Respiratory Infections Overview

Respiratory Infections

• Respiratory infections are more frequent than infections of any other organ.
• They account for the most lost workdays in the general population.
• Most upper respiratory tract infections are caused by viruses and are mild.
• Upper respiratory tract locations include nose, larynx, trachea and main bronchi.
• Lower respiratory tract locations include bronchi, lungs and terminal bronchi.

Pathology of Pulmonary Sepsis (Upper Respiratory Tract)

• Nose, sinuses, larynx, and trachea are parts of the upper respiratory tract.
• Common symptoms include time off work, mild, transient, and viral.

Pathology of Pulmonary Sepsis (Lower Respiratory Tract)

• Bronchi, terminal bronchi, and lung parenchyma are part of the lower respiratory tract.
• Lower respiratory infections are often more serious, causing morbidity and mortality.
• These infections are caused by bacteria, viruses, atypical microorganisms, and fungi.
• They are sometimes secondary to irritants.

Respiratory Tract Defenses

• Pneumonia occurs when respiratory tract defenses are impaired.
• Impaired defenses can be due to:
  • Cough reflex impairment (coma, anesthesia, drugs, aspiration)
  • Nasal hair, turbinate, and nasopharynx filtering issues
  • Ciliary apparatus dysfunction (smoke, hot gases, corrosives, viruses)
  • Reduced IgA antibody secretion
  • Decreased alveolar macrophage activity
  • Excessive mucous accumulation (tobacco, smoke, excess oxygen, cystic fibrosis, alcohol)
  • Obstruction by fluid (surfactant, Igs, complement)
  • Impaired cell mediated immunity (chronic diseases, cancer patients, chemotherapy, immune deficiencies, HIV)
  • Viral infections

Respiratory System Infections

• Infections can have several types of origin including primary (viral, bacterial, mycoplasmal, fungal)
• Secondary bacterial infections (following a viral infection)
• Secondary to irritants

Upper Respiratory Tract Sepsis (Viral)

• Common cold is the most common viral upper respiratory tract infection.
• Caused by different rhinovirus serotypes.
• Acute inflammation of the eyes and throat with congestion and watery exudate.
• Secondary bacterial infection can follow, resulting in purulent green discharge.
• Viral sore throat, pharyngitis, and conjunctivitis (caused by adenovirus - 30 serotypes)
• Congestion, watery exudate, and potentially purulent secondary infections.
• Influenza caused by the influenza virus.
• Involves mainly upper respiratory tract.
• Accompanied by fever, lassitude, and depression.
• In a small proportion, can progress to pneumonia.

Upper Respiratory Tract Sepsis (Bacterial)

• Bacterial infections are uncommon in developed countries, but can be secondary to conditions that weaken resistance to infection.
• Include viral infections, chronic bronchitis, and bronchiectasis.
• Bacteria colonizing nose and throat. (e.g., Streptococcal pyogenes, and other bacteria.)
• Acute laryngitis, epiglottitis, and haemopahilus influenzae types B or Streptococcal pyogenes.
• Swollen tissues can make breathing difficult.
• Irritation from pollutants (smoke, corrosives, and noxious gases).

Lower Respiratory Tract Sepsis (Pneumonia)

• Pneumonia is an inflammation of alveolar spaces.
• Host reaction and exudates (polymorphs, fibrin, edema fluid) lead to consolidation.
• Classification of pneumonia based on morphology:
  • Bronchopneumonia
  • Lobar pneumonia
• Radiologically, bronchopneumonia may look confluent or like lobar pneumonia.
• Etiology (causes) of pneumonia and clinical settings.

Bronchopneumonia

• Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus pneumoniae, Klebsiella, Pseudomonas aeruginosa, and coliform bacteria
• Inflammation starts in bronchi.
• Spreads to adjacent alveoli.
• Patchy foci coalesce (join) into consolidation.
• Frequently widespread and bilateral pneumonia.
• Rarely heals with fibrosis.

Lobar Pneumonia

• Characterized by virulent organism, high host vulnerability, and Streptococcus pneumoniae as dominant.
• Inflammation begins in alveoli.
• Exudate flows to bronchioles and alveoli; spreads luminally.
• Polymorphs, fibrin, and edema fluid fill alveoli in all lobes.
• Consolidation occurs across the lobes.
• Often resolves completely.

Pneumonia X-Rays

• X-ray images are used to visualize pneumonia.

Important Treatment Considerations

• Identifying the organism (bacteria, fungi, virus, etc.) is critical.
• Culture and sensitivity testing are needed for appropriate antibiotic selection.

Pneumonia Etiology

• Bacterial
• Fungal
• Viral (see below)
• Aspiration
• Radiation
• Allergic mechanisms

Clinical Settings for Pneumonia

• Community-acquired acute pneumonia (Streptococcus pneumoniae, Haemophilus influenza, Moraxella catarrhalis)
• Gram-negative bacilli (Klebsiella, E. coli, Pseudomonas)
• Staphylococcal aureus (often MRSA) and antibiotic resistance.
• Invasive procedures increase risk.
• Immunosuppressed host (CMV, Pneumocystis carinii, Mycobacterium avium-intracellulare, aspergillosis, candidiasis)

Community-Acquired Pneumonia (CAP)

• Usually follows a viral infection.
• Sudden onset, high fever, chills, pleuritic chest pain, mucopurulent cough.
• More prevalent in those with chronic disease (heart failure, COPD, diabetes), chronic respiratory diseases, or immune deficiency syndromes.
• Lobar or bronchopneumonia.
• Often sputum shows gram-positive diplococci and numerous neutrophils.
• Blood cultures may be positive in 20-30% of patients.
• Usually responds to penicillin, but resistance is increasing.

Pneumonia Complications

• Complete resolution with appropriate antibiotics is common.
• Incomplete resolution is less common.
• Pleural adhesions are the most common complication, particularly with lobar pneumonia.
• Lung abscess can occur.
• Septicemia is an uncommon complication.
• Untreated severe pneumonia can lead to death.

Pneumonia Pleuritis

• Acute pleurisy (inflammation of the lining surrounding the lungs) can result in case of lobar pneumonia.

Viral Pneumonia

• Interstitial pneumonia is common, characterized by interstitial infiltrate, and lymphocytes and histiocytes.
• No alveolar exudate present initially, presenting as atypical pneumonia.
• Generally mild, but can be severe in cases when underlying conditions (debility, alcoholism, immunocompromised individuals) are present.

Pulmonary Tuberculosis

• Caused by Mycobacterium tuberculosis transmitted via droplets.
• Primary tuberculosis, a childhood infection, results in a primary lesion, either a Ghon focus or a Ghon complex.
• These typically heal with fibrosis or calcification.
• Secondary Tuberculosis (previously sensitized; new infection or reactivation of a microbe) usually affects the upper and lower lung lobes.
• It might include foci (lesions) that heal with fibrosis and/or calcification.
• Haemoptysis with erosion of a vessel in the lung might be visible
• Coughing up caseous material might be a sign (cavities may appear in the lung).
• Transmission to other parts of the body (miliary tuberculosis) can occur through lymphatic or blood system spreads.
• Bacteria spreading to hilar lymph nodes might indicate tuberculosis.

Study Guide

• Discuss the defense mechanisms of the respiratory system.
• Discuss the pathogenesis of bronchopneumonia and lobar pneumonia.
• Discuss the morphology of bronchopneumonia and lobar pneumonia.
• Differentiate between viral and bacterial pneumonia.
• Write a short note on pulmonary tuberculosis.

This quiz covers the essential information regarding respiratory infections, focusing on both upper and lower respiratory tracts. Learn about common causes, symptoms, and the implications of these infections on health and work. Test your knowledge on the pathology of pulmonary sepsis and its effects.