Mass deworming (also called preventive chemotherapy) is the process of treating large numbers of people, particularly children, for helminthiasis (for example soil-transmitted helminths (STH)) and schistosomiasis infections in areas with a high prevalence of these conditions. It involves treating everyone – often all children who attend schools, using existing infrastructure to save money – rather than testing first and then only treating selectively. Serious side effects have not been reported when administering the medication to those without worms, and testing for the infection is many times more expensive than treating it. So for the same amount of money, mass deworming can treat more people more cost-effectively than selective deworming. Mass deworming is one example of mass drug admi