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Microbiology > Lower Respiratory Tract Infections > Flashcards

Lower Respiratory Tract Infections Flashcards

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1
Q

Definition of LRTI

A
  • Any infection of the respiratory tract from the vocal cords downwards - includes:
    • Bronchi
    • Bronchioles
    • Alveoli
    • Parenchyma
    • Pleura
    • Pleural cavities
  • Normally bacteriologically sterile
    • Inhaled particles including microorganisms are trapped by mucus and moved to the upper respiratory tract by epithelial cilia (mucociliary escalator)
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2
Q

Pathogenesis of LRTIs

A
  • Paralysis of cilia
  • Excessive volume and/or viscosity of mucus - e.g. CF
  • LOC, paralysis, ventilation ==> failure to protect LRT
  • Failure to cough/loss of swallowing reflex
  • “Colonisers” of LRT are often from URT such as:
    • Haemophilus influenzae
    • Streptococcus pneumoniae
  • Antibiotic therapy will affect URT colonisation
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3
Q

Acute Bronchitis

A
  • Symptoms
    • Cough
    • Trouble sleeping
    • Dyspnoea
    • Nasal congestion
    • Rhinorrhea
    • Sore throat
    • Fever (uncommon)
  • Causes
    • Mostly viral:
      • Influenza
      • RSV
      • Rhinovirus
      • Adenovirus
      • Parainfluenza virus
    • Pertussis - !
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4
Q

Chronic Bronchitis

A
  • Chronic bronchitis - clinical definition:
    • Productive cough for more than 3 months per year for the past 2 years
    • Wheezing
    • Dyspnoea (SOB)
  • Most chronic bronchitis patients develop COPD over time = chronic bronchitis + airflow limitation
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5
Q

Chronic Bronchitis - Infective Exacerbations

A
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6
Q

Pneumonia - Clinical Features

A
  • General:
    • Fever/rigors/sweats
    • Headache
    • Confusion (especially elderly patients)
    • Vomiting/diarrhoea
  • Localised:
    • Breathlessness
    • Cough (may be productive)
    • Haemoptysis
    • Pleuritic chest pains
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7
Q

Pneumonia - Investigations

A
  • General
    • Sats
    • ABGs
    • FBC
    • U&Es
    • CRP - useful for monitoring progress of therapy
    • CXR
  • Microbiological
    • Serum - stored acutely 2-3 weeks later used retrospectively to diagnose
    • Blood cultures - only positive in 15% of severe cases
    • Sputum - shown to be of no clinical value except in cases of TB or Legionella
    • Bronchio-alveolar lavage - optimal sample but only used in severe cases as invasive
    • Urine - test for antigen to Legionella/S.pneumoniae
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8
Q

Pneumonia - Aspiration Pneumonia

A
  • Inhalation of material; about 10% of community cases
  • Usually neurological problem predisposing
  • Commonly affects posterior segment of right upper lobe
  • Can lead to abscess formation
  • May be associated with chemical pneumonitis - inflammation of the lung caused by inhaling irritants
  • Protection of airway important in prevention
  • Treat with antibiotics to cover URT flora e.g. penicillin or cephalosporin plus metronidazole
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9
Q

Pneumonia - Acute Community Acquired

A
  • Common
  • If present less than 48 hours into a hospital admission - community acquires
  • Most commonly due to:
    • Streptococcus pneumoniae
    • Haemophilus influenzae
  • Specific causative organisms:
    • Staphlococcus aureus in flu epidemics
    • Kleibsiella pneumoniae in diabetics and alcoholics = severe
    • *M.catarrhalis *in COPD
  • Sometime viral in children
  • Always consider TB
  • Narrow spectum therapy
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10
Q

Pneumonia - Chronic Community Acquired

A
  • Uncommon
  • Illness progresses over weeks to months
  • TB is the most important cause
  • Wide differential including vasculitides
  • Specialist assessment needed
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11
Q

Community Acquired Pneumonia - Epidemiology

A
  • More common in winter
  • Male 2:1 female
  • More common in elderly
  • 750,000 cases a year in UK
    • 150,000 consult GP
      • 50,000 hospitalised
  • 10% mortality among hospitalised patients
  • Up to 50% mortality if severe
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12
Q

Assessing Severity of CAP

A
  • CURB-65 score
    • Confusion - AMT of 8 or less
    • Urea raised > 7mmol/l
    • Respiratory rate >30/min
    • Blood pressure: systolic <90mmHg +/- diastolic <60mmHg
    • 65 and over
      • >/= 3 - admit to hospital (mortality 22%)
      • 1 or 2 - hospital referral and assessment
      • 0 - treat in community
  • Additional adverse features:
    • Hypoxaemia: PaO2 <8kPa, SaO2 <92%
    • Bilateral or multilobar involvement on CXR
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13
Q

Typical vs Atypical Pneumonia

A
  • Two groups of pathognes
    • Respond to different antibiotics
    • Clinical spectrums differ
    • Cannot tell clinical difference in individual case
  • Typical:
    • Often lobar
    • Caused by: Streptococcus pneumoniae
    • Amoxicillin sensitive
    • Sometimes macrolide sensitive
  • Atypical:
    • Often multisystem, multilobar
    • Causative organisms: Mycoplasma, Chlamydia, Coxiella, Legionella
    • Amoxycillin resistant
    • Macrolide sensitive
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14
Q

Streptococcus Pneumoniae

A
  • Microbiology:
    • Gram positive diplococci
    • Alpha (incomplete) haemolysis
    • Draughtsmen colonies
  • Colonises the nose
  • Transmitted person-person
  • Can invade, causing:
    • Pneumonia
    • Meningitis
    • Endocarditis
    • Bacteraemia (may be only manifestation in toddlers)
  • Sensitive to: amoxycillin and doxycycline, levofloxacin/moxifloxacin
  • Penicillin resistance increasing, although rare in UK
  • Significant cause of mortality amongst susceptible individuals e.g elderly, renal failure, splenectomy
  • Vaccine available against 23 serogroups plus new heptavalent conjugate vaccine
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15
Q

Haemophilus Influenzae

A
  • Several serovars resident in the nose
  • Transmitted person-person
  • Vaccine preventable
  • Capsular strain (a-f)
    • Associated with invasive infection including, meningitis, epiglottitis (HiB vaccine effective)
  • Non-capsular strains
    • Associated with mucosal infections including, otitis media, sinusitis and exacerbations of COPD (HiB vaccine ineffective)
  • Can invade, causing
    • Pneumonia
    • Meningitis
    • Bacteraemia
    • Epiglottitis
    • Septic arthritis
  • ​
    Requires haem (X) and NAD (V) for growth
  • Sensitive to amoxicillin
    • 20% are b-lactamase positive
      • These are sensitive to cefuroxime and co-amoxiclav
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16
Q

Mycoplasma Pneumoniae

A
  • Occurs in epidemics every 3-4 years
  • Cause of primary atypical pneumonia
  • Human to human transmission
  • Most common in children and young adults
  • Rare complications include myringitis and encephalitis
  • Diagnosis is by serology
  • Microbiology:
    • Lacks classical peptidoglycan cell wall
    • Resistant to beta-lactam antibiotics
    • Sensitive to macrolides, tetracyclines and quinolones
17
Q

Legionella Pneumonphila

A
  • Can survive and multiply inside macrophages
  • Can cause:
    • Mild influenza-like URTI = Pontiac fever
    • Severe pneumonia with multi-organ failure = Legionnaire’s disease
      • >50% of cases associated with travel
      • Breeds in stagnant water then spread by cooling tower
18
Q

Chlamydia Pneumoniae and Chlamydia Psittacii

A
  • Obligate intracellular parasites
  • Sensitive to macrolides, tetracyclines and quinolones
  • C.pneumoniae usually self-limiting and mild
    • Human to human transmission
  • C.psittacii can cause severe pneumonia
    • Zoonotic infection from birds
    • Occupational disease of poultry processing industry
19
Q

Coxiella Burnetii

A
  • Causes Q fever
  • Spread can be airborne, through infected milk, faeces and urine of farm animals
  • Can cause severe pneumonia
  • Diagnosis is by serology (Phase 1 and 2 antibodies)
  • Can lead to chronic disease and endocarditis
  • Best treated with tetracyclines
20
Q

Community Acquired Pneumonia - Empirical Treatment

A
  • At home
    • Oral
      • Amoxicillin 500mg tds
        • Alternatively erythromycin 500mg qds or clarithromycin 500mg bd
  • In hospital:
    • Oral
      • Amoxicillin 500mg tds plus erythromycin 500mg qds or clarithromycin 500mg bd
        • Alternatively *levofloxacin *500mg od
    • IV
      • Ampicillin 500mg qds or benzypenicillin 1.2g qds plus erythromycin 500mg qds or clarithromycin 500mg bd
21
Q

MRSA - Hospital Acquired

A
  • Who?
    • Elderly
    • Debilitated
    • Critically/chronically ill
  • What?
    • Bacteraemia
    • UTI
    • Skin and soft tissue infection
  • How?
    • Nosocomial
  • Risk factors?
    • History of MRSA infection
    • Recent surgery
    • Admission to a hospital or nursing facility
    • Anitbiotic use
    • Dialysis
    • Permenant indwelling catheter
  • Antibiotics
    • Multi-drug resistant
  • SSCmec (mobile gene element encoding methicillin resistance)
    • I
    • II
    • III
  • PVL toxin:
    • Rare
22
Q

MRSA - Community Acquired

A
  • Who?
    • Young healthy people: high school, college and professional athletes
  • What?
    • Skin and soft tissue infections
    • Pneumonia
  • How?
    • May spread in families and sports teams
  • Risk factors?
    • Recent antibiotic therapy
    • Minor skin trauma
    • Unusual grooming habits
  • Antibiotics:
    • Resistant only to Beta-lactam antibiotics
  • SSCmec (mobile gene element encoding methicillin resistance)
    • IV
  • PVL toxin
    • Common
23
Q

PVL S.aureus Pneumonia

A
  • Panton-Valentine Leukocidin (PVL) is a cytotoxin produced by some strains of S.aureus that can destroy white blood cells and cause extensive tissue necrosis and severe infection
  • Consider PVL S.aurus pneumonia if:
    • Previously fit and well
    • ‘Flu-like’ illnesss
    • Multi-lobar involvement on CXR +/- effusions and cavitation
    • Haemoptysis
    • Hypotension
    • Leucopaenia
    • High CRP
    • Sputum microscopy showing sheets of staphlococcal-like Gram positive cocci
24
Q

Hospital Acquired Pneumonia

A
  • 3rd most common nosocomial infection
  • Occurs 0.5-1/100 hospital admissions
  • Cause of considerable morbidity/mortality
  • Defined as occurring >48 h after admission
  • Diagnosed by culture, antigen detection or serology
  • Treatment depends on organism involved - if unknown need to cover both S. aureus and P. aeruginosa the two most common causative organisms
    • Early onset infection (<5 days following hospital admission) - *co-amoxiclav *or cefuroxime
      • If recently on antibiotics or other risk factors then - 3rd generation cephalosporin (*cefotaxime *or ceftriaxone) or a fluoroquinolone or piperacillin/tazobactam
25
Q

Pneumonia - Immunocompromised

A
  • Different groups vary in susceptibility to microorgaisms: neutropaenia, HIV, organ transplantation, steroid treatment
  • Lack of neutrophils predisposes to:
    • Gram negatives eg:
      • Pseudomonas
      • Coliforms
    • Gram positives eg:
      • Staphylococcus aureus
      • Viridans streptococci
  • Lack of appropriate T-cells predisposes to:
    • Intracellular pathogens eg. Mycobacterium species
    • Viruses eg. CMV and adenovirus
    • Fungi eg. Cryptococcus neoformans and Aspergillus species
26
Q

Pneumonia - Immunocompromised - Diagnosis and Treatment

A
  • Can be very difficult
  • Strenuous attempts should be made to help identify offending pathogen e.g use of CT scan, bronchoscopy, BAL, needle biopsy
  • Treatment may have to cover a wide range of pathogens
  • Recovery of neutrophil function/T-cell defect will improve prognosis
  • Prophylaxis required in selected patients
27
Q

Pneumonia - Pneumocystis Jiroveci (Carinii)

A
  • HIV related illness
  • Occurs with CD4
  • Fungus: Pneumocystis
  • Pneumonia, onset over several days ==> weeks
  • Important cause of death in AIDS
28
Q

Pneumonia - Pneumocystis Jiroveci (Carinii) - Diagnosis and Treatment

A
  • Diagnosis requires induced sputa or BAL sample
    • Analysed by cytology
    • Pneumocystis can’t be cultured
  • Rx:
    • Refractory to normal antibiotics
    • Responds to co-trimoxazole (Septrin) + steroids
    • Prophylaxis given if CD4< 200
29
Q

Bronchiectasis and Cystic Fibrosis

A
  • Bronchiectasis is due to abnormal structure of bronchi leading to inflammation and obstruction
  • Cystic fibrosis leads to abnormal and tenacious mucus in bronchial tree
  • Both results in cycles of colonization/ infection/ tissue damage
    • Colonising organisms:
      • Staphylococcus aureus
      • Haemophilus influenzae
      • Moraxella catarrhalis
      • Pseudomonas aeruginosa
  • ​​Follow-up involves:
    • Montioring clinically
    • Further X-rays to:
      • Confirm diagnosis
      • Exclude complications
30
Q

Lower Respiratory Tract Infections - Complications - Lung Abscess

A
  • May be due to aspiration, pneumonia, haematogenous spread or malignancy
    • Aspiration usually polymicrobial
    • Haemotogenous abscess usually due to Staphylococcus aureus
    • Rarer causes include:
      • Klebsiella pneumoniae
      • Pseudomonas aeruginosa
      • Fungi
31
Q

Lower Respiratory Tract Infections - Complications - Pleural Effusion

A
  • Pleural effusions complication of chronic bronchiecatasis or CF
    • Diagnosis made by diagnosic tap to determine types:
      • Parapneumonic effusion:
        • Reactive - non-infective
        • pH>7.2
        • Manage conservatively
      • Empyema
        • Infected
        • pH
        • Needs drainage +/- surgery

Microbiology (9 decks)

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