Lower Respiratory Tract Infections

Question 1

Death from RTI most commonly occurs from

Answer 1

LRTI

Question 2

What are the LRTI syndromes?

Answer 2

• acute bronchitis
• acute exacerbation of chronic bronchitis
• bronchioloitis
• pneumonia
• lung abcess
• empyema

Question 3

What causes acute bronchitis?

Answer 3

• usually associated with a viral URTI
• dry cough commonly associated with colds that can persist after cold symptoms resolve
• may get pharyngitis, laryngitis as well

Question 4

What conditions comprise COPD?

Answer 4

chronic bronchitis and emphysema

Question 5

What is chronic bronchitis?

Answer 5

• defined as a persistent cough eg 3/months of a year on successive years
• cough must be productive
• indication of chronic lung damage and inflammation

Question 6

Why are COPD and chronic bronchitis pt more susceptible to infection?

Answer 6

• reduced innate immunity
• COPD are usually chronic smokers
  
  • damage to epithelium reduces ability to remove bacteria from the lungs and airways
• as a result, get infections with low-grade URT commensals
  
  • eg pneumococcus and H. influenzae

Question 7

What exacerbates chronic bronchitis?

Answer 7

• URT commensals
• usually pneumococci and/or H. influenzae
• ++sputum production (2 cups from 0.5)
• change in sputum colour
  
  • normally yellow
  • becomes green, lumpy, and may contain blood
• can push them into respiratory failure
• may have fever

Question 8

What causes bronchiolitis?

Answer 8

• occurs almost exclusively <1 yo
• similar symptoms to asthma (expiratory wheeze)
• caused by RSV, especially when epidemic
  
  • thought that maternal Abs cross the placenta, they can engage the RSV that invades the RT epithelium forming immune complexes and a immune reaction in the airways that leads to inflammation and narrowing
  • narrow infant airways thought to play a role
• tends to mostly affect bronchioles (not supported by cartilage)
  
  • on expiration, the inflammation of the airways causes proximal air trapping and expiratory wheese

Question 9

What is the difference between acute bacterial pneumonia and atypical pneumonia?

Answer 9

• acute bacterial pneumonia:
  
  • well people become acutely ill with high fever, consolidation (dull percussion, bronchial breathing)
  • inflammation in the airways, can spread along in lung
  • leakage of neutrophils etc int airways and alveoli
    
    • lobar or bronchopneumonia on x-ray
• atypical pneumonia (‘viral’ pneumonia plus some bacterial causes):
  
  • people get less sick but for longer, slower progression
  • ‘walking pneumonia’
  • inflammation in interstitial tissue
  • patchy consolidation on x-ray

Question 10

What causes acute bacterial pneumonia?

Answer 10

• pneumococcus is #1 cause:
  
  • 80% of community-acquired cases caused by pneumococcus
  • 50% of hospital-acquired cases caused by pneumococcus
• Staphylococcus aureus
• Klebsiella pneumoniae (worse prognosis)
• Legionella
• TB
• Chlamydophila (C. pneumoniae, C. psittaci in birds)

Question 11

Klebsiella pneumoniae

Answer 11

• gram negative rod
• encapuslated, lac fermenting, facultative anaerobe
• normal flora of mouth, skin, intestines
• if aspirated, can cause lobar pneumonia
  
  • worse prognosis than s. pneumoniae (gram positive)

Question 12

Legionella

Answer 12

• gram negative
• L. pneumphila causes Legionnaires disease, a pneumonia type illness

Question 13

What causes atypical pneumonia?

Answer 13

• most common cause is Mycoplasma pneumoniae
  
  • no cell wall; antibiotics have no effect
• Chlamydia trachomatis in newborns and neonates (first month)
• Moraxella catarrhalis
• influenza
• RSV
• adenovirus

**atypical is more common in young than old; typical more common in very young and old**

Question 14

What causes ‘other’ pneumonia?

Answer 14

• histoplasma
• asoergillus
• pneumocysitis jirovecii (carinii) [yeast-like fungus (protozoan)]

Question 15

What causes lung abcesses?

Answer 15

• mixed anaerobes
• with or without Staph or Klebsiella
• usually forms after pneumonia

Question 16

What causes empyema?

Answer 16

• pus in the pleural space
• staph aureus, secondary to pneumonia

Question 17

How is pneumonia diagnosed?

Answer 17

• clincial features
  
  • can distinguish typical from atypical
• radiological feautres
• lab techniques

Question 18

What are the important clincial considerations in pneumonia diagnosis?

Answer 18

• community (80% pneumococcus) or hospital (50% likely pneumococcus) acquired
• severity index - used in antibiotic guidelines for tx
• underlying illness: COPD, AIDS, CF
• other risk factors:
  
  • occupational
    
    • contact with animals (C. psittaci), hides (anthrax spores cause mediastinal infections), air conditioning (L. pneumophili breeds amoebae in cooling towers, survive similarly in human macrophages), soils (L. longbeachiae)
  • travel
    
    • fungal pneumoniae (southern USA)
  • homelessness
    
    • mycobacterial infection, alcohol intake related to klebsiella infections

Question 19

What type of specimen is collected for laboratory diagnosis of pneumonia?

Answer 19

• properly collected sputum, not throat swab
  
  • ie few/no buccal epithelial cells on gram stain
  • looking for G+ diploccoci (pneumococci in pairs, short chains) with a pointed shape in predominant culture
    
    • G- pleiomorphic rods would suggest H. influenzae (also found in CSF in meningitis)
• transtracheal aspirate (USA)
  
  • tube thru cricothyroid membrane into the area below the larnyx (should be sterile)
• aspiration via tracheostomy (if tracheo or endotracheal tube already in place) or bronchoscope
  
  • both may be contaminated by commensals from above epiglottis
• pleural tap (if there is an effusion e.g. empyema)
• lung biopsies (needle under X-ray guidance or open) if do not respond to tx
• blood culture and serology in adults (if found in blood, will be cause)

Question 20

Serological diagnosis of pneumonia is useful for

Answer 20

organisms that are hard to culture, ie:

• Mycoplasma pneumoniae
• Legionella pneumoniae
• Chlamydophila and Chlamydia species
• Coxiella burnetti (cattle and sheep)

Question 21

Serological diagnosis of pneumonia can differentiate recent infection from previous exposure by

Answer 21

• Looking for a specific IgM or a rising titre

Question 22

Antigen detection in serological diagnosis of pneumonia is used for

Answer 22

• detection of common causative organisms by their antigens
  
  • common viruses
  • Bordetella
  • Legionella pneumophila type I
    
    • from urine (Ag is concentrated here)
• sample obtained by nasopharyngeal aspirate
• stain slide with most common causative agent antibodies circulating at that time (influenza A, B, parainfluenza viruses 1, 2, and 3, Bordatella pertusis [whooping cough], RSV, coronaviruses, etc.)

Question 23

Why is a specific diagnosis important in pneumonia?

Answer 23

• for appropriate antibiotic Rx
• for must-know pathogens:
  
  • pandemic potentials e.g. SARS, MERS, H5N1, H7N9
  • Legionella spp to shut down contaminated air cooling units
  • bioterorrism agents (anthrax, plague)
  • community acquired MRSA
    
    • becoming a more important cause of pneumonia
    • bad prognosis, specific treatment
• for should-know pathogens:
  
  • penicillin-resistant s. pneumoniae
  • gram negative rods that cause pneumonia eg pseudomonas aeruginosa

Question 24

What is the treatment of pneumonia?

Answer 24

• community acquired:
  
  • beta lactam + another drug that is not a beta lactam:
    
    • penG/amoxycillin (bactericides) + doxycycline/macrolide (bacteriostatics)
    • penG and amoxycillin target the pneumococcus
    • doxycyclines and macrolides combat atypical organisms (mycoplasmas, chlamydophilas, legionellae, coxiella)
      
      • all unrelated, but susceptible to macrolides and tetracyclines and resistant to beta lactams
      • tf using both covers virtually all causative pathogens
  • if severe (Klebsiella) add a G- rod antibiotic e.g. gentamicin
  • modify tx to specific risk factors, severity, and known cause (if established)
• hospital acquired:
  
  • depends on severity and risk group

Question 25

What vaccines can prevent pneumonia?

Answer 25

• influenza (not directly, as a risk factor for pneumonia)
• pneumococcal vaccines
  
  • 23-valent polysaccharide (adults)
  • 13-valent conjuage (children)
    
    • cannot mount appropriate immune response to the 23v vaccine
• specialized vaccines for high-risk groups