  We use a stochastic metapopulation model to study the combined effects of
seasonality and spatial heterogeneity on disease persistence. We find a
pronounced effect of enhanced persistence associated with strong heterogeneity,
intermediate coupling strength and moderate seasonal forcing. Analytic
calculations show that this effect is not related with the phase lag between
epidemic bursts in different patches, but rather with the linear stability
properties of the attractor that describes the steady state of the system in
the large population limit.
