Risk factors for highly pathogenic H7N1 avian influenza virus infection in poultry during the 1999–2000 epidemic in Italy Luca Busani a,b, * , Maria Grazia Valsecchi c , Emanuela Rossi c , Marica Toson a , Nicola Ferre ` a , Manuela Dalla Pozza a , Stefano Marangon a a Istituto Zooprofilattico delle Venezie, viale dell’Universita ` 10, 35020 Legnaro, Padova, Italy b Istituto Superiore di Sanita ` , viale Regina Elena, 299, 00161 Rome, Italy c Unit of Medical Statistics, Department of Clinical Medicine and Prevention, University of Milano-Bicocca, Via Cadore 48, 20052 Monza, Italy Accepted 13 February 2008 Abstract In 1999–2000, Italian poultry production was disrupted by an H7N1 virus subtype epidemic of highly pathogenic avian influenza (HPAI). The objectives of the present study were to identify risk factors for infection on poultry farms located in regions that had the highest number of outbreaks (Veneto and Lombardia) and the impact of pre-emptive culling as a complementary measure for erad- icating infection. A Cox regression model that included spatial factors, such as the G index, was used. The results confirmed the rela- tionship between risk of infection and poultry species, production type and size of farms. The effectiveness of pre-emptive culling was confirmed. An increased risk of infection was observed for poultry farms located near an infected farm and those at altitudes less than 150 m above sea level. The measures for the control and eradication of AI virus infection need to consider species differences in suscep- tibility, the types of production and the density of poultry farms in the affected areas. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Avian influenza; Poultry; Epidemiology; Survival analysis; Risk factors Introduction In 1999–2000, Italy experienced an epidemic of highly pathogenic avian influenza (HPAI) in industrial poultry population. The epidemic was caused by an H7N1 subtype, which had been circulating in the area as a low pathogenicity avian influenza (LPAI) virus since March 1999 and began to spread rapidly in December 1999, after having mutated into HPAI virus (Capua and Marangon, 2000). The evolution of LPAI viruses of the H5 and H7 subtypes circulating in a domestic poultry population has been described in other countries, such as the United States (Pennsylvania) and Mexico (Bean et al., 1985; Garcia et al., 1996). To contain the epidemic and eradicate infection, all measures provided for by EU legislation were applied from 17th December 1999, including culling at infected premises (IP), prohibiting the restocking of poultry farms and restricting the movement of live poultry, vehicles and per- sonnel in the areas at risk (CEC, 1992). Moreover, pre- emptive culling was carried out on poultry farms located near an IP, those that had at risk contacts with an IP and those that belonged to the owner as the IP. Further- more, to monitor infection in the affected regions, intensive surveillance was implemented. Despite these eradication measures, the infection spread to 413 poultry farms; as a result, approximately 16 million birds died or were culled in infected or at risk farms and an estimated 110 million Euros in compensation were paid to farmers (Marangon et al., 2005). The areas most affected by the epidemic were the regions of Lombardia and Veneto in North-Eastern Italy, where 382/413 (92.5%) outbreaks 1090-0233/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.tvjl.2008.02.013 * Corresponding author. Address: Istituto Zooprofilattico delle Venezie, viale dell’Universita ` 10, 35020 Legnaro, Padova, Italy. Tel.: +39 049 8084332; fax: +39 049 8830268. E-mail address: crev.lbusani@izsvenezie.it (L. Busani). www.elsevier.com/locate/tvjl Available online at www.sciencedirect.com The Veterinary Journal xxx (2008) xxx–xxx The Veterinary Journal ARTICLE IN PRESS Please cite this article in press as: Busani, L., et al., Risk factors for highly pathogenic H7N1 avian influenza virus ..., The Veterinary Journal (2008), doi:10.1016/j.tvjl.2008.02.013