What are the differences between acute bronchitis and viral upper respiratory infection in adults?

Distinguishing Acute Bronchitis from Viral Upper Respiratory Infection in Adults

Acute bronchitis and viral upper respiratory infections (URIs) are overlapping manifestations of the same viral illness affecting different anatomical locations, with bronchitis distinguished primarily by cough as the dominant symptom plus lower respiratory tract involvement (dyspnea, chest discomfort, wheezing), while URIs present predominantly with upper airway symptoms (nasal congestion, rhinorrhea, sore throat, sneezing). 1, 2

Anatomical Location

• Upper respiratory tract infections affect structures above the larynx including the nose, sinuses, pharynx, and larynx 2
• Acute bronchitis involves inflammation of the large airways (bronchi) below the larynx 3, 2
• In clinical practice, differentiating tracheitis from acute bronchitis based on symptoms alone is often impossible 2

Clinical Presentation Differences

Acute Bronchitis Features:

• Cough is the predominant and primary complaint, lasting up to 3-6 weeks, with or without sputum production 3, 1
• At least one sign of lower respiratory tract involvement: dyspnea, chest pain/discomfort, wheezing, or diffuse/focal signs on auscultation 3, 1
• Retrosternal burning sensation may be present 3
• Inconstant fever, generally slightly raised 3
• Normal auscultation or diffuse bronchial rales 3
• Productive cough and purulent sputum are more common than in URI 4

Viral Upper Respiratory Infection Features:

• Nasal congestion and rhinorrhea are the hallmark symptoms 3, 1
• Sneezing and sore throat predominate 1
• Cough may be present in up to 83% within the first 2 days, but as a secondary symptom rather than the primary complaint 1
• Symptoms typically resolve within 2 weeks 1

Critical Diagnostic Consideration

The most important clinical task is ruling out pneumonia, not differentiating bronchitis from URI. 3, 1 For healthy immunocompetent adults younger than 70 years, pneumonia is unlikely in the absence of ALL of the following: 3, 5

• Tachycardia (heart rate >100 beats/min)
• Tachypnea (respiratory rate >24 breaths/min)
• Fever (oral temperature >38°C)
• Abnormal chest examination findings (rales, egophony, tactile fremitus, or focal consolidation)

If any of these vital sign abnormalities or focal findings are present, obtain a chest radiograph to exclude pneumonia 1, 2

The Overlap Problem

Research demonstrates considerable overlap between these conditions, with one study showing that the diagnostic model explained only 37% of the variation between acute bronchitis and URI diagnoses 6. The strongest independent predictors of acute bronchitis versus URI were:

• Cough (adjusted odds ratio 21.12) 6
• Wheezing on examination (adjusted odds ratio 12.16) 6
• Absence of nausea 6

Current evidence suggests that sinusitis, URI, and acute bronchitis may be variations of the same clinical condition (acute viral respiratory infection) affecting different anatomic areas rather than distinct disease entities. 6

Common Etiology

• More than 90% of both acute bronchitis and URIs are caused by viruses, including influenza A and B, parainfluenza, respiratory syncytial virus, coronavirus, rhinovirus, and adenovirus 3, 7
• Bacterial causes account for less than 10% of acute bronchitis cases 3, 7
• The only bacteria definitively linked to acute bronchitis in healthy adults are Mycoplasma pneumoniae, Chlamydophila pneumoniae, Bordetella pertussis, and Bordetella parapertussis, each accounting for <1% of cases 7

Management Implications

Antibiotics are not indicated for either condition in otherwise healthy adults. 3, 7

• Antibiotic treatment of acute bronchitis may decrease cough duration by only 0.5 days while exposing patients to adverse effects 1
• Supportive care and symptom management are recommended for both conditions 1, 2
• Purulent or green/yellow sputum does NOT indicate bacterial infection—it results from inflammatory cells or sloughed epithelial cells and is a common misconception leading to inappropriate antibiotic prescribing 3, 7, 8

Important Caveats

• Consider lung function testing if at least two of the following are present: wheezing, prolonged expiration, smoking history, or allergy symptoms, to identify masked asthma or COPD 1
• Approximately 40% of patients with acute bronchitis develop transient airflow obstruction and bronchial hyperresponsiveness that resolves within 6 weeks 3, 1
• Advise patients to return if symptoms persist for >3 weeks, as this may suggest asthma rather than acute bronchitis 1, 2
• Up to 45% of patients with acute cough lasting more than 2 weeks actually have asthma or COPD 1