Intervention: Oseltamivir
Trial phase: Phase 4
ATC code: J05AH02
SMILES: CCOC(=O)C1=C[C@@H](OC(CC)CC)[C@H](NC(C)=O)[C@@H](N)C1
Sex: All
Age groups: Adult | Older Adult
Healthy volunteers: No
Participants at risk: 84
Group description: Subjects randomized to the oral treatment arm will receive 5 days of oral oseltamivir.

Oseltamivir: Oral
Eligibility criteria:
Inclusion Criteria:

Eligible patients include all patients who present to the emergency department (ED) between November and April of each influenza season, or later, at the Co-PIs' discretion, based on influenza prevalence, with the following criteria:

18 years of age or older
Laboratory confirmed positive influenza test associated with their current ED visit
Symptoms of acute respiratory illness for ≤4 days (96 hours)
Meets CDC criteria for antiviral treatment
For the purpose of this study, acute respiratory illness is defined as presence of any of the following symptoms: new or increased cough, new or increased shortness of breath, change in sputum production (for adults 65 years or older), sinus pain, nasal congestion, rhinorrhea, sore throat, subjective fever reported at time of triage or documented fever (defined here as ≥ 38 degrees Celsius).
CDC criteria for influenza antiviral treatment is defined as: being age 65 years old or older, pregnant or less than two weeks postpartum, American Indian or Alaska native, morbid obesity (BMI ≥40), a current resident of nursing home or other chronic-care facility, having chronic pulmonary disease, cardiovascular disease (except hypertension alone), renal disease, hepatic disease, hematologic disease, metabolic disorders, neurologic and neurodevelopment conditions, immunosuppression (including that caused by medications or by HIV infection), being admitted to inpatient or an observation unit, or having a clinical diagnosis of pneumonia (by the ED physician).

Exclusion Criteria:

Does not speak and understand English (or English or Spanish)
Unable or unwilling to provide informed consent
Previously enrolled in the study during the current influenza season
Unable to take oral medication
Unable to comply with all planned study procedures including availability for follow-up and willingness to complete study diary and self-assessment
Use of neuraminidase inhibitors within the past seven days
Known allergic reaction to neuraminidase inhibitors
Pregnant or breastfeeding
End-stage renal disease, defined as 9a. Currently undergoing dialysis (either hemo or peritoneal); or 9b. Creatinine clearance (CrCl) of <10 mL/min.
End-stage liver disease, as determined by the treating ED provider
Glucose-6-phosphate dehydrogenase (G6PD) deficiency by patient report
Immunodeficiency, defined as:

12a. Solid organ transplant patients receiving immunosuppression; 12b. Hematopoietic stem cell transplant patients within 12 months of transplant or with ongoing immunosuppression; 12c. Oncology patients who have had chemotherapy within the past 30 days; 12d. Current treatment with steroids equivalent to 10 mg of prednisone or more per day for greater than two weeks; 12e. Rheumatologic patients receiving immunosuppressive therapy; or 12f. HIV patients who meet one of the following criteria: 12fi. Have a cluster of differentiation 4 (CD4) cell count of <200 cells/mm3 within the past 3 months ; 12fii. Not actively receiving highly active antiretroviral therapy (HAART); or 12fiii. Have an absolute lymphocyte count <1.0 x 103 cells/μL conducted at the current ED visit