Spatial relationships in the Q fever outbreaks 2007-2010 in the Netherlands

We analyzed the Q fever epidemic in the Netherlands on a national scale from a spatial point of view. Data on dairy goat farms and Dutch population, whether or not infected, were geo-referenced. Human cases were counted in GIS at different distance classes for all dairy goat farms, farms with Q fever based on BTM analysis, and farms with clinical symptoms. In all selections, human incidence decreased with increasing distances from dairy goat farms. Incidence was highest around farms with clinical symptoms. Depending on the acceptable incidence value, a dairy goat-free zone around residential areas could be defined. Cluster analyses were performed to identify local clusters of both infected farms and human cases and to identify focused clusters of human cases. Focused clusters were detected for only 14 out of 29 farms with clinical symptoms, giving rise to a new hypothesis on the transmission of Q fever.