Influenza resident survival guide
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Mohammad Braizat, M.S. [2]
Resident Survival Guide
Resident Survival Guide
This point-of-care quick-reference covers the rapid recognition, testing, and antiviral management of seasonal influenza in outpatients and hospitalized patients. For detailed clinical presentation, see History and Symptoms and Physical Examination. For vaccine information, see Primary Prevention. For diagnostic test characteristics, see Laboratory Findings.
Core Principle
The single highest-yield principle, reinforced by every current guideline, is: start antiviral treatment as early as possible—ideally within 48 hours of onset—for any patient who is hospitalized, has severe/progressive illness, or is at high risk for complications, without waiting for test results.[1][2][3]
Overview
Influenza is an acute respiratory illness caused by influenza A and B viruses (Orthomyxoviridae). Hallmarks are abrupt fever, cough, myalgias, headache, sore throat, and malaise. Because signs overlap with SARS-CoV-2, RSV, and other pathogens, clinical diagnosis alone is unreliable, and multiplex testing is often warranted when these viruses cocirculate.[1][4]
Step 1 — Identify High-Risk Patients (Drives Testing and Treatment)
Antiviral treatment is prioritized for patients at increased risk of complications. High-risk groups per CDC/IDSA/AAP:[2][3]
- Children <2 years
- Adults ≥65 years
- Chronic pulmonary, cardiovascular, renal, hepatic, neurologic, hematologic, or metabolic disorders (including diabetes mellitus)
- Immunosuppression (including HIV, malignancy, transplant, chronic steroid use)
- Pregnancy and postpartum (within 2 weeks)
- Morbid obesity (BMI ≥40)
- Residents of long-term care facilities
- Native American and Alaska Native persons
Step 2 — Who to Test
Testing should not delay empiric antiviral treatment in high-risk or hospitalized patients.[3][2]
- Hospitalized patients with acute respiratory illness (with or without fever), exacerbation of chronic cardiopulmonary disease, or new in-hospital respiratory symptoms: test with a molecular assay.
- High-risk outpatients with influenza-like illness: test if it will influence antiviral or chemoprophylaxis decisions—but do not delay empiric treatment for the result.
- Low-risk outpatients likely discharged home: test selectively if it will reduce unnecessary antibiotics/further testing or guide prophylaxis for high-risk contacts.
- In-hospital H5 surveillance: per CDC (2025), expedite subtyping of influenza A specimens from hospitalized/ICU patients given ongoing avian A(H5) activity.[3]
Step 3 — Choose the Right Test
Rapid molecular assays (NAAT) are now preferred; rapid antigen tests (RIDTs) have poor sensitivity and negatives must be confirmed.[5][3]
| Method | Sensitivity / Specificity | Time to Result | Practical Role | References |
|---|---|---|---|---|
| Rapid molecular assay (POC NAAT) | High / High | 15–30 min | Preferred point-of-care test; outperforms antigen testing in ED | [5][1] |
| RT-PCR / lab NAAT (incl. multiplex flu/SARS-CoV-2/RSV) | High / High (gold standard) | ~1–8 h | Preferred for hospitalized patients; distinguishes coinfection | [5][1] |
| Rapid antigen test (RIDT) | Low–moderate (50–75%) / High | 10–30 min | Confirm negatives with NAAT during high activity; false positives in low-prevalence periods | [5][1] |
| Immunofluorescence (DFA/IFA) | Moderate / High | 1–4 h | Rarely used | [5][1] |
| Viral culture | High / High | 1–10 days | Not for clinical decisions; needed for strain characterization | [5][1] |
| Serology | — | Days | Not recommended for acute diagnosis | [5][1] |
Specimen collection: Nasopharyngeal specimens have the highest yield; mid-turbinate or combined nasal/throat swabs are acceptable depending on the assay. In hospitalized patients with respiratory failure and negative upper-tract specimens, test lower-respiratory specimens. Do not test blood, serum, CSF, urine, or stool.[1][5]
Step 4 — Treat
Start treatment as soon as possible; benefit is greatest within 24–48 hours but still worthwhile beyond 48 hours in hospitalized, severe, or high-risk patients.[1][2]
Who to Treat
- Always/ASAP: any hospitalized patient with suspected or confirmed influenza; severe, complicated, or progressive illness; any high-risk outpatient (including pregnancy)—empirically, without waiting for testing.[2][3][1]
- Consider: otherwise healthy outpatients presenting ≤48 hours from onset, and symptomatic contacts/healthcare workers of severely immunocompromised persons.
Drug Selection
- Oseltamivir is the preferred agent for hospitalized, severe/complicated, or high-risk patients, and the only agent with abundant pregnancy safety data.[2][1]
- Baloxavir, peramivir, or zanamivir are alternatives for uncomplicated influenza in eligible outpatients.[6]
- Amantadine/rimantadine are NOT recommended due to near-universal resistance.[2]
| Agent | Treatment Dose | Post-Exposure Prophylaxis Dose | Key Limits | References |
|---|---|---|---|---|
| Oseltamivir (oral) | Adults: 75 mg BID ×5 d Children ≥1 y (weight-based): ≤15 kg → 30 mg BID; >15–23 kg → 45 mg BID; >23–40 kg → 60 mg BID; >40 kg → 75 mg BID Children <1 y: 3 mg/kg BID |
75 mg once daily ×7 d after exposure (adults); weight-based in children | Renal adjustment: CrCl >30–60 → 30 mg BID CrCl >10–30 → 30 mg once daily HD/ESRD → 30 mg after each HD session Preferred in pregnancy and hospitalized Off-label but CDC/AAP recommended for hospitalized children and neonates from birth (FDA label ≥2 weeks) |
[1][3][7] |
| Baloxavir (oral, single dose) | ≥5 y (otherwise healthy): <20 kg → 2 mg/kg (suspension) 20 to <80 kg → 40 mg ≥80 kg → 80 mg High-risk patients: FDA-approved from age ≥12 y |
Same single dose within 48 h of exposure | NOT for hospitalized, severe/progressive, severely immunocompromised, or pregnancy/breastfeeding per CDC | [1][6][3][8][9] |
| Peramivir (IV, single dose) | Adults: 600 mg IV once Children 6 mo–12 y: 12 mg/kg (up to 600 mg) IV once |
Not approved | Useful if oral not tolerated Note: FDA-approved ≥6 mo; CDC materials may still reference older ≥2 y cutoff |
[2][8][10] |
| Zanamivir (inhaled) | ≥7 y: 10 mg BID ×5 d | ≥5 y: 10 mg once daily ×7 d | Avoid in asthma/COPD (bronchospasm) | [2][1] |
Comparative Points
- Single-dose baloxavir has greater antiviral efficacy, superior efficacy against influenza B, better GI tolerability, and may reduce onward transmission versus oseltamivir—but carries higher treatment-emergent resistance (notably A/H3N2 and young children) and cost.[1][6][3]
- The 2025 network meta-analysis found baloxavir probably reduces symptom duration (~−1 day) and hospitalization in high-risk patients with fewer adverse events than oseltamivir; all agents had little or no effect on mortality.[11]
Step 5 — Post-Exposure Chemoprophylaxis
Reserve for high-risk contacts who are unvaccinated or inadequately protected; it is an adjunct to—not a substitute for—vaccination.[3][12]
Zanamivir, oseltamivir, laninamivir, and baloxavir all probably reduce symptomatic seasonal influenza in high-risk exposed persons (moderate certainty) but have little effect in low-risk persons.[12]
Start within 48 hours of exposure; do not use once-daily prophylactic dosing to treat symptomatic disease.[3]
The following algorithm operationalizes the chemoprophylaxis decision by risk and vaccination status:
Template:Family tree/summary= Influenza Post-Exposure Chemoprophylaxis Algorithm| High-risk contact exposed to influenza within 48 hours | |||||||||||||||||||||
| Was the contact vaccinated? | |||||||||||||||||||||
| Yes | No | ||||||||||||||||||||
| Is the vaccine well-matched to circulating strains? | Offer chemoprophylaxis (oseltamivir, baloxavir, or zanamivir) | ||||||||||||||||||||
| Yes → No prophylaxis needed | |||||||||||||||||||||
Guideline Context
The 2024 WHO influenza guideline (summarized in BMJ, 2026) conditionally recommends, within 48 hours of onset:[13]
- Oseltamivir for severe influenza
- Baloxavir for patients at high risk of progression from non-severe illness
WHO recommends against antibiotics in non-severe influenza (strong recommendation) and against corticosteroids, macrolides, mTOR inhibitors, NSAIDs, and passive immunotherapy in severe influenza (conditional recommendations).[13]
Symptomatic Therapy
Antipyretics/analgesics (acetaminophen, NSAIDs) for fever and myalgias; decongestants for congestion; antitussives for cough. These relieve symptoms but do not affect the virus and do not replace antivirals in indicated patients.
Avoid aspirin in children and adolescents with influenza due to Reye syndrome risk.[3]
Information Removed from the Legacy Version and Why
- Amantadine/rimantadine as usable agents — removed as treatment/prophylaxis options; obsolete due to near-universal resistance.[2]
- Zanamivir/oseltamivir framed as “the two main antivirals” — updated; four agents are now FDA-approved, and baloxavir is a distinct mechanistic class.[2][6]
- Rapid antigen testing implied as adequate first-line — corrected; rapid molecular assays are now preferred, with negative RIDTs requiring NAAT confirmation.[5][3]
- Reliance on the 2018 IDSA guideline alone — supplemented with CDC (2025), AAP (2025–2026), IDSA/ASM microbiology (2024), and WHO (2024) guidance.
- Non-clinical/dated references (newspaper citations, American Lung Association web link) — replaced with primary guideline sources.
Important Updates Compared with Older Teaching
- Baloxavir (single oral dose) is now approved for treatment (otherwise healthy ≥5 y; high-risk ≥12 y) and post-exposure prophylaxis (≥5 y).[8][9]
- Molecular assays are preferred; RIDTs are second-line.[5]
- Multiplex flu/SARS-CoV-2/RSV testing is standard when viruses cocirculate.[1][3]
- Expedited influenza A subtyping in hospitalized patients given avian A(H5) activity.[3]
- Peramivir is FDA-approved down to 6 months of age (though CDC materials may still reference ≥2 years).[8][10]
- Oseltamivir is recommended off-label by CDC/AAP for hospitalized children and neonates from birth, diverging from FDA labeling (≥2 weeks).[3]
Areas of Uncertainty and Controversy
- Baloxavir positioning: FDA approves it for otherwise-healthy patients ≥5 y and high-risk patients ≥12 y, but CDC restricts it (not for hospitalized, severe/progressive, severely immunocompromised, or pregnant/breastfeeding patients).[3][2]
- Treatment-emergent baloxavir resistance (PA/I38X), higher in children and A/H3N2, with documented household transmission.[1]
- Combination antiviral therapy in immunocompromised hosts is biologically plausible but unproven by RCT.[1]
- Evidence certainty for antivirals in severe/hospitalized influenza remains low, resting largely on observational data.[11][13]
High-Yield Clinical Pearls
- Do not wait for test results to treat hospitalized or high-risk patients—treat empirically.[2][4]
- Oseltamivir is the preferred agent in pregnancy (abundant safety data); baloxavir is not recommended.[1][3]
- Baloxavir’s single dose helps when adherence or GI tolerance is a concern, and it is superior for influenza B.[3][6]
- A negative rapid antigen test does not rule out influenza during high activity—confirm with NAAT.[5]
- Avoid inhaled zanamivir in asthma/COPD (bronchospasm risk).[2]
- Oseltamivir is recommended off-label by CDC/AAP for hospitalized children and neonates from birth.[3]
Common Pitfalls
- Using or citing amantadine/rimantadine — obsolete.[2]
- Relying on rapid antigen tests and acting on false negatives.[5][1]
- Delaying antivirals pending confirmation in high-risk/hospitalized patients.[3]
- Prescribing baloxavir in pregnancy, hospitalized, or severely immunocompromised patients — outside CDC guidance.[3]
- Using once-daily prophylactic dosing to treat symptomatic influenza.[3]
- Giving aspirin to children/adolescents with influenza (Reye syndrome).[3]
- Prescribing baloxavir for high-risk patients aged 5–11 years — FDA approval for high-risk use starts at ≥12 years.[2][3]
References
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 Uyeki TM, Hui DS, Zambon M, Wentworth DE, Monto AS (2022). “Influenza”. Lancet (London, England). 400 (10353): 693–706. doi:10.1016/S0140-6736(22)00982-5.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 Influenza. Molly Valleau and Christine M. Szablewski. CDC Yellow Book. 2025.
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 3.22 3.23 3.24 Committee on Infectious Diseases (2025). “Recommendations for Prevention and Control of Influenza in Children, 2025-2026: Technical Report”. Pediatrics. 156 (6): e2025073622. doi:10.1542/peds.2025-073622.
- ↑ 4.0 4.1 Uyeki TM, Santoli J, Jernigan DB (2020). “Preparing for the 2020-2021 Influenza Season”. JAMA. 324 (22): 2318–2319. doi:10.1001/jama.2020.21849.
- ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 Miller JM, Binnicker MJ, Campbell S; et al. (2024). “Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases: 2024 Update by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM)”. Clinical Infectious Diseases: ciae104. doi:10.1093/cid/ciae104.
- ↑ 6.0 6.1 6.2 6.3 6.4 Zambon M, Hayden FG (2025). “Influenza A(H3N2) Subclade K Virus”. JAMA. doi:10.1001/jama.2025.25903.
- ↑ Oseltamivir/Tamiflu FDA label.
- ↑ 8.0 8.1 8.2 8.3 FDA Orange Book. FDA Orange Book.
- ↑ 9.0 9.1 Xofluza. Food and Drug Administration. Updated date: 2025-12-15.
- ↑ 10.0 10.1 Rapivab FDA Orange Book, 2024.
- ↑ 11.0 11.1 Gao Y, Zhao Y, Liu M; et al. (2025). “Antiviral Medications for Treatment of Nonsevere Influenza”. JAMA Internal Medicine. 185 (3): 293–301. doi:10.1001/jamainternmed.2024.7193.
- ↑ 12.0 12.1 Zhao Y, Gao Y, Guyatt G; et al. (2024). “Antivirals for Post-Exposure Prophylaxis of Influenza: A Systematic Review and Network Meta-Analysis”. Lancet (London, England). 404 (10454): 764–772. doi:10.1016/S0140-6736(24)01357-6.
- ↑ 13.0 13.1 13.2 Vandvik PO, Agarwal A, Rylance J; et al. (2026). “Summary of WHO Clinical Practice Guidelines for Influenza”. BMJ (Clinical Research Ed.). 392: e087397. doi:10.1136/bmj-2025-087397.
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