Inclusion

1. Written informed consent must be obtained from the patient or his/her legal guardian.
2. 18 years of age or older
3. Current disease duration ≤ 7 days.
4. Temperature ≥ 37.8°C (100°F) (any body site, any measurement device, including self-reported) or tactile fever, either of them noted at least once within the last 7 days.
5. Clinical suspicion of bacterial or viral LRTI: At least one of the following respiratory signs or symptoms:
   1. cough (new or worsening)
   2. sputum production
   3. Dyspnea
   4. shortness of breath
   5. Chest discomfort
   6. wheezing, rhonchi

Exclusion

1. Systemic antibiotics within 72 hours prior to ED/UCC presentation
2. Suspicion and/or confirmed diagnosis of infectious gastroenteritis/colitis
3. Inflammatory disease (e.g., IBD, SLE, RA, Kawasaki, other vasculitis)
4. Congenital immune deficiency (CID)
5. A proven or suspected infection on presentation with Mycobacterial (e.g., MAC, MABC), parasitic or fungal (e.g., Candida, Histoplasma, Aspergillus) pathogen
6. HIV, HBV, or HCV infection (self-declared or known from medical records)
7. Major trauma and\or burns in the last 7 days
8. Major surgery in the last 7 days
9. Pregnancy- self reported or medically confirmed
10. Active malignancy - Cancer diagnosed within the previous six months, recurrent, regionally advanced or metastatic cancer, cancer for which treatment had been administered within six months, or hematological cancer that is not in complete remission.
11. Current treatment with immune-suppressive or immune-modulating therapies, at some point in the past 10 days, including without limitations:
    • Administration of PO\IV\IM high dose steroids >1mg/kg/day prednisone (or equivalent) at some point in the past 10 days or daily continuous use of steroids > 0.25 mg/kg/day in the past 7 days
    • Monoclonal antibodies, anti-TNF agents
    • Intravenous immunoglobulin (IVIG)
    •  Cyclosporine, Cyclophosphamide, Tacrolimus, Azathioprine, Methotrexate G/GM-CSF, Interferons
12.  Considered unsuitable for the study by the study team