Perspectives on the basic reproductive ratio

Abstract

The basic reproductive ratio, R ₀ , is defined as the expected number of secondary infections arising from a single individual during his or her entire infectious period, in a population of susceptibles. This concept is fundamental to the study of epidemiology and within-host pathogen dynamics. Most importantly, R ₀ often serves as a threshold parameter that predicts whether an infection will spread. Related parameters which share this threshold behaviour, however, may or may not give the true value of R ₀ . In this paper we give a brief overview of common methods of formulating R ₀ and surrogate threshold parameters from deterministic, non-structured models. We also review common means of estimating R ₀ from epidemiological data. Finally, we survey the recent use of R ₀ in assessing emerging diseases, such as severe acute respiratory syndrome and avian influenza, a number of recent livestock diseases, and vector-borne diseases malaria, dengue and West Nile virus.