The most appropriate management is stool testing for ova and parasites. Infectious causes of chronic diarrhea are uncommon in immunocompetent adults in developed countries, except for infection with Giardia lamblia. Giardiasis should be considered in patients with exposure to young children or potentially contaminated water such as lakes and streams. Infection is asymptomatic in more than 50% of patients, and the protozoa clear spontaneously. In the remaining patients, symptoms typically occur 1 to 2 weeks after infection and include watery, foul-smelling diarrhea; bloating; flatulence; and belching. Significant weight loss is common because of anorexia and malabsorption, but fever is distinctly unusual. Gastrointestinal symptoms can persist for several weeks to months in the absence of treatment. Patients with hypogammaglobulinemia are at increased risk of developing severe or chronic infection. Given this patient's profession as a day care worker, she is at risk for exposure to a number of infectious causes of diarrhea. The duration of her diarrhea, as well as the associated bloating and weight loss, are more consistent with giardiasis than a bacterial infection. Therefore, an assessment of this patient's stools for ova and parasites would be more appropriate than stool cultures.

A colonoscopy is not indicated at this time because this patient is otherwise healthy and does not have gastrointestinal bleeding or signs suggesting inflammatory bowel disease, such as blood in the stool.

Given the chronic nature of this patient's symptoms and her associated weight loss, avoiding further testing would not be appropriate. Her symptoms warrant evaluation with stool testing.