To the Editor.
—The article by Drs Shaw and Stevens1 about reactive arthritis in a patient with giardiasis perpetuates the common misconception that "contaminated well water" is the usual source of Giardia infection in the United States. While fecally contaminated well water is occasionally implicated, 90% of infections are acquired by drinking unfiltered surface water (usually municipal drinking water from streams or rivers) or from diaper-aged children who attend day-care centers. Chlorinated municipal drinking water that meets standards for coliform bacteria can still transmit Giardia if the process for water treatment does not include filtration. At present, 36 to 40 million Americans live in communities, primarily in mountainous regions, that are supplied by unfiltered surface water. In addition, many people visit these areas during summer and winter vacations.Many physicians are still unaware of the high rate of Giardia infection among children who attend day-care centers. Based on telephone