Acknowledgments Introduction Case 1 Emma, a 16-month-old Girl With Vomiting and Diarrhea Case 2 Anita, a 4-month-old Girl With Respiratory Distress Case 3 Baby Girl Smith, a Newborn With Respiratory Distress Case 4 Parker, a 3-year-old Boy With Difficulty Breathing Case 5 John, a 4-day-old Boy With Hyperbilirubinemia Case 6 Isaiah, an 8-year-old Boy With Shortness of Breath Case 7 Rose, a 3-week-old Girl With Fever Case 8 Austin, an 8-month-old Boy With Fever and Vomiting Case 9 Holly, a 5-year-old Girl With Fever, Vomiting, and Thigh Swelling Case 10 Ilyas, a 6-year-old Boy With Acute Abdominal Pain Case 11 Judah, a 2-year-old Boy With Buttock Pain and Redness Case 12 Maryam, a 4-year-old Girl With Fever and Cough Case 13 Freddy, a 9-week-old Boy With an Episode of Decreased Responsiveness Case 14 Brian, a 2-year-old Boy With Fussiness and Fever Case 15 Liam, a 6-week-old Infant With Poor Weight Gain Case 16 Simon, a 15-month-old Boy With Abnormal Movements and Fever Case 17 Polly, a 16-year-old Girl With Fever, Abdominal Pain, and Vomiting Case 18 Payton, a 14-year-old Boy With Throat Pain and Fever Case 19 Ida, a 15-month-old Girl With Pallor and Fatigue Case 20 Jenny, a 14-year-old Girl With a Severe Headache Case 21 Katelyn, a 4-year-old Girl With Fever and Neck Swelling Case 22 Taj, a 12-year-old Boy With Hyperglycemia Case 23 Finn, a 2-year-old Boy With Fever and Leg Pain Case 24 Aubree, a 15-year-old Girl With Recurrent Abdominal Pain Case 25 Andy, a 9-year-old Boy With Respiratory Distress and Vomiting Case 26 Janice, an 11-year-old Girl With Prolonged Menses Case 27 Amaia, a 16-year-old Girl With Hematemesis Case 28 Chandler, a 7-year-old Boy With Eye Swelling Case 29 Philip, a 7-year-old Boy With Intermittent Abdominal Pain Case 30 Alex, a 9-year-old Boy With Edema and Hematuria Case 31 Ella, an 8-year-old Girl With 2 Weeks of Fever Case 32 Maria, a 15-year-old Girl With Lower Extremity Weakness Case 33 Juan, a 16-year-old Boy With Shoulder Pain Case 34 Bernard, a 15-year-old Boy With Abdominal Pain and Diarrhea Case 35 Ricky, a 3-year-old Boy With Shaking Case 36 Alberto, a 7-year-old Boy With Edema Case 37 Reese, a 12-year-old Girl With Weight Loss Case 38 Lily, a 6-month-old Girl With Fever and Lethargy Case 39 Isla, a 15-month-old Girl With Fever and Rash Case 40 Rena, a 14-year-old Girl With Abdominal Pain and Vomiting Case 41 Malik, a 24-month-old Boy With Pneumonia and Persistent Fever Case 42 Flora, an 8-year-old Girl With Worsening Epigastric Pain and Emesis Case 43 Scott, a 3-year-old Boy With Bloody Diarrhea and Decreased Urination Case 44 Lucy, a 16-year-old Girl With Altered Mental Status Case 45 Sam, a 10-month-old Boy With Hypoglycemia Case 46 Makayla, a 16-year-old Girl With Fever and Blurry Vision Case 47 Olive, a 4-month-old Girl With Lethargy and Hyponatremia Case 48 Aria, a 16-year-old Girl With Headache and Confusion Case 49 Tomás, a 17-month-old Boy With Worsening Respiratory Status Case 50 Anna, an 11-year-old Girl With Medical Complexity, Fever, Increased Secretions, and Increased Seizure Frequency Appendix Index.