Have cases of West Nile virus disease been reported in every state of the continental US?

West Nile virus disease has indeed been reported in every state of the continental United States. This widespread occurrence is a result of the virus's ability to be transmitted by various mosquito species, which are present across different regions. The factors contributing to its prevalence include the adaptability of the mosquitoes to various climates and habitats, alongside the presence of migratory bird populations that serve as reservoirs for the virus.

While the disease has been reported in all states, the incidence rates can vary significantly between regions based on environmental conditions and local mosquito populations. Furthermore, it is important to note that although cases can occur anywhere, the concentration and frequency of reported cases tend to be higher in certain areas, particularly those with abundant standing water where mosquitoes breed more readily.

The other options do not capture the full extent of West Nile virus disease's reach across the continental U.S. Therefore, acknowledging that cases have been documented in all states provides a more accurate understanding of the public health implications surrounding this vector-borne illness.