title: Quasi-neutral theory of epidemic outbreaks.
abstract: Some epidemics have been empirically observed to exhibit outbreaks of all possible sizes, i.e., to be scale-free or scale-invariant. Different explanations for this finding have been put forward; among them there is a model for "accidental pathogens" which leads to power-law distributed outbreaks without apparent need of parameter fine tuning. This model has been claimed to be related to self-organized criticality, and its critical properties have been conjectured to be related to directed percolation. Instead, we show that this is a (quasi) neutral model, analogous to those used in Population Genetics and Ecology, with the same critical behavior as the voter-model, i.e. the theory of accidental pathogens is a (quasi)-neutral theory. This analogy allows us to explain all the system phenomenology, including generic scale invariance and the associated scaling exponents, in a parsimonious and simple way.
authors.affiliation: Departamento de Física, Instituto de Física Aplicada, Universidad Nacional de San Luis-CONICET, San Luis, Argentina.
authors.forename: Oscar A
authors.initials: OA
authors.lastname: Pinto
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Muñoz
mesh_terms: D058872:Epidemics; D006801:Humans; D008954:Models, Biological; D013997:Time Factors