“The incidence of dengue has grown dramatically around the world in recent decades,” the WHO writes in an updated fact sheet about dengue and severe dengue published on the organization’s website. According to the fact sheet, “Over 2.5 billion people — over 40 percent of the world’s population — are now at risk from dengue,” and “WHO currently estimates there may be 50-100 million dengue infections worldwide every year” (January 2012).