This 2021 season the District is utilizing West Nile virus risk surface maps created by VectorSurv, a collaboration between the Mosquito and Vector Control Association of California, the California Department of Public Health, and the Davis Arbovirus Reasearch and Training Lab at UC Davis. These maps incorporate environmental conditions and mosquito and disease surveillance data submitted by local districts into a statewide database. A risk assessment model combines these variables to show color-coded areas of various risk for each week of the year on a map.

The factors used to calculate risk are temperature, mosquito abundance, WNV positive mosquito pools, WNV infected sentinel chickens, and WNV positive dead birds. These values are combined to derive an overall risk level. The overall risk falls into three categories: normal season (yellow), emergency planning (orange), and epidemic (red). The map shows the levels of overall risk by color, as long as there is sufficient data for the area. The map updates weekly to incorporate the latest data.

These maps can inform District staff about areas of the County that are more likely to have West Nile virus activity. With this knowledge, additional surveillance can be conducted in specific locations that have higher overall risk. It also provides and indication to the District operations department when enhanced mosquito control activities might be needed.