Respiratory Tract Infections: Causes, Symptoms, and Diagnosis

Respiratory Viral Infections: An Overview

Respiratory viral infections are the most common site of infection. Generally, these are mild, yet they carry significant economic impact. Acute respiratory infections (ARI) can occur at any level of the respiratory tract. Pneumonia is the most severe form, as it is potentially lethal and responsible for a large number of deaths.

Why the Respiratory System is Frequently Infected

• It is in direct contact with the environment.
• The environment provides a warm, moist place ideal for microbial growth.

Clinical Respiratory Tract Infections

• Viruses: Major cause of upper respiratory infections and most cases of pharyngitis.
• Bacteria: Primary cause of otitis media, sinusitis, pharyngitis, epiglottitis, bronchitis, and pneumonia.
• Fungi and Protozoa: Rarely cause severe infections in healthy individuals, but are significant in immunocompromised patients.

Pathogens by Respiratory Level

Specific Respiratory Conditions

Nasopharynx: Common Cold

Nasopharyngeal infections caused by viruses produce prominent nasal symptoms and sometimes a scraping sensation in the throat. Approximately 40-50% are caused by Rhinoviruses, and 10% by Coronaviruses.

Oropharynx: Pharyngitis

Infection of the oropharynx, caused by various viruses and bacteria, is associated with throat discomfort, especially during swallowing, and sometimes nasal symptoms.

Larynx and Trachea

• Children: Infection of the larynx and upper airway is associated with Croup, characterized by upper airway obstruction, a barking cough, and difficulty breathing.
• Adults: Hoarseness is the main clinical manifestation of laryngeal infections.

Bronchi and Bronchioles

• Bronchitis: Influenza and many other viruses cause infections at this level.
• Bronchiolitis: Respiratory Syncytial Virus (RSV) causes syncytia (fused cells) and leads to bronchitis, pneumonia, and upper respiratory infections.

Lung Infections: Pneumonia

Pneumonia is an infection of the lung parenchyma with varying clinical manifestations.

Classification of Pneumonia

• Community-Acquired: Transmission from person to person; common in infants.
• Nosocomial Pneumonia: Hospital-acquired infections.

Symptoms and Diagnosis

Common symptoms include fever, malaise, and chest-related signs:

• Chest pain (often pleuritic).
• Cough (with or without sputum).
• If lung involvement is extensive: Diarrhea and rapid breathing.

Note: The most important tool for diagnosis is a chest radiograph.