Swine Flu (H1N1) Symptoms, Complications & When to Seek Care

Swine flu (influenza A H1N1pdm09) causes typical influenza illness; some strains had higher pediatric severity.

Common Symptoms (Onset 1–4 days post-exposure)

• Fever/chills (often high, but not universal)
• Cough (usually dry)
• Sore throat
• Rhinorrhea/nasal congestion
• Myalgia, headache, fatigue
• GI: nausea, vomiting, diarrhea (more common than seasonal flu)

High-Risk Groups for Complications

• Children <5y (especially <2y), adults ≥65y
• Pregnant/postpartum (≤2 weeks)
• Chronic: asthma, COPD, CVD, diabetes, CKD, liver disease, immunosuppression
• BMI ≥40
• Residents of nursing homes

Serious Complications

• Primary viral / secondary bacterial pneumonia
• ARDS, respiratory failure
• Myocarditis, pericarditis
• Encephalitis, febrile seizures
• Multi-organ failure, sepsis
• Death

When to Seek Medical Care

• Emergency: Difficulty breathing, chest pain, cyanosis, confusion, persistent vomiting, dehydration, seizures, worsening after initial improvement.
• High-risk individuals: Contact provider early (within 48h) for antiviral consideration.

Treatment

• Antivirals (oseltamivir, zanamivir, peramivir, baloxavir): Best if started ≤48h; still beneficial later in severe/high-risk.
• Supportive: fluids, rest, antipyretics (avoid aspirin in <18y).

Prevention

• Annual influenza vaccine (includes H1N1pdm09).
• Hand hygiene, respiratory etiquette, masking when ill.