Because outbreaks have occurred from Washington state to New York state, campers and backpackers should avoid drinking any untreated water from mountain streams. Giardiasis affects three times more children than adults, particularly diapered children and toddlers being toilet-trained. Families with young children who attend day-care centers are at greater risk of developing giardiasis than is the general population. The usual interval between infection and the onset of acute symptoms ranges from one to two weeks. Upper gastrointestinal symptoms such as vomiting may predominate.
Fever is unusual.
Many infected people, however, have very mild symptoms or no symptoms at all. Blood or mucus in the stool rarely occurs. Diagnosis Giardiasis is sometimes overlooked because the symptoms are similar to other gastrointestinal diseases, and because many physicians are unfamiliar with parasitic diseases. Stool specimens should be collected and examined over a period of at least three days. It is sometimes necessary to collect samples for four to five weeks.