This study is a prospective observational clinical study in the emergency department, inpatient ward, intensive care unit, and outpatient department of the Angkor Hospital for Children in Siem Reap, Cambodia. Study subjects will include children 16 years or less, who present during the annual Dengue Fever outbreak with suspected Dengue fever. Subjects include children with an acute febrile illness, and two of the following: headache, retro-orbital pain, myalgias, arthralgia, rash, hemorrhagic manifestations, or plasma leakage (i.e. shortness of breath, abdominal distention/pain). Clinicians will determine their clinical suspicion of dengue, intended therapeutic interventions and disposition following a history and physical exam but before ultrasound imaging. Study personnel will perform diagnostic bedside ultrasound imaging of the gallbladder and peritoneal and pleural spaces (FAST exam) and the clinician again determine their clinical suspicion of Dengue, intended therapeutic interventions and disposition. Patients will be followed to determine clinical outcome, therapeutic interventions and disposition. The primary endpoint is progression of disease. The secondary endpoint will be change in clinical care provided in the emergency department related to ultrasound imaging.