What is the difference in symptoms and treatment between the common cold and influenza?

Distinguishing Common Cold from Influenza: Symptoms and Treatment

Key Symptom Differences

The most reliable way to distinguish influenza from the common cold is the presence of high fever (typically 38-41°C) with abrupt onset, accompanied by severe systemic symptoms including myalgia, headache, and malaise—features that are minimal or absent in the common cold. 1

Influenza Presentation

• Fever is paramount: typically 38-40°C (can reach 41°C), peaks within 24 hours of onset, lasts 3 days (range 1-5 days) 1
• Abrupt onset of symptoms within 2-4 days incubation period 1
• Severe systemic symptoms: myalgia (affecting back and limbs), headache, malaise, fatigue, chills/sweats 1
• Respiratory symptoms: dry cough (productive in 40% of cases), sore throat, nasal congestion 1
• Clinical appearance: toxic appearance initially, flushed face, injected eyes, hot and moist skin 1
• Gastrointestinal symptoms uncommon in adults (<10%): vomiting and diarrhea rare 1
• Duration: illness typically resolves in 7 days, though cough and malaise may persist for weeks 1

Common Cold Presentation

• Low-grade or absent fever (when present, typically ≤38.5°C) 1
• Gradual onset with predominantly upper respiratory symptoms 1, 2
• Minimal systemic symptoms: mild headache, minimal myalgia 1, 3
• Prominent nasal symptoms: rhinorrhea (clear and watery), nasal congestion, sneezing, postnasal drip 1, 2
• Other symptoms: sore throat, throat clearing, mild cough 1, 2
• Duration: symptoms last up to 2 weeks 1

Critical Distinguishing Features

Fever is the single most discriminating symptom: present in 74% of COVID-19 cases, 68% of influenza cases, but only 40% of common cold cases 4. When fever exceeds 38.5°C with cough, influenza should be strongly suspected over common cold 1.

Systemic symptoms predominate in influenza: headache (91% in influenza vs 21% in COVID-19), muscular pain (94% vs 29%), and severe malaise distinguish influenza from common cold where these symptoms are minimal 4.

Nasal symptoms predominate in common cold: rhinorrhea occurs in 81-91% of common cold cases but only 4% of COVID-19 and 12% of SARS cases 4.

Treatment Approaches

Influenza Treatment

Antiviral therapy with oseltamivir 75 mg PO twice daily for 5 days should be initiated within 48 hours of symptom onset, reducing illness duration by approximately 24 hours and decreasing hospitalization rates. 5, 6

Antiviral Indications

• Start within 48 hours of symptom onset for maximum benefit 5, 6
• Dose adjustment required: 75 mg once daily if creatinine clearance <30 mL/min 5
• Alternative agent: zanamivir 10 mg inhaled twice daily for 5 days 7
• High-risk patients (chronic respiratory/cardiac disease, diabetes, immunosuppression, age ≥65 years) should receive antivirals even if presenting slightly beyond 48 hours 1

Symptomatic Management for Influenza

• Antipyretics: paracetamol or ibuprofen for fever, myalgia, and headache 1
• Rest and hydration: drinking plenty of fluids 1
• Avoid smoking 1
• Topical decongestants (short course), throat lozenges, saline nose drops as needed 1

Monitoring and Red Flags

Patients should re-consult if they fail to improve within 48 hours of starting antivirals, or develop worsening symptoms including shortness of breath, chest pain, respiratory rate >24/min, oxygen saturation <90%, or inability to maintain oral intake. 1, 5

Common Cold Treatment

Antibiotics should NOT be prescribed for common cold as the infection is viral; symptomatic therapy is the appropriate management strategy. 1, 8

Symptomatic Management for Common Cold

• Combination therapy: antihistamine-analgesic-decongestant products provide significant symptom relief in 1 out of 4 patients 1
• Antipyretics/analgesics: paracetamol or ibuprofen for fever and discomfort 1
• Nasal symptoms: inhaled ipratropium bromide, inhaled cromolyn sodium, saline nasal irrigation 1
• Cough: antitussives (codeine or dextromethorphan) for short-term relief 8
• First-generation antihistamine plus decongestant (e.g., brompheniramine/pseudoephedrine) decreases cough severity 8
• Zinc supplements: may reduce duration if started within 24 hours of symptom onset, but weigh against adverse effects (nausea, bad taste) 1

What Does NOT Work

• Antibiotics: not effective and increase adverse effects 1, 8
• Vitamin C and echinacea: no evidence of benefit 1

Critical Pitfalls to Avoid

Diagnostic Pitfalls

• Do not assume productive sputum or low-grade fever indicates bacterial infection requiring antibiotics—these are typical viral features 8
• Consider underlying asthma if patient has had two or more similar episodes in past 5 years; approximately one-third of patients with acute cough are misdiagnosed with acute bronchitis when they actually have acute asthma 8
• During influenza season, increased consultation rates for all respiratory infections (including febrile colds) can overwhelm services; triage based on illness severity and high-risk status 1

Treatment Pitfalls

• Aspirin is contraindicated in children aged under 16 years due to Reye's syndrome risk 1
• Do not prescribe antibiotics reflexively for acute bronchitis complicating influenza in previously well adults without evidence of bacterial pneumonia 5
• Children under 1 year and high-risk children with fever >38.5°C and cough should be seen by GP or A&E, not managed remotely 1

Follow-up Thresholds

• Common cold symptoms lasting >2 weeks: reassess for complications or alternative diagnosis 1
• Cough persisting 3-8 weeks: consider post-infectious cough, treat with inhaled ipratropium bromide 8
• Cough persisting >8 weeks: reclassify as chronic cough and initiate systematic evaluation for upper airway cough syndrome, asthma, then GERD 8