What are the diagnostic criteria for a common cold?

Diagnosing the Common Cold

The common cold is diagnosed clinically based on characteristic symptoms—primarily nasal symptoms (rhinorrhea, congestion) with or without fever, sore throat, and cough—without requiring any laboratory testing or imaging in the vast majority of cases. 1

Clinical Diagnostic Criteria

The common cold is defined as a minor, acute respiratory illness characterized by:

• Nasal symptoms (the hallmark): nasal congestion and mucus discharge 1, 2
• Rhinorrhea (runny nose) 2
• Sneezing 2
• Throat irritation or sore throat 1, 2
• Postnasal drip and throat clearing 2
• Cough (may or may not be present initially) 1, 2
• Fever (common in children during first 3 days, less common in adults) 3
• General malaise 2
• Lacrimation (tearing) 1
• Hoarseness 1

The diagnosis is essentially a cultural concept based on self-recognition rather than a strictly defined clinical entity, as there is no single pathognomonic finding and symptoms vary considerably between individuals. 4

Key Diagnostic Principle: Rule Out Serious Conditions First

Before diagnosing a common cold, you must exclude potentially life-threatening conditions that can present with acute cough or respiratory symptoms. 1 The first step is determining whether symptoms suggest a serious illness versus a benign upper respiratory infection. 1

Red Flags Requiring Further Investigation

Immediately investigate if any of these are present:

• Hemoptysis (any amount)—requires chest radiograph and possible bronchoscopy 1, 5
• Prominent systemic illness 1
• Suspicion of inhaled foreign body—mandatory specialist referral for bronchoscopy 1, 5
• Suspicion of lung cancer 1
• Acute breathlessness—assess for asthma or anaphylaxis 1
• Fever with malaise and purulent sputum—assess for pneumonia 1
• Change in voice—may indicate vocal cord palsy 1

Physical Examination Findings

Early common cold examination findings: 1

• Inflamed nasal mucosa with adherent or draining secretions
• Inflamed posterior pharynx with secretions
• Possible serous otitis on ear examination

Lower respiratory tract examination is typically normal in uncomplicated common cold. 1

Findings suggesting pneumonia (not common cold): 1

• Dullness on percussion
• Bronchial breathing
• Crackles on auscultation

Critical Diagnostic Pitfall: Do Not Diagnose Bacterial Sinusitis Early

Bacterial sinusitis cannot be accurately diagnosed during the first week of symptoms, even with imaging abnormalities. 1

• 87% of patients with viral colds show sinus abnormalities on CT scan 1
• 79% of these abnormalities resolve without antibiotics by days 13-20 1
• The term "viral rhinosinusitis" is more accurate than separating rhinitis from sinusitis during acute viral infection 1
• Clinical judgment is required, but bacterial sinusitis diagnosis should not be made in the first week 1

When to Consider Alternative Diagnoses

Rule Out Acute Bronchitis

Do not diagnose acute bronchitis unless common cold has been ruled out, as acute bronchitis is often overdiagnosed, leading to inappropriate antibiotic prescriptions. 1 The definitions are similar, but common cold should be diagnosed when acute nasal symptoms predominate. 1

Rule Out Asthma

30-65% of patients with asthma presenting as acute cough have been misdiagnosed as having acute bronchitis. 1 Consider asthma if there is acute cough with increasing breathlessness. 1

No Laboratory Testing or Imaging Required

Routine diagnostic testing is not indicated for common cold diagnosis. 1

• Viral testing is not feasible due to the numerous viruses that cause colds and variability in disease presentation 4
• Sinus imaging has no clinical specificity for bacterial infection within the first week 1
• Chest radiograph is only indicated if red flags are present 1

Natural History to Support Clinical Diagnosis

Understanding the typical course helps confirm the diagnosis:

• Symptom onset: Sore throat is often the harbinger, accompanied by nasal congestion, runny nose, and headache 6
• Duration in adults: Less than 7 days typically 3
• Duration in children: 10-14 days 3
• Peak symptoms: Days 1-4 with substantial overlap of nasal congestion, secretory symptoms, and pain 6
• Persistent symptoms: 25% of patients continue to have cough and nasal discharge at day 14—this is normal and does not indicate bacterial infection 1, 5

Practical Diagnostic Approach

1. Identify characteristic nasal symptoms as the predominant feature 1
2. Exclude red flags requiring immediate investigation 1, 5
3. Perform focused physical examination looking for inflamed nasal mucosa and pharynx 1
4. Ensure lower respiratory examination is normal (no pneumonia signs) 1
5. Do not order imaging or laboratory tests unless red flags present 1
6. Reassure that symptoms lasting up to 14 days are normal 5, 3