Spatial interference between infectious hotspots: epidemic condensation and optimal windspeed

TL;DR

This paper investigates how wind speed influences the spread of infections between two hotspots, revealing complex effects including optimal wind speeds for minimizing infection peaks and the phenomenon of epidemic condensation.

Contribution

It introduces the concept of epidemic condensation and analyzes the non-monotonic relationship between wind speed and infection peaks based on hotspot infectivity ratios.

Findings

Increasing wind speed reduces infection peaks when upstream hotspot is less contagious.

An optimal wind speed exists for certain infectivity ratios, minimizing infection peaks.

Beyond a critical infectivity ratio, wind speed no longer benefits containment.

Abstract

We discuss the effects of spatial interference between two infectious hotspots as a function of the mobility of individuals (wind speed) between the two and their relative degree of infectivity. As long as the upstream hotspot is less contagious than the downstream one, increasing the wind speed leads to a monotonic decrease of the infection peak in the downstream hotspot. Once the upstream hotspot becomes about between twice and five times more infectious than the downstream one, an optimal wind speed emerges, whereby a local minimum peak intensity is attained in the downstream hotspot, along with a local maximum beyond which the beneficial effect of the wind is restored. Since this non-monotonic trend is reminiscent of the equation of state of non-ideal f luids, we dub the above phenomena epidemic condensation. When the relative infectivity of the upstream hotspot exceeds about a factor five, the beneficial effect of the wind above the optimal speed is completely lost: any wind speed above the optimal one leads to a higher infection peak. It is also found that spatial correlation between the two hotspots decay much more slowly than their inverse distance. It is hoped that the above findings may offer a qualitative clue for optimal confinement policies between different cities and urban agglomerates.