Identifying West Nile virus risk areas: the Dynamic Continuous-Area Space-Time system.

The Dynamic Continuous-Area Space-Time (DYCAST) system was developed to identify and prospectively monitor high-risk areas for West Nile virus in New York, New York (New York City). The system is based on a geographic model that uses a localized Knox test to capture the nonrandom space-time interaction of dead birds, as an indicator of an intense West Nile virus amplification cycle, within a 1.5-mile (2.41-km) buffer area and 21-day moving window. The Knox analysis is implemented as an interpolation function to create a surface of probabilities over a grid of 1,400 cells overlaying New York City. The model's parameters were calibrated using year 2000 data and information on the vector-host transmission cycle. The DYCAST system was implemented in a geographic information system and used operationally in year 2001. It successfully identified areas of high risk for human West Nile virus infection in areas where five of seven human cases resided, at least 13 days prior to the onset of illness, and proved that it can be used as an effective tool for targeting remediation and control efforts.