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
