JC14 (Medicine) - Lower respiratory tract infections Flashcards
Define pneumonia
inflammation of lung parenchyma, commonly due to infective agents
Typical clinical picture of acute pneuomia
Symptoms:
Systemic: fever, rigors, shivering, malaise, headache, ↓appetite, ± delirium
Pulmonary:
→ Cough: short, painful, dry (initial) → productive with mucopurulent sputum ± haemoptysis (later)
→ Pleuritic chest pain when visceral pleura is involved
→ Dyspnoea
Others:
→ Upper abdominal tenderness if lower lobe pneumonia or associated hepatitis
Explain how pneumonia leads to dyspnea and pleurisy
Pathological: form of acute respiratory infection that alveoli are filled with pus and fluid, making breathing painful and limits O2 intake
Classify pneumonia by anatomical regions involved
Anatomical:
→ Lobar pneumonia: homogeneous consolidation of ≥1 lobes
→ Bronchopneumonia: more patchy alveolar consolidation a/w bronchial and bronchiolar inflammation
Classify pneumonia by aetiological organisms (3)
Aetiological: bacterial, viral, fungal
Types of pneumonia (5)
→ Community-acquired pneumonia (CAP)
→ Hospital-acquired pneumonia (HAP)
→ Ventilator-associated pneumonia
→ Aspiration pneumonia
→ Pneumonia in immunocompromised patients
List causative bacteria of Community acquired pneumonia
Gram +
- Streptococus pneumoniae*
- Haemophilus influenzae non-typeable*
Atypical
- Mycoplasma pneumoniae, Chlaymdophila pneumoniae, Legionelaa pneumophila
(Gram -)
Klebsiella pneumoniae
Pseudomonas aeruginosa
List causative bacteria of hospital acquired pneumonia
Gram +
- Streptococus pneumoniae*
- Haemophilus influenzae non-typeable*
- Methicillin-resistance staphylococcus aureus (MRSA)
Gram -
- Klebsiella pneumoniae ***
- Pseudomonas aeruginosa ***
Anaerobes
- Bacteroides species
List causative bacteria of aspiration pneumonia
Gram -
- Klebsiella pneumoniae *
- Pseudomonas aeruginosa *
- Other nosocomial gram - bacteria
Anaerobes
- Bacteroides species **
Typical PE signs of lobar pneumonia
□ Vitals: fever, ↓BP, ↑HR, ↑RR, ± ↓SpO2
□ Chest
→ Decrease air entry
→ Coarse crackles
→ Consolidation signs: percussion dullness, bronchial breath sounds, ↑vocal resonance
Baseline investigations for suspected pneumonia **
- CXR
- gold-standard for CAP diagnosis
- clinical suspicious with negative CXR > CT/MRI - Blood (severity)
- CBC with WBC differential
- RFT
- LFT
- ESR/CRP
- Arterial blood gas - Microbiology
- Sputum: gram stain, C/ST
- Blood: culture and serology
- Nasopharyngeal aspirate: RAT for influenze, PCR for virus, M. pneumoniae
- Urine: RAT for Legionella, S. pneumoniae
- BAL/ Transbronchial biopsy, thoracoscopic biopsy
Describe atypical pneumonia syndrome
□ Cause: usually refers to M. pneumoniae, C. pneumoniae and L. pneumophila
□ Characterized by:
→ Symptomatology: less severe, prominent systemic complaints
→ Ix: relatively normal WBC counts (vs neutrophilia in typical bacterial pneumonia
Clinical approach to pneumonia
- Diagnosis of CAP
- Assessment of severity
- Empirical treatment based on:
Likely causative pathogens
Clinical severity
Ddx of pneumonia
- Pulmonary oedema
- Pulmonary/pleural TB
- Eosinophilic pneumonia
- Bronchoalveolar carcinoma
- Cryptogenic organizing pneumonia (rare)
Typical RFT and LFT results for community-acquired pneumonia
□ RFT: ↑urea*, hypoNa*, renal dosing of Abx
□ LFT: liver involvement (in basal pneumonia), ↓Alb*
List all samples needed for microbiological diagnosis of pneumonia
- Sputum: gram stain, C/ST
- Blood: culture and serology
- Nasopharyngeal aspirate: RAT for influenze, PCR for virus, M. pneumoniae
- Urine: RAT for Legionella, S. pneumoniae
- BAL/ Transbronchial biopsy, thoracoscopic biopsy
Most common pathogen causing acute CAP in elderly
Strep. pneumoniae (most common)
Haemophilus pneumoniae
Klebsiella pneumoniae (esp. DM, alcoholic)
Most common pathogen causing acute CAP in the young
Mycoplasma pneumoniae
Streptococcus pneumoniae
Complications of mycoplasma pneumoniae infection
haemolysis (60%), cold agglutinin disease, erythema multiforme, encephalitis
Complications of Klebsiella pneumoniae infection
UTI and renal abscess, liver abscess, endophthalmitis
Typical route of spread for Legionella pneumophila
from aqueous environment (water tanks, cooling towers, spas…)
Route of infection: breathe in contaminated droplets and mists from artificial water systems (eg. hot water baths) or handle garden soils, compost, potting mixes
Typical presentation of Legionella pneumophila infection
S/S: classically prodromal flu-like S/S with CNS (confusion) and GI (diarrhea) involvement
Specific investigations and diagnostic tests for Legionella pneumophila infection
→ Bloods: classically lymphopenia w/o marked leukocytosis, T1RF, SIADH, dLFT
→ CXR: lobar or multilobar consolidation
→ Microbiology: G- bacillus not well-visualized on Gram stain (WBC++ no organisms), culture require special selective media and takes 1-3w → usually diagnosed by urine antigen test (for serotype 1)
Typical viruses that cause acute CAP
influenza, parainfluenza, RSV, measles*
More common in children than adults
Specific pathogen that cause opportunistic infection and pneumonia in HIV patients
Pneumocystis jirovecii
patients with HIV or severe immunocompromised state (eg. post-chemo)
Criteria for assessment of clinical severity of CAP
CURB-65
Confusion
Urea > 7mmol/L
Respiratory rate > 30/min
Blood pressure: SBP < 90 or DBP <60
Age > 65
0 or 1 = home treatment
2 or more factors = immediate hospital admission
3 or more = ICU
Outline management of CAP
- Oxygen therapy
- all patients with resp. failure
- Target SaO2 > 92%
- High concentration oxygen/ CPAP/ Mechanical ventilation - Fluid rehydration
- Antibiotics coverage
- Analgesia for pleuritic pain
- simple analgesics - Manage complications
Antibiotics coverage for CAP
- Timing
- Coverage
- Choice of antibiotics
- Admin within 6-8 hours, duration 7-10d
- All CAP needs Strep. pneumoniae coverage; All severe CAP needs Legionella pneumophila coverage
Typical pathogen:
□ Penicillin + β-lactamase inhibitor → Eg. augmentin
Atypical pathogens:
□ ± macrolide or tetracycline
→ Eg. clarithromycin (klacid), azithromycin, doxycycline
Risk factors for multi-drug resistant pathogens causing CAP
□ Recent or frequent Abx use
□ Recent or frequent hospitalization
□ Nursing home resident
□ Immunocompromised state
Choice of antibiotics for:
- Outpatient CAP
- Moderate inpatient CAP
- Severe inpatient CAP
- Outpatient CAP
PO amoxicillin-clavulanate (Augmentin) ± macrolide or doxycycline - Moderate inpatient CAP
PO/IV amoxicillin-clavulanate (Augmentin) ± macrolide or doxycycline
Alternatives: IV ceftriaxone or cefotaxime ± macrolide or doxycycline - Severe inpatient CAP
IV piperacillin-tazobactam (Tazocin) or ceftriaxone or cefepime ± macrolide or doxycycline
Follow-up for CAP
Chest physiotherapy: helps expectoration
clinical review 6 weeks later
CXR if persistent S/S or suspect underlying malignancy
Possible ddx for delayed recovery from CAP
→ Complications, eg. abscess, parapneumonic effusion
→ Alternative dx, eg. ILD, TB
→ Underlying cause, eg. obstruction, recurrent aspiration
Complications of CAP
□ Respiratory failure
□ Lung abscess
□ Pathogen Spread:
→ Septicaemia with multi-organ failure
→ Parapneumonic effusion
→ Empyema thoracis
□ Systemic effects:
→ Electrolyte abnormalities, eg. hypoNa due to SIADH
→ Cardiac complications: acute MI, cardiac arrhythmia (esp AF)
Causes of recurrent CAP
→ Underlying structural disease, eg. bronchial obstruction, bronchiectasis
→ Host factors, eg. recurrent aspiration, immunocompromised state
Define Hospital-Acquired Pneumonia (HAP)
Typical route of infection?
pneumonia occurring ≥48h after hospitalization + excluding incubating infection at admission
aspiration of oropharyngeal secretions colonized by hospital-acquired organisms
Predisposing factors of HAP
□ General debility and old age
□ Smoking and COPD
□ ↑risk of aspiration: post-GA, nasogastric tube
□ ↓gastric aciditiy: antacids, H2 blockers (↑GI colonization)
□ Mechanical ventilation (ventilator-associated pneumonia (VAP))
Typical bacteria causing HAP
□ Early onset (<4-5d of admission): similar to CAP
□ Late-onset:
→ Gram - bacilli, eg. Escherichia, Klebsiella spp
→ Non-fermenters, eg. Pseudomonas, Acinetobacter baumanii
→ Multi-resistant bacteria, eg. MRSA
→ Anaerobes, eg. Bacteroides
Empirical treatment for HAP
Early onset:
3rd generation cephalosporin
OR
β-lactam/β-lactamase inhibitor (Augmentin, Unasyn)
Late onset:
Anti-pseudomonal β-lactam/β-lactamase inhibitor (Tazocin) OR
Anti-pseudomonal cephalosporin (Cefepime [4G]) OR
Anti-pseudomonal carbapenem (imipenem, meropenem)
± aminoglycoside OR fluoroquinolone
± vancomycin after careful assessment of indications
Define aspiration pneumonia
pneumonia due to aspiration of a relatively large amount of material
Predisposing factors of aspiration pneumonia
□ Impaired gag reflex: ↓GCS, alcoholism, bulbar palsy, vocal cord palsy, terminal illness
□ Regurgitation/vomiting: dysphagia and oesophageal diseases, vomiting, drowning
□ Others: severe dental infection or URTI, tracheo-esophageal fistula
Causative agents of aspiration pneumonia
□ Chemical pneumonitis due to aspiration of acidic materials
□ Infection by oropharyngeal flora
→ Anaerobes, eg. Bacteroides, Porphyromonas, Prevotella, Fusobacterium
→ Others: Streptcoccus, S. aureus, G- bacilli
Investigations for aspiration pneumonia
□ CXR: consolidations, usually in dependent parts of lungs
→ Lower lobes (classically recurrent RLL pneumonia)
→ Posterior segments of upper lobe (if recumbent)
□ VFSS for swallowing problems
→ Follow-up CXR shows contrast medium in lung fields
Management of aspiration pneumonia
□ Treatment of underlying conditions
□ Abx to cover oropharyngeal flora: augmentin ± metronidazole
□ Non-oral feeding (eg. PEG tube, NG tube) → prevent further aspiration
Diagnostic tests of influenza
Rapid antigen test on nasopharyngeal aspirate
RT-PCR
Viral Culture
Serology
Influenza
- Incubation period
- S/S
Incubation period: 1-4 days
□ Systemic: fever (37.8-40oC), myalgia, arthralgia, malaise
□ URTI: running nose, sore throat, cough, sputum
List major influenza types in humans, avians and swines
Notable influenza types:
Human: H1N1 (Spanish), H2N2 (Asian), H3N2 (Hong Kong)
Avian: H5N1, H7N7, H7N9
Swine: H1N1
Extra-respiratory manifestations of influenza infection
Pneumonia: primary viral or superimposed bacterial (S. pneumoniae, S. aureus, esp >65y)
GI involvement: vomiting, diarrhea
CNS involvement: encephalitis, transverse myelitis, aseptic meningitis, GBS
Others: myositis, myocarditis, pericarditis, Reye’s syndrome
Management of influenza infection
□ General: personal hygiene, symptomatic Tx, droplet precaution
□ Neuraminidase inhibitors: effective in both flu A/B
Examples: oseltamivir (Tamiflu, PO 75mg BD x5d), zanamivir (Relenza, 10mg BD inhaler puff x5d)
MoA: inhibit neuraminidase → cannot cleave sialic acid on cell surface → interfere with release of progeny → decrease viral propagation
Define bronchiectasis
pathological dilatation of bronchi
Causes of bronchiectasis
□ Congenital:
→ Cystic fibrosis (rare in Chinese)
→ Ciliary dysfunction: eg. ciliary dyskinesia, Kartagener syndrome
→ Predisposition to infections (eg. 1o hypoγglobulinemia)
□ Acquired:
→ Previous infections, eg. TB, suppurative pneumonia, childhood measles or pertussis
→ Obstruction, eg. foreign body, tumours
→ Rhuematic disorders, eg. RA, Sjogren’s syndrome
→ Gastro-esophageal reflux (leading to chronic aspiration)
→ Lung fibrosis (leading to traction bronchiectasis)
Typical symptoms of bronchiectasis
Chronic course (years) with acute infective exacerbations
- Cough (98%): chronic, persistent
- Daily sputum production (78%): copious, tenacious, purulent, foul-smelling
- Haemoptysis (27%): only streaks of blood
- Exertional dyspnoea ± wheezes
- Pleuritic pain
- Systemic symptoms: weight loss, fatigue, anorexia
Signs of bronchiectasis on PE
□ General: cachexia, clubbing, halitosis
□ Varies with severity:
- Coarse crackles that disappear/change in quality after coughing
- Obstructive pattern → ↓breath sounds, ↓chest wall movement
- Chronic localized fibrosis → bronchial breath sounds
- Cor pulmonale (↑JVP, peripheral oedema, hepatic congestion, parasternal heave, loud P2)
- Respiratory failure (central cyanosis)
Ddx bronchiectasis
COPD: also with recurrent bouts of dyspnoea, productive cough, wheezes, coarse crackles
Asthma: also with recurrent exacerbation of dyspnoea, productive cough and wheezes
Lung fibrosis: also with dyspnoea, cough, crackles and finger clubbing
Typical radiological features of bronchiectasis on CXR
CXR: only abnormal in 50%
→ Ring shadows: dilated bronchi seen from front
→ Tramline shadows: dilated bronchi seen from side (usually in lower lobes)
→ Tubular shadows: dilated bronchi filled with secretions
→ Cystic dilatation ± fluid levels in severe cases
Typical radiological features of bronchiectasis on HRCT
1) Thickened, dilated airways (ring shadows)
- Wider than accompanying arterioles (signet ring sign)
- No peripheral tapering with visible peripheral airway ≤1cm of pleural lining
2) Mucus plugging (darker than airway wall):
- Air-fluid levels visible within cystic dilatation of airway
- Tree-in-bud appearance when peripheral airways are involved
3) Atelactasis, consolidation, abscesses
5 specific diagnostic tests for underlying cause of bronchiectasis
→ Immunoglobulins and neutrophil function test for immunodeficiency
→ Auto-Ab (eg. RF) for autoimmune diseases
→ Ba studies or 24h oesophageal pH monitoring for aspiration causes
→ Ciliary and sperm analysis for primary ciliary dyskinesia
→ Sweat test for cystic fibrosis
Causes of acute exacerbation of bronchiectasis
Treatment
Potential organisms: H. influenzae, S. aureus, P. aeruginosa (if long-standing)
□ Choice of Abx:
→ Anti-pseudomonal penicillins (first-line), eg. piperacillin-tazobactam (tazocin)
→ 3rd and 4th generation cephalosporin, eg. ceftazidime
→ Carbapenems, eg. meropenem, imipenem
→ Aminoglycosides, eg. amikacin
→ Fluoroquinolones, eg. levofloxacin
□ Duration: recommend 14 days
Long-term management of bronchiectasis
□ Treatment of underlying aetiology, eg. GERD, immunodeficiency
□ Long-term (≥3mo) antibiotics for immunomodulatory effect to decrease exacerbations
- Oral Macrolides
□ Airway clearance:
- Chest physiotherapy
- Expectorant or mucolytic
□ Adjuncts:
- Bronchodilators (esp β-agonist): for SOB and obstructive pattern, bronchospasm
- Inhaled corticosteroids (not routine)
□ Surgery (rare)
→ Excision of bronchiectactic areas (eg. lobectomy)
→ Percutaneous embolization of bronchial vessels
