Pneumonia & Acute Bronchitis: Lower Respiratory Tract Infections

• Pneumonia is an infection of the lung tissue causing inflammation in the alveolar space, identifiable as a consolidation on a chest x-ray.
• Acute bronchitis is an infection and inflammation of the bronchi and bronchioles.
• Pneumonia and acute bronchitis are lower respiratory tract infections, whereas upper respiratory tract infections (e.g., common cold) are generally viral.
• Lower respiratory tract infections have a higher likelihood of being bacterial.

Classification

• Community-acquired pneumonia (CAP) develops in the community.
• Hospital-acquired pneumonia (HAP) develops after more than 48 hours in a hospital.
• Ventilator-acquired pneumonia (VAP) develops in intubated patients in the intensive care unit.
• Aspiration pneumonia results from aspirating food or fluids, commonly in patients with impaired swallowing, and is associated with anaerobic bacteria.

Presentation

• Presenting symptoms of pneumonia include cough, sputum production, shortness of breath, fever, feeling generally unwell, haemoptysis, pleuritic chest pain, and delirium.
• Characteristic chest signs include bronchial breath sounds, focal coarse crackles, and dullness to percussion.
• Bronchial breath sounds (harsh inspiratory and expiratory breath sounds) are due to consolidation around the airways.
• Focal coarse crackles are caused by air passing through sputum in the airways.
• Dullness to percussion is due to lung tissue filled with sputum or collapsed
• Deranged basic observations such as tachypnoea, tachycardia, hypoxia, hypotension, fever, and confusion can indicate sepsis secondary to pneumonia.

Severity Assessment

• NICE guidelines (updated 2022) recommend the CRB-65 scoring system out of hospital and the CURB-65 in hospital, suggesting hospital assessment for CRB-65 scores over 0.
• The CURB-65 criteria include: Confusion, Urea > 7 mmol/L, Respiratory rate ≥ 30, Blood pressure < 90 systolic or ≤ 60 diastolic, and Age ≥ 65.
• The CURB-65 score predicts mortality and is categorised as low risk (0/1), intermediate risk (2), and high risk (3-5).
• A CURB-65 score of 0/1 suggests considering treatment at home, ≥ 2 suggests considering hospital admission, and ≥ 3 suggests considering intensive care.
• NICE state a CURB-65 score of 0/1 is low risk (under 3% mortality), 2 is intermediate risk (3-15%), and 3-5 is high risk (above 15%).

Causes

• The most common cause of typical bacterial pneumonia is Streptococcus pneumoniae.
• Other causes include Haemophilus influenzae.
• Moraxella catarrhalis is common in immunocompromised patients or those with chronic pulmonary disease.
• Pseudomonas aeruginosa affects patients with cystic fibrosis or bronchiectasis.
• Staphylococcus aureus is seen in patients with cystic fibrosis.
• Methicillin-resistant Staphylococcus aureus (MRSA) is common in hospital-acquired infections.

Atypical Pneumonia

• Atypical pneumonia is caused by organisms that can’t be cultured or detected using a gram stain and do not respond to penicillin.
• Atypical pneumonia is treated with macrolides, fluoroquinolones, and tetracyclines.
• Legionella pneumophila (Legionnaires’ disease) is caused by inhaling infected water and can cause SIADH, resulting in hyponatraemia.
• Mycoplasma pneumoniae causes milder pneumonia and erythema multiforme, and can cause neurological symptoms in young patients.
• Erythema multiforme is characterised by varying-sized “target lesions” formed by pink rings with pale centres.
• Chlamydophila pneumoniae causes mild to moderate chronic pneumonia and wheezing in school-age children.
• Coxiella burnetii, or Q fever, is linked to exposure to animal bodily fluids.
• Chlamydia psittaci is contracted from contact with infected birds.
• Mnemonic for atypical pneumonia causes: "Legions of psittaci MCQs" - Legionella pneumophila, Chlamydia psittaci, Mycoplasma pneumoniae, Chlamydophila pneumoniae, Q fever (Coxiella burnetii)

Other Causes

• Pneumocystis jirovecii pneumonia (PCP) is a fungal pneumonia in immunocompromised patients.
• Patients with poorly controlled HIV and a low CD4 count are at high risk.
• PCP presents with dry cough, shortness of breath on exertion, and night sweats.
• Co-trimoxazole treats PCP, and prophylactic co-trimoxazole is prescribed for patients with a low CD4 count.
• The COVID-19 virus (SARS-CoV-2) can cause pneumonia, with symptoms varying greatly.
• Anosmia (loss of smell) is a diagnostic clue.
• Patients may experience silent hypoxia.
• Covid-19 pneumonia treatment involves respiratory support, dexamethasone, and monoclonal antibodies.
• Vaccination has dramatically reduced the number of severe Covid-19 infections.

Investigations

• Patients with CRB 0 or 1 pneumonia may not need investigations.
• A point-of-care CRP test can guide diagnosis and antibiotic use in primary care.
• Hospitalized patients should have a chest x-ray, full blood count, renal profile, and C-reactive protein test.
• Patients with moderate or severe infection should also have sputum cultures, blood cultures, and Pneumococcal and Legionella urinary antigen tests.
• White blood cells and CRP levels rise in proportion to the severity of the infection.
• CRP levels start rising 6 hours behind inflammation and peak after 24-48 hours.

Antibiotics

• Antibiotic treatment should follow local area guidelines.
• Local area guidelines are developed by looking at the antibiotic resistance of the bacteria in the local area and are specific to the local population.
• Mild community-acquired pneumonia is treated with 5 days of oral antibiotics like amoxicillin, doxycycline, or clarithromycin.
• Moderate or severe pneumonia is treated initially with intravenous antibiotics, later switched to oral antibiotics as the condition improves, along with respiratory support.

Complications

• Complications of pneumonia include sepsis, acute respiratory distress syndrome, pleural effusion, empyema, lung abscess, and death.