Contaminated food is a less common etiology. Endemic infection occurs most commonly from July through October among children younger than 5 years and adults aged 25-39 years. Morbidity is moderate and involves primary GI symptoms. It can have high carrier rates within Native American populations residing on reservations. The majority of patients experience a more insidious onset of symptoms, which are recurrent or resistant.
Stools become malodorous, mushy, and greasy.
Watery diarrhea may alternate with soft stools or even constipation. Stools do not contain blood or pus because dysenteric symptoms are not a feature of giardiasis. Upper GI symptoms, often exacerbated by eating, accompany stool changes or may be present in the absence of soft stools. These include upper and midabdominal cramping, nausea, early satiety, bloating, sulfurous belching, substernal burning, and acid indigestion. Constitutional symptoms Anorexia, fatigue, malaise, and weight loss are common.