Influenza & Respiratory Viruses

Your patient started coughing and aching 36 hours ago — you have a 12-hour window to start the one drug that actually shortens this illness.

Influenza A and B cause seasonal respiratory illness with sudden onset of high fever (often 38.5–40°C), myalgia, headache, nonproductive cough, and profound fatigue. This differs from the common cold, which has gradual onset with rhinorrhea, sneezing, and mild malaise. Diagnosis: rapid influenza diagnostic test (RIDT) provides results in 15 minutes but has moderate sensitivity (50–70%); RT-PCR is the gold standard with higher sensitivity. A negative rapid test does not rule out influenza during peak season. Treatment: oseltamivir (Tamiflu) 75 mg twice daily for 5 days, most effective when started within 48 hours of symptom onset. After 48 hours, still recommended for hospitalized patients and those at high risk for complications. High-risk groups: adults ≥65, children <5 (especially <2), pregnant women, immunocompromised, residents of long-term care facilities, and those with chronic diseases (asthma, COPD, heart disease, diabetes). Annual vaccination is recommended for everyone ≥6 months. Inactivated influenza vaccine (injection) is appropriate for all, including pregnant women and immunocompromised. Live attenuated (nasal spray, LAIV) is an option for healthy non-pregnant individuals aged 2–49. Precautions: droplet precautions (surgical mask within 6 feet of patient). Complications: secondary bacterial pneumonia (most common cause of influenza-related death), myocarditis, encephalitis, Reye syndrome (with aspirin use in children). Nursing: monitor for secondary pneumonia (new fever spike after initial improvement, productive cough, consolidation), teach cough hygiene, isolate until afebrile for 24 hours without antipyretics, push fluids.

Key Distinctions

Influenza is sudden onset with systemic symptoms (fever, myalgia); the common cold is gradual with predominantly nasal symptoms. The 48-hour window for oseltamivir is the most tested point — but hospitalized and high-risk patients still benefit after 48 hours. Do not confuse inactivated vaccine (safe for all including pregnant and immunocompromised) with live attenuated nasal spray (contraindicated in pregnancy, immunocompromised, and children <2). Aspirin is contraindicated in children with influenza due to Reye syndrome risk — use acetaminophen or ibuprofen.

Clinical Pearl

Tamiflu has a 48-hour window — after that, it still helps the sickest patients. Clock starts at symptom onset, not diagnosis.