Prognostic epidemiological indices and the fate of ongoing infectious disease outbreaks

Prognostic indices, such as the reproduction number or the epidemicity index, help assess the fate of ongoing infectious disease epidemics. While the first is of established importance, the latter focuses on the instantaneous reactivity of the infective compartment to new flare-ups. When subthreshold values of such indices apply (respectively, below the unity for the first and below zero for the latter), they warrant long-term disease-free and unreactive epidemiological conditions. 

These prognostic indicators benefit policymakers during the assessment and implementation of containment measures to reduce the disease burden. They may depend on an array of factors, including environmental forcings and the effect of containment measures on disease transmission.

We showcase a possible implementation of such prognostic indices with reference to the disastrous 2010-2019 Haiti cholera outbreak. To this end, we use a compartmental model that considers rainfalls as an environmental forcing and societal actions tackling the disease's spread. We thus test several scenarios considering a different deployment of intervention measures and we evaluate the outcome of the evolution of the prognostic indices and the epidemiological trajectory in the Haitian regions. We find that subthreshold values of these indices lead to faster waning-disease conditions.
As these indices can recap diverse epidemiological signatures induced by the spatial and temporal deployment of containment measures and potentially by evolving environmental forcings, their implementation could enable policymakers to strategically adopt containment measures in response to both evolving epidemiological and climate forcings.