasal titers obtained from inoculated guinea pigs infected with rPan99 and Tx91. Black circles: rPan99; purple squares: Tx91. Dashed lines are fits to a numerical model for influenza viral dynamics <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037088#pone.0037088-Baccam1" target="_blank">[18]</a>.</p

Probability of transmission at different positions.

<p>Contour plots of the probability of transmission as a function of position downstream from an infected animal located at the origin for the pulmonary (A–F) and NPTB (G–L) deposition efficiencies. Red denotes high probability of transmission, blue denotes low probability. (A–C, G–I) Fixed relative humidity and varying temperature. (D–F, J–L) Fixed temperature and varying relative humidity. Note that the transmission probability depends strongly on temperature but more weakly on humidity.</p

Sensitivity analysis of viral kinetics and airflow parameters for NPTB deposition efficiency 30 cm downstream.

<p>(A) Contour plot of transmission probability as a function of <i>n_p^{drop, max}</i> and <i>t_peak</i>. The animals are assumed to be brought into contact one day post-inoculation and removed seven days later. (B) Contour plot of transmission probability as a function of the turbulent dispersivity coefficients <i>i_y</i>, <i>i_z</i> (assumed equal) and mean airflow velocity <i>U</i>. Small changes in either the degree of turbulence or the flow velocity yield large changes in the transmission probability.</p

Guinea pig viral growth kinetics at different temperatures.

<p>The measurements by Lowen <i>et al. </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037088#pone.0037088-Lowen2" target="_blank">[4]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037088#pone.0037088-Lowen3" target="_blank">[5]</a> of the influenza concentration observed in nasal titers obtained from inoculated guinea pigs maintained at different temperatures. Blue circles: T = 5°C; red squares: T = 30°C. Dashed lines are fits to a numerical model for influenza viral dynamics <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037088#pone.0037088-Baccam1" target="_blank">[18]</a>; solid lines are analytical estimates given by Equation 1.</p

A Comprehensive Breath Plume Model for Disease Transmission via Expiratory Aerosols

<div><p>The peak in influenza incidence during wintertime in temperate regions represents a longstanding, unresolved scientific question. One hypothesis is that the efficacy of airborne transmission via aerosols is increased at lower humidities and temperatures, conditions that prevail in wintertime. Recent work with a guinea pig model by Lowen <em>et al.</em> indicated that humidity and temperature do modulate airborne influenza virus transmission, and several investigators have interpreted the observed humidity dependence in terms of airborne virus survivability. This interpretation, however, neglects two key observations: the effect of ambient temperature on the viral growth kinetics within the animals, and the strong influence of the background airflow on transmission. Here we provide a comprehensive theoretical framework for assessing the probability of disease transmission via expiratory aerosols between test animals in laboratory conditions. The spread of aerosols emitted from an infected animal is modeled using dispersion theory for a homogeneous turbulent airflow. The concentration and size distribution of the evaporating droplets in the resulting “Gaussian breath plume” are calculated as functions of position, humidity, and temperature. The overall transmission probability is modeled with a combination of the time-dependent viral concentration in the infected animal and the probability of droplet inhalation by the exposed animal downstream. We demonstrate that the breath plume model is broadly consistent with the results of Lowen <em>et al.,</em> without invoking airborne virus survivability. The results also suggest that, at least for guinea pigs, variation in viral kinetics within the infected animals is the dominant factor explaining the increased transmission probability observed at lower temperatures.</p> </div