How should rigors associated with influenza be managed, including antiviral therapy, antipyretics, supportive care, and criteria for urgent medical attention, particularly in high‑risk patients?

Management of Rigors Associated with Influenza

For rigors (severe chills) with influenza, use acetaminophen or ibuprofen as first-line antipyretic therapy to alleviate distressing symptoms, initiate oseltamivir 75 mg twice daily for 5 days if the patient presents within 48 hours of symptom onset (or beyond 48 hours if high-risk features are present), and ensure close monitoring for warning signs requiring urgent medical attention. 1

Symptomatic Management of Rigors and Fever

Antipyretic Therapy:

• Acetaminophen (paracetamol) is the preferred first-line agent for managing fever and rigors based on its favorable safety profile 1
• Ibuprofen serves as an alternative antipyretic option 1
• The goal is to alleviate distressing symptoms (rigors, fever, myalgias), not merely to reduce body temperature 1
• Continue treatment only while symptoms of fever and discomfort persist 1
• Never use aspirin in children under 16 years due to Reye's syndrome risk 2, 1

Supportive Care Measures:

• Ensure adequate hydration (drinking plenty of fluids, but no more than 2 liters per day) 1
• Encourage rest and avoiding smoking 1
• Consider short-term topical decongestants, throat lozenges, or saline nose drops as needed 2, 1

Antiviral Therapy Decision Algorithm

Within 48 Hours of Symptom Onset:

• Oseltamivir 75 mg every 12 hours for 5 days should be initiated for patients presenting with acute influenza-like illness, fever (>38°C), and symptoms for two days or less 3, 1
• Dose reduction to 75 mg once daily is required if creatinine clearance is <30 mL/min 3, 4

Beyond 48 Hours of Symptom Onset:

• Do not give oseltamivir to otherwise healthy outpatients presenting more than 48 hours after symptom onset, as no data support symptomatic benefit 2
• However, oseltamivir should still be given if any high-risk features are present, as mortality benefit persists when initiated up to 96 hours after symptom onset in high-risk patients 2

High-Risk Features Requiring Antiviral Therapy (Even Beyond 48 Hours):

• Age <2 years or ≥65 years 2, 1
• Pregnancy or postpartum status 2, 1
• Immunocompromised status 2, 1
• Chronic cardiac, pulmonary, renal, hepatic, neurologic, or metabolic disease 2, 1
• Severe or progressive illness requiring hospitalization 2
• Evidence of complications 2
• Patients unable to mount adequate febrile response (immunocompromised or very elderly) may be eligible despite lack of documented fever 3, 4

Criteria for Urgent Medical Attention

Instruct patients to return immediately if they develop:

• Shortness of breath at rest or with minimal activity 2, 1
• Painful or difficult breathing 2, 1
• Bloody sputum (hemoptysis) 2, 1
• Drowsiness, disorientation, or confusion 2, 1
• Fever persisting more than 4-5 days without improvement 2, 1
• Initial improvement followed by recurrence of high fever (suggesting bacterial superinfection) 2, 1

Hospitalization Criteria: Patients with two or more of the following unstable clinical factors should remain hospitalized 3:

• Temperature >37.8°C 3
• Heart rate >100/min 3
• Respiratory rate >24/min 3
• Systolic blood pressure <90 mmHg 3
• Oxygen saturation <90% 3
• Inability to maintain oral intake 3
• Abnormal mental status 3

Management of Severe Influenza in High-Risk Patients

Definition of Severe Influenza: Influenza meeting any of the following conditions 3:

• Persistent high fever for more than 3 days with severe cough, blood sputum, or chest pain 3
• Rapid respiratory rate, dyspnea, or cyanosis of the lips 3
• Mental abnormality (slow response, lethargy, restlessness) 3
• Dehydration due to severe vomiting and diarrhea 3
• Pneumonia 3
• Obvious aggravation of underlying diseases 3
• Other clinical conditions requiring hospitalization 3

Treatment Approach:

• Initiate oseltamivir combined with supportive therapy 3
• Monitor temperature, respiratory rate, pulse, blood pressure, mental status, oxygen saturation, and inspired oxygen concentration at least twice daily (more frequently in severe illness) 3
• Assess for cardiac complications and volume depletion; provide intravenous fluids as needed 3
• Provide nutritional support in severe or prolonged illness 3

Antibiotic Considerations

Do Not Routinely Use Antibiotics:

• Previously well adults with acute bronchitis complicating influenza do not routinely require antibiotics in the absence of pneumonia 3
• Do not reflexively prescribe antibiotics for viral influenza symptoms alone, as this contributes to antibiotic resistance 2

Consider Antibiotics If:

• Previously well adults develop worsening symptoms (recrudescent fever or increasing dyspnea) 3
• High-risk patients develop lower respiratory features 3
• Evidence of bacterial superinfection: new consolidation on chest imaging, purulent sputum production, clinical deterioration despite supportive care, elevated inflammatory markers 2

Antibiotic Selection (If Indicated):

• Preferred oral choices: co-amoxiclav or tetracycline 3
• Alternative: macrolide (clarithromycin or erythromycin) or fluoroquinolone active against S. pneumoniae and S. aureus 3

Critical Pitfalls to Avoid

• Do not withhold oseltamivir in high-risk patients based solely on timing, as mortality benefit persists even when started 48-96 hours after symptom onset 2
• Do not use aspirin in children <16 years due to Reye's syndrome risk 2, 1
• Do not use antipyretics with the sole aim of reducing body temperature; use them to alleviate distressing symptoms 1
• Do not empirically add antibiotics unless there is evidence of bacterial superinfection 2

Infection Control and Prevention

• Advise patients on transmission prevention: hand hygiene and respiratory etiquette 2
• Consider post-exposure prophylaxis with oseltamivir 75 mg once daily for 10 days for high-risk household contacts 2
• Patients should isolate at home until at least 24-48 hours after fever disappears without antipyretics 4