2.1.1. Outbreak of H7N1 in Italy in 1999/2000 Northern Italy has experienced a number of avian influenza outbreaks from 1997 onwards [6] [7] [8] [9] [10] . These all occurred in an extremely dense poultry production area (up to 70 000 birds/km 2 ) and involved a significant number of farms keeping turkeys, a species known from experimental studies to be highly susceptible to avian influenza [11] . Furthermore, in this region there are many wetlands and resting sites for migratory waterfowl in close proximity to the poultry industry, which likely lead to multiple introductions from the wild bird host.