What are the differences in symptoms and treatment between Lower Respiratory Tract Infection (LRTI) and Upper Respiratory Tract Infection (URTI)?

Distinguishing LRTI from URTI: Anatomical Location and Clinical Presentation

Upper respiratory tract infections (URTIs) affect structures above and including the larynx (nose, pharynx, sinuses), presenting primarily with coryza, sore throat, and nasal symptoms, while lower respiratory tract infections (LRTIs) affect structures below the larynx (trachea, bronchi, lungs), presenting with cough, dyspnea, pathological sputum production, and potentially hypoxia or pulmonary infiltrates. 1

Anatomical Differentiation

URTI involves:

• Nose, pharynx, larynx, conjunctivae, and sinuses 1
• Samples obtained from these sites confirm URTI 1

LRTI involves:

• Trachea, bronchus, bronchoalveolar sites 1
• Samples from these lower sites confirm LRTI 1

Clinical Symptom Patterns

URTI Symptoms

• Predominantly upper respiratory symptoms: coryza (runny nose), sore throat, nasal congestion 1, 2
• Absence of dyspnea and normal respiratory rate 2
• Examples include sinusitis, rhinitis, and laryngitis 1

LRTI Symptoms

• Cough as the main symptom plus at least one of the following: 3
  • Pathological sputum production 1, 3
  • Dyspnea or shortness of breath 1, 3
  • Hypoxia 1
  • Pulmonary infiltrates on imaging 1
  • Chest discomfort or pain 3
• Examples include bronchitis, bronchiolitis, and pneumonia 1

Diagnostic Approach for Suspected Pneumonia

Suspect pneumonia when acute cough is present with any of: 1, 3, 2

• New focal chest signs on auscultation 1, 2
• Dyspnea or tachypnea 1, 2
• Fever lasting >4 days 1, 2
• Pulse rate >100 bpm 2
• Dull percussion note or pleural rub 2

Confirm with chest radiograph when pneumonia is suspected based on these clinical criteria 1, 3, 2

C-Reactive Protein (CRP) Utility

• CRP <20 mg/L: pneumonia highly unlikely 2
• CRP >100 mg/L: pneumonia likely 2
• Use CRP to refine clinical suspicion before ordering chest X-ray 2

Treatment Differences

URTI Management

• Antibiotics generally NOT indicated for uncomplicated URTI 1
• Symptomatic treatment: dextromethorphan or codeine for bothersome dry cough 1
• Avoid: expectorants, mucolytics, antihistamines, and bronchodilators in acute LRTI in primary care 1

LRTI Antibiotic Indications

Consider antibiotics in the following situations: 1, 3

• Suspected or confirmed pneumonia 1, 3
• Selected COPD exacerbations (all three symptoms: increased dyspnea, increased sputum volume, increased sputum purulence) 1
• Age >75 years with fever 1, 3
• Cardiac failure 1, 3
• Insulin-dependent diabetes mellitus 1, 3
• Serious neurological disorders 1, 3

First-Line Antibiotic Choices

For LRTI requiring antibiotics: 1, 3, 4

• First choice: Tetracycline or amoxicillin 1, 3
• Alternative (if hypersensitivity): Newer macrolides (azithromycin, roxithromycin, clarithromycin) in areas with low pneumococcal macrolide resistance 1, 3
• For resistant organisms: Levofloxacin or moxifloxacin when clinically relevant bacterial resistance exists against first-choice agents 1
• Amoxicillin-clavulanate specifically indicated for beta-lactamase-producing organisms causing LRTI 4

Etiological Considerations

Viral pathogens predominate in both URTI and LRTI: 5, 6

• Respiratory viruses identified in 50-63% of LRTI cases 5, 6
• Most common: rhinoviruses (33%), influenza viruses (24%) 6
• Bacterial etiology found in only 11-26% of LRTI cases 5
• Critical point: The frequency distribution of etiologies for URTI is similar to LRTI, except Mycoplasma pneumoniae is more common in LRTI 5

Bacterial aetiology is clinically indistinguishable from viral aetiology in LRTI, making empirical antibiotic decisions challenging 6

Common Pitfalls to Avoid

• Failing to consider alternative diagnoses: cardiac failure (in patients >65 years with orthopnea, displaced apex beat, history of MI), pulmonary embolism (history of DVT, recent immobilization, malignancy), or chronic airway disease 1, 3
• Over-prescribing antibiotics: Most LRTIs are viral and self-limiting; antibiotics are prescribed to >2/3 of patients but are only beneficial in pneumonia and selected COPD exacerbations 7
• Misdiagnosing tracheitis as asthma when wheezing is present 3
• Assuming all lower respiratory symptoms require antibiotics: Only pneumonia and specific COPD exacerbations with all three cardinal symptoms benefit from antibiotics 1, 7

Follow-Up Recommendations

• Advise patients to return if symptoms persist >3 weeks 3
• Clinical improvement expected within 3 days of antibiotic initiation; patients should contact their doctor if no improvement 3
• Seriously ill patients (high fever, tachypnea, dyspnea, relevant comorbidity, age >65 years) should be reassessed 2 days after initial visit 3