Impact of Emergency Department Probiotic (LGG) Treatment of Pediatric Gastroenteritis

Inclusion Criteria: 1. Age 3-48 months (have not yet reached their fourth birthday); AND 2. Presence of 3 or more watery stools within 24 hours of screening; AND 3. Duration of vomiting or diarrhea less than 7 days; AND 4. Symptoms consistent with acute intestinal infectious process. Exclusion Criteria: 1. Presence of an indwelling vascular access line; OR 2. Presence of structural heart disease excluding non-pathological heart murmurs; OR 3. Receiving immunosuppressive therapy or history of immunodeficiency; OR 4. Hematochezia in the preceding 48 hours; OR 5. Chronic gastrointestinal problems (e.g. short gut syndrome, inflammatory bowel disease); OR 6. Patients with known pancreatitis; OR 7. History of abdominal surgery; OR 8. Critically ill patients; OR 9. Family member with an indwelling vascular access line, or on immunosuppressive therapy, or with a known immunodeficiency; OR 10. Bilious emesis; OR 11. Probiotic use (supplement) in the preceding 2 weeks; OR 12. Oral or intravenous steroid use in the preceding six months; OR 13. Previously enrolled in this trial; OR 14. Allergy to lactobacillus or Microcrystalline Cellulose (MCC); OR 15. Allergy to erythromycin, clindamycin, AND betalactam antibiotics (all); OR 16. Not available for daily follow-up while symptomatic; OR 17. Parent/guardian not speaking English or Spanish; OR 18. Under 6 months old AND premature (\<37 weeks).