To the Editor.
—In response to numerous waterborne outbreaks of cryptosporidiosis, including 1 in Milwaukee in 1993 that affected an estimated 403 000 persons,1 the Centers for Disease Control and Prevention (CDC), in collaboration with other federal agencies, state and local health departments, and other interested parties, formed the Working Group on Waterborne Cryptosporidiosis (WGWC). One of the WGWC's objectives has been to develop guidelines for water utilities, health departments, and others about how to prepare for and respond to future waterborne outbreaks. The WGWC's guidelines for microbiology laboratories have been published,2 and although they are directed at laboratory professionals, the guidelines have important implications for clinicians as well.The WGWC recognized that an obstacle to the early detection of outbreaks of cryptosporidiosis was poor communication between microbiology laboratories and health care professionals. Clinicians often make the erroneous assumption that a request for ova and parasite testing includes