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Respiratory Medicine > Infections of the Lower Respiratory Tract > Flashcards

Infections of the Lower Respiratory Tract Flashcards

1
Q

What are the main LRTIs?

A
  • Bronciolitis
  • Bronchitis
  • Acute exacerbations of COPD
  • Bronchiectasis
  • Community acquired pneumonia
  • Healthcare acquired pneumonia
  • Pulmonary tuberculosis
  • Aspiration pneumonia
  • Empyema
  • Lung abscess
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2
Q

What are the 3 main routes of pathogenesis of LRTIs?

A

1) Bacterial or viral transmission, 2) Impaired host defences, 3) Virulence factors of bacteria and viruses

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3
Q

What are the routes of transmission of LRTIs?

A

1) From the upper respiratory tract – lower respiratory tract is normally sterile, so with reduced host defences infections can occur e.g. S.pneumonia, H.influenzae, M.catarrhalis
2) By airborne route, directly or indirectly
3) Contact with animals or animal products e.g. Coxiella burnetti

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4
Q

What are the host defences in the respiratory tract?

A
  • Nasopharyngeal filtration
  • Mucosal adherence
  • Lysozyme, protease, lactoferrin present in respiratory secretions
  • Cough, gag, sneeze
  • Muco-ciliary clearance
  • Immunoglobulins
  • Complement
  • B&T lymphocytes
  • Alveolar macrophages
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5
Q

How can a host’s defences be reduced?

A

Ventilated patients - Bypassed nasopharyngeal filtration, bypassed gag and coughing reflex, reduced mucociliary clearance
Smokers - Mucosal adherence not as effective, mucociliary function impaired
Immunocomprimised patients

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6
Q

What are the virulence factors of S. pneumoniae and H. influenza?

A

They produce an enzyme IgA protease capable of disabling mucosal IgA, and have polysaccharide capsules which render them resistant to phagocytosis.

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7
Q

What are the virulence factors of B. pertussis?

A

They produce exotoxins which produce widespread local damage

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8
Q

What is the main pathogen of bronchioloitis?

A

Respiratory syncytial virus - RSV

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9
Q

Who is RSV particularly relevant to?

A

Infants in the first 6 months of life

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10
Q

How does bronchiolitis present?

A

Starts with cold like symptoms e.g. nasal discharge

Followed by fever, cough, tachypnoea, expiratory wheeze, cyanosis, intercostal recession

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11
Q

What type of virus is RSV

A

It is an enveloped RNA virus, with only one serotype

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12
Q

What is the epidemiology of RSV?

A

Most important respiratory pathogen in childhood. Transmission is by droplet spread or by contact with fomites. Annual epidemic are in winter.

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13
Q

What are the clinical features of RSV?

A
  • Rhinitis
  • Pharyngitis
  • Bronchiolitis
  • Pneumonia – in the elderly and immunocomprimised
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14
Q

How do you manage a patient with RSV?

A
  • Admit to hospital if sever lower respiratory tract disease.
  • Supportive treatment with O2 therapy
  • Ribavarin by aerosol inhalation
  • Palivizumab – monoclonal RSV Ab for high risk infants
  • NO VACCINE yet
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15
Q

What is the definition of pneumonia?

A

Infection of the lung parenchyma

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16
Q

What are the various classifications of pneumonia?

A
  1. Community vs. hospital acquired
  2. Acute vs. chronic
  3. Lobar and bronchopneumonia vs. interstitial
  4. Typical vs. atypical
17
Q

What is a community acquired pneumonia?

A

Pneumonia presenting in the community or within 48 hrs of attending hospital.

18
Q

Is CAP a big problem?

A

Yes, 6th most common cause of death worldwide, leading cause of infectious death in the USA and UK

19
Q

What are the bacterial causes of CAP?

A
  1. Streptococcus pneumonia
  2. Moraxella catarrhalis
  3. Haemophils influenza
  4. Staphylococcus aureus
  5. “atypicals” - Mycoplasma pneumonia
    - Legionella pneumophilia
    - Chlamydia spp
    - Coxiella burnetti
20
Q

What are the viral causes of CAP?

A

These are less common.

1) RSV is the leading cause of CAP in

21
Q

What are the symptoms of acute “typical” pneumonia?

A
  • Fever
  • Cough
  • Purulent sputum
  • Haemoptysis
  • Chest pain
  • Shallow rapid breathing
  • Reduced chest movements
  • Dullness to percussion
  • Bronchiole breathing/coarse crepitations
22
Q

Streptococcus pneumonia: Describe its morphology, culture characteristics, structure, normal site of acquisition, number of subtypes, and what is causes.

A
  • It is a gram positive diplococcus
  • Grows with alpha haemolysis on blood agar
  • Has a polysaccharide capsule
  • It is part of the normal upper respiratory tract flora, so infections are often autologous
  • There are over 84 different capsular types
  • It is the leading cause of CAP, acute otitis media AOM, acute exacerbations of COPD, and is an important cause of acute bacterial meningitis and septicaemia.
23
Q

What is an “atypical” pneumonia?

A

Atypical pneumonia is when any of the presentation, C-XR, organism, diagnosis and treatment are atypical.

24
Q

What are the causes of an atypical pneumonia?

A 
•	Mycoplasma pneumoniae
•	Legionella pneumophilia serogroups 1 & 6
•	Chlamydia:
       Pneumoniae
       Trachomatis
        Psittaci
•	Coxiella burnetti
•	Pneumocystitis jiroveci (carnii)
•	Respiratory viruses
25
Q

How does Legionalla pneumophilia characteristically present?

A

It is commonly an atypical presentation e.g. fever, confusion, myalgia, non-productive cough, headache
BUT
May have a few of the typical chest signs and patchy consolidation, though this may be in a lobar distribution
Commonly affects middle-aged males
It’s more common in summer months
Requires exposure to contaminated water e.g. showers, air conditioning, sprays

26
Q

How is a legionella infection diagnosed?

A

Antigen/serology

27
Q

How is a legionella infection treated?

A

Macrolides +/- rifampicin

28
Q

Healthcare Acquired Pneumonia: what are the risk factors?

A
  • Extremes of age
  • Chronic pulmonary disease
  • Severity of underlying disease
  • Length of time on ventilator
  • Oropharyngeal (gastric) aspiration e.g. form NG tube
  • Elevated gastric pH (requiring PPI?)
  • Tracheostomy
29
Q

What are the main causative organism of HAP?

A

Staphylococcus aureus – 20%
Pseudomonas aeruginosa, Acinetobacter spp, Escherichia coli, Other coliforms – all account for 60%
Respiratory viruses in the immunocomprimised.

30
Q

How do you asses the severity of pneumonia?

A 
CURB score.
•	Confusion
•	Urea >7mmol/L
•	Respiratory rate >30/min
•	Blood pressure
Systolic 65yrs
NB. Be careful with the young and fit patient, they will probably not have any of these criteria, so an ABG will be needed.
31
Q

How is pneumonia diagnosed?

A

Routine bloods – FBC, U&Es, CRP
Microbiological/virological investigations
CXR

32
Q

What are the microbiological/virology investigations?

A

Specimens:
• Respiratory secretions
• Blood culture
• Urine
• (Serum sample)
Tests:
• Semi-quantitative culture
• Microscopy and culture for mycobacteria
• Urinary antigen test for legionella & streptococcus pneumonia
• Immunofluorescence tests, nucleic acid detection e.g. PCR, or viral culture for viral pathogens

33
Q

What is the treatment for CAP?

A 
Initially empirical, then guided by the results of cultures…
Mild/moderate:
•	Amoxicillin
•	Or clarithromycin
Severe:
•	Cefuroxime + clarithromycin
•	Benzylpenicillin + clarithromycin
•	Clarithromycin + rifampicin for legionnaires
34
Q

What is the treatment for HAP?

A

Empirical, then guided by cultures…
• Broad spectrum Beta-lactam e.g. piperacillin-tazobactam
• Aminoglycosides e.g. gentamicin
• Glycopeptide e.g. vancomycin
• Quinolone e.g. ciprofloxacin

35
Q

Is pneumonia preventable?

A

Yes…

  1. Vaccination (BCG/SP/Influenza)
  2. Penicillin prophylaxis
  3. Stop smoking
  4. Hyperchlorination and heating / good sanitary practices for public places re. air conditioning etc to prevent legionnaires
  5. Handwashing for viral pathogens
  6. Contact tracing and prophylaxis for M. tuberculosis

Respiratory Medicine (9 decks)

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