First evidence of West Nile virus amplification and relationship to human infections

The spatio-temporal relationship between unusual sightings of dead birds and human West Nile virus infections has been observed in many studies and has been proposed as an indicator of an intense amplification cycle between birds and mosquitoes. However, to date, no single study has provided quantitative evidence that the amplification cycle occurs at the local level and that it operates within certain temporal parameters. Here, we use a novel geostatistical and spatial analytic methodology and present the first evidence that the localized unusual space-time correspondence of dead birds models the amplification cycle and that this cycle peaks 15-16 days prior to human onset of West Nile virus infections. During the process of establishing this relationship, we extend the traditional Knox space-time interaction measure to overcome pair-dependency limitations and use a novel implementation of the kappa non-chance agreement measure to identify the temporal characteristics of the association of bird deaths to human West Nile infections.