Lower Respiratory Tract Infections Overview

Lower Respiratory Tract Infections (LRTIs)

• LRTIs affect the airways and lungs, distinct from URTIs affecting the nose, sinuses, ears, and throat.
• Typical causative organisms include Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus, Mycoplasma pneumoniae, Legionella, other Gram-negative bacilli (Pseudomonas, Klebsiella), fungi, and viruses (adenovirus, influenza).

LRTI Infections: Acute

• Pneumonia: Inflammation of air sacs in the lungs. Types include community-acquired (CAP), hospital-acquired (HAP), aspiration pneumonia.
• Acute Bronchitis: Inflammation of the trachiobroncheal tree, usually viral but can be secondary bacterial infection (Streptococcus pneumoniae or Haemophilus influenzae). Treatment is symptomatic.
• Acute Bronchiolitis: Primarily caused by respiratory syncytial virus (RSV), affecting children under 2 years. Treatment is symptomatic, plus possible hospitalization.
• Whooping Cough (Pertussis): Caused by Bordetella pertussis, a notifiable disease. Characterized by catarrhal illness progressing to a dry, non-productive cough with a "whoop" sound. Treatment is typically Clarithromycin (Erythromycin for pregnancy).

LRTI Infections: Chronic

• Tuberculosis: Chronic lung infection.
• Aspergillosis: Fungal infection of the lungs.
• Lung Abscesses: Localized pus-filled pockets in the lungs.
• Empyema: Pus in the pleural space surrounding the lungs.
• Infections in Cystic Fibrosis Patients: Recurring infections, often with Pseudomonas aeruginosa, difficult to eradicate.

Investigations for LRTIs

• Bronchitis: Investigations less common, as organism sensitivities are usually known.
• Pneumonia: Chest X-ray, sputum culture, and laboratory tests are often indicated.

Pneumonia: CAP vs HAP

• CAP: Illness originates outside a healthcare setting.
• HAP: Develops 48-72 hours after hospital admission. Can include a wider range of bacteria, including more opportunistic ones (Pseudomonas aeruginosa, Klebsiella pneumoniae), and antibiotic resistance is a potential concern, but similar bacteria to CAP can cause it.
• Risk Factors for HAP: Mechanical ventilation over 48 hours; ICU stay, longer hospital stays, comorbidities (immunocompromised, elderly, diabetic, COPD), and conditions that impair the gag reflex (brain injury).

Pneumonia: Causative Organisms

• Bacteria (most common): Streptococcus pneumoniae, Haemophilus influenzae, Klebsiella pneumoniae, Pseudomonas.
• Mycoplasma pneumoniae and Legionella pneumophila (Atypical pneumonia, are common, but don't have a cell wall, making b-lactam antibiotics ineffective).

Diagnostic Tools: Pneumonia

• Cultures: Pleural fluid, sputum, blood, and urine samples. Important to note potential for antibiotic influence on results.
• Serological tests: For atypical pneumonias (e.g., Mycoplasma pneumoniae, Legionella pneumophila).

CAP Diagnosis and Severity Assessment

• Diagnosis: Symptoms of LRTI (cough and other respiratory symptoms), new focal chest signs, systemic features (fevers, sweats, rigors).
• CURB-65: A clinical score used to assess severity in community-acquired pneumonia. Components: Confusion, BUN, Respiratory rate, Blood pressure, Age.

CAP Treatment

• Penicillin allergy: Doxycycline or Clarithromycin.
• Course of antibiotics essential to complete. Patient should stay hydrated, ensure rest, and the cough may endure for a couple of weeks.

HAP Treatment

• Non-severe: Oral amoxicillin, metronidazole, review within 48hrs.
• Severe: IV co-amoxiclav. Add anti-pseudomonal antibiotics when needed (e.g., Ceftazidime), Flucloxacillin for Staphylococcus aureus.

Atypical Organisms (Pneumonia)

• Mycoplasma pneumoniae ("walking pneumonia") - mild, gradual onset. Treated with macrolides or fluoroquinolones.
• Legionella pneumophila (Waterborne outbreaks): Requires specific treatment, such as quinolones (Levofloxacin) or macrolides (Azithromycin) (with or without rifampicin) and system decontamination.

Chronic LRT Infections

• Cystic Fibrosis: Viscous secretions leading to persistent infections requiring specialized management. Pseudomonas is common, although others (Staphylococcus aureus and Haemophilus influenzae).

Clinical Case: Mrs. G (Possible CAP)

• Symptoms suggest CAP – high fever, cough, feeling unwell.
• Possible causative organisms for CAP include Streptococcus pneumoniae, Haemophilus influenzae, atypical bacteria (Chlamydophila pneumoniae, Mycoplasma pneumoniae), Moraxella catarrhalis, Staphylococcus aureus, influenza viruses, and fungi.
• Investigation points: Chest X-ray, sputum culture, lab tests, CURB-65 scoring.
• Mrs. G’s examination demonstrates temperature, heart rate, BP, and respiratory rate indicative of possible CAP. The penicillin allergy and occasional smoking are considerations. A CURB-65 assessment determines severity.

Vaccination

• High risk patients such as Mrs. G (65 years old) should prioritize annual flu vaccination, plus once only pneumococcal vaccination.