Immune Responses to Dengue and Sepsis

The goal of this research study is to help the investigators better understand serious dengue disease. The investigators will collect clinical information and up to four blood samples from participants with dengue, influenza, sepsis, or healthy people. The investigators will perform multiple analyses on the blood samples and compare results between dengue patients and those with influenza or sepsis and healthy people.

Inclusion Criteria: * Patients with dengue-like illness: Patients presenting with dengue-like symptoms for a duration of maximum 72h before inclusion. Dengue-like symptoms include: presentation with oral temperature \>38°C AND at least two of the following symptoms suggestive of dengue-like illness: headache, retro-orbital pain, myalgia, joint pain, rash, any bleeding symptoms, nausea or vomiting, lethargy or restlessness , abdominal pain, liver enlargement \- Influenza patients: Patients presenting with with oral temperature \>38°C and cough that started within the last 4 days AND rapid test or PCR positive for influenza infection AND no COVID-19 or positive bacterial cultures at the time of enrollment. * Sepsis patients: Patients admitted for less than 48 hours with a primary diagnosis of sepsis as per treating team AND have blood cultures ordered AND on empiric antibiotics due to concern for bacterial infection. * Healthy controls: Participants with no chronic illness, no regular medications, no febrile illness in 28 days, no diagnosis of or treatment for dengue or bacterial infection in the past 6 months. Exclusion Criteria: * For biobanking purposes, children less than 2 years of age, and individuals who are pregnant, pregnant within the last 90 days, and/or breastfeeding are excluded due to restrictions on the blood volumes and the repeated sampling times. * Individuals that do not provide informed consent will not be included for the study. * Severe/chronic/recurrent pathological conditions: clinically significant autoimmune disease or immunodeficiency (including history of organ transplant), haematologic disorders, cardiac diseases, diabetes, cancer, HIV, chronic hepatic or renal insufficiency. * Chronic administration (defined as more than 14 days) of immunosuppressants or other immune-modifying drugs within the 6 months prior to the inclusion. For corticosteroids, this will mean a dose equivalent to 20 mg/day of prednisone or equivalent for \> 2 weeks (inhaled and topical steroids allowed) * Chronic administration of NSAIDs, including aspirin: prolonged intake (\>2 weeks) within 6 months before study or any intake within the 7 days preceding sampling \[exception for low dose aspirin: maximum 250mg/daily\] * Any underlying, chronic, or current condition that, in the opinion of the investigator, may interfere with their participation in the study. * Expected death in the next 48-hours