An environmental determinant of viral respiratory disease

Abstract

The evident seasonality of influenza suggests a significant role for weather and climate as one of several determinants of viral respiratory disease (VRD), including social determinants which play a major role in shaping these phenomena. Based on the current mechanistic understanding of how VRDs are transmitted by small droplets, we identify an environmental variable, Air Drying Capacity (ADC), as an atmospheric state-variable with significant and direct relevance to the transmission of VRD. ADC dictates the evolution and fate of droplets under given temperature and humidity conditions. The definition of this variable is rooted in the Maxwell theory of droplet evolution via coupled heat and mass transfer between droplets and the surrounding environment. We present the climatology of ADC, and compare its observed distribution in space and time to the observed prevalence of influenza and COVID-19 from extensive global data sets. Globally, large ADC values appear to significantly constrain the observed transmission and spread of VRD, consistent with the significant coherency of the observed seasonal cycles of ADC and influenza. Our results introduce a new environmental determinant, rooted in the mechanism of VRD transmission, with potential implications for explaining seasonality of influenza, and for describing how environmental conditions may impact to some degree the evolution of similar VRDs, such as COVID-19.

On the Environmental Determinants of COVID-19 Seasonality

“…High UV and high ADC linked to lower prevalence, and vice-versa, although this relationship is weak over a certain period in autumn over India. This result is in line with the expected effect of these two variables on the survival and transmissibility of SARS-Cov-2 (e.g., Choi et al, 2020; Seyer and Sanlidag, 2020; Schuit et al, 2020; Ratnesar-Shumate et al, 2020). The case of India in particular is quite striking, especially since the country attracted much attention due to the explosiveness of its COVID-19 outbreak and its different timing of peak incidence (e.g., Bherwani et al, 2020) compared to those in temperate regions.…”

“…High UV and high ADC linked to lower prevalence, and vice-versa, although this relationship is weak over a certain period in autumn over India. This result is in line with the expected effect of these two variables on the survival and transmissibility of SARS-Cov-2 (e.g., Choi et al, 2020;Seyer and Sanlidag, 2020;Schuit et al, 2020;Ratnesar-Shumate et al, 2020).…”

“…Through extensive country-level data spanning the 1-year pandemic period, this study evaluates and compares the role of four environmental variables (temperature, humidity, ADC, and UV) with the potential to influence the spread of COVID-19. Three important results that emerge from this study are that: (1) the spread and prevalence of COVID-19 appears to display some seasonality consistent, to some extent, with the seasonality of the analyzed environmental variables and their known relationships to influenza seasonality; (2) two environmental variables in particular, ADC and UV, evolve consistently with COVID-19 spread across the selected countries of all climates and at both the weekly and the seasonal timescales, and their relationship to COVID-19 spread is consistent with their respective effects on the fate of respiratory droplets (ADC, Choi et al 2020) and on virus survival (UV, Seyer and Sanlidag, 2020;Schuit et al, 2020;Ratnesar-Shumate et al, 2020). Therefore, ADC and UV may provide the basis for a physically-based framework shaping seasonal variations in COVID-19 prevalence across the world; and (3) we also find that, as was the case for influenza, absolute humidity and temperature do not exhibit a consistent relationship to COVID-19 cases across all climate zones.…”

“…The prevalence of COVID-19 tends to exhibit a distinct seasonality in the five representative countries (see Section 2.1 for a selection of countries), similar to that of influenza ( Figs. 1 and S2; Tamerius et al, 2011;2013;Choi et al, 2020). For example, temperate countries in both hemispheres (i.e., Canada, Germany, and Chile) experienced peak COVID-19 incidence .…”

“…where T a is the ambient temperature, RH the ambient relative humidity, L v the latent heat of vaporisation, R v the specific gas constant for water vapour, ρ liquid water density, K the thermal conductivity of air, e s the saturation vapor pressure at temperature, D is the diffusion coefficient of water vapour. More details can be found in Choi et al (2020).…”