Transmission parameters of highly pathogenic avian influenza (H7N1) among industrial poultry farms in northern Italy in 1999-2000.

We estimated between-flock transmission parameters of the highly pathogenic avian influenza (HPAI) epidemic that struck the poultry industry of northern Italy (including turkeys, layer hens, broilers, gamebirds, and waterfowls) from December1999 through April 2000. The average number of susceptible flocks that were infected with HPAI virus by each infectious flock during a day, beta, was estimated using a generalised linear model (GLM). The HPAI’s reproductive ratio (Rh)—the average number of new cases that were caused by an infectious flock, was subsequently obtained for the regions of Lombardy and Veneto, where 382 out of 413 (92.5%) of infected premises were located. In both regions, Rh decreased to ~ 1 during the second month of the epidemic showing that its containment had been initiated. Subsequently, during the last two months of the epidemic, beta and Rh were reduced to 0.04/day and 0.6, respectively, in Veneto and to 0.07/day and 0.8 in Lombardy. The reduction of the susceptible population through strict control measures, including pre-emptive slaughter of at-risk poultry flocks, was implemented to a greatest extent in Veneto and this might have been associated with a more rapid control of the epidemic in this region than in Lombardy.