Within-flock transmission of H7N1 highly pathogenic avian influenza virus in turkeys during the Italian epidemic in 1999-2000.

Highly pathogenic avian influenza (HPAI) viruses show different disease dynamics between virus strains and host species, and therefore epidemic field data are very valuable. This study used field data of the HPAI H7N1 epidemic which affected Northern Italy in 1999-2000. Field mortality data was back-calculated into a S-I-format to estimate the transmission rate parameter beta, indicating the number of birds infected per infectious bird per time unit. The bird-infectious period was assumed to be 2 days, and all birds were assumed to die after this infectious period. The estimated beta for HPAI H7N1 virus transmission in turkeys was 1.43 (95% CI: 1.17-1.74). Farm risk factors such as flock size and age of the turkeys did not influence the estimated transmission rate parameter.