Outbreaks of coinfections: the critical role of cooperativity

TL;DR

This paper introduces a mean field SIR model that explicitly incorporates cooperative coinfection effects, revealing various phase transition behaviors including continuous and discontinuous outbreaks of multiple diseases.

Contribution

The study presents a novel SIR model accounting for cooperative coinfection, highlighting complex epidemic thresholds and transition types not previously characterized.

Findings

Cooperative coinfection leads to diverse epidemic thresholds.

Both continuous and discontinuous phase transitions are observed.

Results are derived from a mean field model and are expected to be broadly applicable.

Abstract

Modeling epidemic dynamics plays an important role in studying how diseases spread, predicting their future course, and designing strategies to control them. In this letter, we introduce a model of SIR (susceptible-infected-removed) type which explicitly incorporates the effect of {\it cooperative coinfection}. More precisely, each individual can get infected by two different diseases, and an individual already infected with one disease has an increased probability to get infected by the other. Depending on the amount of this increase, we observe different threshold scenarios. Apart from the standard continuous phase transition for single disease outbreaks, we observe continuous transitions where both diseases must coexist, but also discontinuous transitions are observed, where a finite fraction of the population is already affected by both diseases at the threshold. All our results are obtained in a mean field model using rate equations, but we argue that they should hold also in more general frameworks.