What are the differences between flu and cold symptoms and how are they treated?

Distinguishing Flu from Cold: Key Clinical Differences

Influenza is characterized by abrupt onset of high fever, severe myalgia, and prostrating malaise that confines patients to bed, while the common cold presents with gradual onset of predominantly nasal symptoms, mild or absent fever, and minimal systemic symptoms. 1, 2

Primary Symptom Differences

Influenza Presentation

• Abrupt onset within hours of constitutional and respiratory symptoms 1, 2
• High fever (typically >38.5°C) is the hallmark distinguishing feature 1, 3
• Severe myalgia and headache that are incapacitating 1, 2
• Profound malaise requiring bed rest 1
• Nonproductive cough that is prominent and persistent 1, 2
• Sore throat and rhinitis present but secondary to systemic symptoms 1
• Symptoms peak rapidly within 24-48 hours 2

Common Cold Presentation

• Gradual onset over 1-2 days 4
• Minimal or absent fever (if present, typically low-grade) 5, 4
• Mild myalgia or none at all 4
• Nasal symptoms predominate: rhinorrhea, sneezing, nasal congestion 4
• Sore throat often the initial symptom 4
• Patients remain functional and rarely bedridden 5
• Cough mild and develops later in course 4

Clinical Predictors of Influenza

The combination of cough AND fever has a 79% positive predictive value for influenza when the virus is circulating in the community. 3 This rises with increasing temperature at presentation 3.

High-Value Discriminating Features

• Fever ≥38.5°C with cough: 64% of influenza patients vs. 33% without influenza 3
• Nasal congestion with fever and cough: 91% sensitivity for influenza 3
• Inability to perform daily activities: specific for influenza 1, 5
• Symptom onset within 12-24 hours: characteristic of influenza 2

Disease Course Differences

Influenza Timeline

• Incubation period: 1-4 days (average 2 days) 2
• Infectious period: day before symptoms through 5-6 days after onset in adults 2
• Uncomplicated illness resolves in 3-7 days 2
• Cough and malaise persist >2 weeks even after resolution 2

Common Cold Timeline

• Gradual symptom development over 1-2 days 4
• Peak symptoms at 2-3 days 4
• Resolution typically within 7-10 days 4
• Minimal post-illness fatigue 4

Age-Specific Presentations

Children with Influenza

• May present with high fever mimicking bacterial sepsis 1, 2
• Febrile seizures occur in 6-20% of hospitalized children 1
• Otitis media, nausea, and vomiting are common (25% develop otitis media) 1, 6
• Infants may show only irritability, poor feeding, and lethargy 6

Children with Colds

• Predominantly nasal symptoms without high fever 4
• Maintain normal activity levels 5
• Minimal systemic symptoms 4

Treatment Approach Differences

Influenza Management

• Symptomatic treatment: paracetamol or ibuprofen for fever, myalgia, and headache 1
• Rest and abundant fluid intake 1
• Avoid smoking 1
• Consider short-course topical decongestants, throat lozenges, saline nasal drops 1
• Antiviral therapy (oseltamivir) if within 48 hours of symptom onset and high-risk features 1
• Aspirin contraindicated in children <16 years due to Reye syndrome risk 1, 6

Common Cold Management

• Symptomatic relief with over-the-counter remedies 1
• Decongestants and antihistamines 4
• No role for antiviral therapy 4
• Self-limiting, managed at home 1

Red Flags Requiring Re-evaluation

Warning Signs in Influenza

• Shortness of breath at rest or with minimal activity 1
• Painful or difficult breathing 1
• Bloody sputum 1
• Fever persisting 4-5 days without improvement 1, 6
• Drowsiness, disorientation, or confusion 1
• Initial improvement followed by recurrent high fever (suggests bacterial superinfection) 6
• Failure to improve within 48 hours of starting antivirals 1

Common Cold Complications (Rare)

• Symptoms persisting >10 days may indicate bacterial sinusitis 4
• Development of high fever suggests secondary infection 4

Critical Clinical Pitfalls

Respiratory illnesses caused by influenza are difficult to distinguish from other respiratory pathogens based on symptoms alone, with clinical definitions showing only 63-78% sensitivity and 55-71% specificity compared to viral culture. 2 However, when influenza is known to be circulating in the community, the presence of cough plus fever within 48 hours of symptom onset provides sufficient clinical certainty to initiate antiviral therapy in high-risk patients 3.

The key distinguishing feature remains fever intensity and rapidity of onset: influenza causes abrupt high fever with prostration, while colds cause gradual onset with minimal fever and preserved function 1, 2, 5.