Abstract:
When an exotic infectious disease invades a susceptible environment, protection
zones are enforced. Historically, such zones have been shaped as circles of
equal radius (ER), centred on the location of infected premises. Because the ER
policy seems to assume that epidemic dissemination is driven by a similar
number of secondary cases generated per primary case, it does not consider
whether local features, such as connectivity, influence epidemic dispersal. Here
we explored the efficacy of ER protection zones. By generating a geographically
explicit scenario that mimicked an actual epidemic, we created protection
zones of different geometry, comparing the cost-benefit estimates of ER protection
zones to a set of alternatives, which considered a pre-existing connecting
network (CN) – the road network. The hypothesis of similar number of cases
per ER circle was not substantiated: the number of units at risk per circle differed
up to four times among ER circles. Findings also showed that even a
small area (of <115 km2) revealed network properties. Because the CN policy
required 20% less area to be protected than the ER policy, and the CN-based
protection zone included a 23.8% greater density of units at risk/km2 than the
ER-based alternative, findings supported the view that protection zones are
likely to be less costly and more effective if they consider connecting structures,
such as road, railroad and/or river networks. The analysis of local geographical
factors (contacts, vectors and connectivity) may optimize the efficacy of control
measures against epidemics.
