  In this paper, we show that many structured epidemic models may be described
using a straightforward product structure. Such products, derived from products
of directed graphs, may represent useful refinements including geographic and
demographic structure, age structure, gender, risk groups, or immunity status.
Extension to multi-strain dynamics, i.e. pathogen heterogeneity, is also shown
to be feasible in this framework. Systematic use of such products may aid in
model development and exploration, can yield insight, and could form the basis
of a systematic approach to numerical structural sensitivity analysis.

Populations and Evolution;Quantitative Methods