L5: Fever and cough - pneumonia Flashcards
Bronchitis
- S. pneumoniae does not cause bronchitis (mainly viral causes)
- Antibiotics only useful in early stages of pertussis
- Cough, fever, sometimes sputum
- Benign, self-limiting
- Does not cause SOB, hypoxia
Pneumonia in elderly
- Tachypnoea in 70% (to increase ventilation, nociception)
- Crackles in 80%
- Consolidation (bronchial breathing, dull percussion) in 30%
- Fever, chills in 50%
- Non-pulmonary in 20%
Pneumonia risk factors
- Age <2 or >65
- Chronic lung disease e.g. CF
- Smoking
- Immune dysfunction
Epidemiology of pneumonia
- Most common serious bacterial infection
- Most common in elderly, young children
- In adults, elderly more common in winter
- Bacterial 90%, viral 10%
Causative bacteria of pneumonia
Streptococcus pneumoniae 70% (1/2-2/3)
Haemophilus influenza
S. aureus
Viral cause (esp. influenza)
Streptococcus pneumoniae colonisation
- Alpha-haemolytic (viridans group - do not usually cause disease and if they do then endocarditis except S. pneumoniae causes disease e.g. pneumonia, meningitis, spontaneous peritonitis and septic arthritis)
- Colonise nasopharynx (10% adults, 30% children)
- Prevalence of colonisation increases in winter
- In adults colonisation persists for a few weeks
Strep. pneumoniae - virulence factors
- Polysaccharide capsule prevents phagocytosis, complement binding
- Pneumolysin (toxin) lyses neutrophils, epithelial cells
- Choline binding protein binds to Ig receptor on epithelial cells and allows entry into cells
- Pneumococcal surface protein A (PspA) binds epithelial cells, prevents C3b deposition
- Pili help colonisation and cytokine production
- PspC prevents complement activation
Invasive pneumococcal disease
High in infants/young children, rare in middle age, high in elderly
More cases in winter months
Investigations
- CXR
- Sputum sample (yield dependent on quality of sample): PCR to test for viruses and cultures for bacteria
- Blood count (expect high WBCs, neutrophilia - not very useful)
- Serology (antibodies, takes a few wks for antibodies but can be used where hard to culture)
- Streptococcal urinary antigen test (detect antigens, lacks sensitivity - if positive helpful, but if negative could just be too low in urine)
- Nasopharyngeal swab: viral PCR (useful in hospital setting)
- Blood cultures (low yield)
Treatment of pneumonia
Antibiotics (required and effective - reduced duration of illness and risk of death)
Antibiotics for S. pneumoniae, Haemophilis influenzae and S. aureus
Antibiotics and pneumonia
- Penicillin resistance is increasing (altered transpeptidase -> less binding affinity of penicillin (e.g. S. pneumoniae has reduced susceptibility)
- Oral dosing may be inadequate, IV dosing will work (impt to consider when treating meninigitis caused by S. pneumoniae)
- Can use oral antibiotics with excellent activity against penicillin resistant pneumococci e.g. quinolones, recently developed macrolides, ketolides
Antibiotics - ribosome targets
- Antibiotics often target bacterial ribosomes
- Macrolides antibiotics bind at transpeptidation site (bacteriostatic)
- Aminoglycosides block initiation site
Macrolide antibiotics - use and adverse effects
e. g. erythromycin, clarithromycin, azithromycin (treats chlamydia)
- Broad spectrum
- Active against streptococci, staphylococci (limited activity against gram neg)
- Used in skin infections if allergic to penicillin
Adverse effects: erythromycin gives GI upset (agonist of motilin receptor in gut), sudden death (class effect - prolongs QT interval, v. rare), drug-drug interactions
Empiric treatment of community-acquired pneumonia
Based on severity, usually 5 days
Mild: amoxycillin
Moderate: amoxycillin + roxithromycin
Very sick: amoxycillin/clavulanic acid + erythromycin
Treatment of healthcare-associated pneumonia
Cefuroxime +/- gentamicin
