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a path 3 > MICRO: Respiratory tract infections > Flashcards

MICRO: Respiratory tract infections Flashcards

1
Q

Covered here:

  • Pneumonia
  • Bronchitis
  • Empyema
  • Aspergillosis/PCP
  • Antibiotic management of CAP/HAP
A
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2
Q

List the types respiratory defence compromise and their effects.

A
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3
Q
  • 18yo female; fever, cough and malaise
  • Diagnosed with flu by GP (no ABx given)
  • Attended A&E with…
    • T: 38C
    • 87% sats on room air
    • Chest clear, RR 24
    • Bloods (WCC 40.8, Neut 36.3, CRP 63)
A

Streptococcus pneumoniae

Investigations diagnosis

  • CXR - double heart border (‘Sail’ sign)
  • CT - densely consolidated and collapsed lower lobe
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4
Q

What are the microbiological characteristics of streptococcus pneumoniae? What is it sensitive to and what is the exception?

A
  • Alpha-haemolytic and optochin-sensitive
  • Gram-positive cocci (chains and pairs)
  • Optochin sensitivity shows that it may be streptococcus pneumoniae
  • Almost always penicillin-sensitive
  • Penicillin-resistance strains may be imported from Southern Europe (so travel history may be important)
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5
Q

What % of CAP is made up by S. pneumoniae?

A

30-50%

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6
Q

How does streptoccus pneumoniae RTI present?

A
  • Acute onset
    • Severe pneumonia
    • Fever and rigors
    • Lobar consolidation
    • Rusty coloured sputum is characteristic of S. pnuemoniae
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7
Q

What is pneumonia and what is the mortality/admission rate?

A

Pneumonia – inflammation of the lung alveoli

Patients are sick with a mortality of 5-10%

20-40% admitted to hospital

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8
Q

What are the clinical features of pneumonia?

A
  • Fever
  • Cough
  • Abnormal CXR
  • Pleuritic chest pain
  • SoB
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9
Q

How is pneumonia classified? What are some risk factors important to consider?

A

Classification:

  • Community-acquired
  • Hospital-acquired/nosocomial (i.e. ventilator-associated)

Underlying factors to consider

  • Pre-existing lung disease
  • Immunocompromise
  • Geography, seasons, epidemics
  • Travel, exposure to animals
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10
Q

Why is no identification of CAP organisms usually made?

A

NO microbiological identification of the pathogen is made in most cases:

  1. Often due to difficulty obtaining a good sputum sample
  2. And because of early treatment with antibiotics
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11
Q

What are the main CAP organisms?

A

TYPICAL (85%)

  • Streptococcus pneumoniae
  • Haemophilus influenzae

ATYPICAL (15%)

  • Legionella
  • Mycoplasma
  • Coxiella burnetii (Q fever) from exposure to farm animals (also causes hepatitis)
  • Chlamydia psittaci (Psittacosis) from exposure to birds (can cause splenomegaly, rash, haemolytic anaemia)

Other organisms:

  • Moraxella catarrhalis
  • Staphylococcus aureus
  • Klebsiella pneumoniae
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12
Q

What is the effect of age on CAP organisms?

A
  • 0-1 months –> E. coli, GBS, Listeria monocytogenes
  • 1-6 months –>Chlamydia trachomatis, Staphylococcus aureus, RSV
  • 6 months - 5 years –> Mycoplasma pneumoniae, Influenza
  • 16-30 years –> Mycoplasma pneumoniae, Streptococcus pneumoniae
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13
Q

What are the signs of pneumonia on examination?

A
  • Pyrexia
  • Tachycardia
  • Tachypnoea
  • Cyanosis
  • Bronchial breathing
  • Crackles
  • Dullness to percussion/tactile vocal fremitus

NB: particularly in young people, you may not find symptoms localising to the chest until they decompensate.

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14
Q

What investigations should be done for pneumonia?

A
  • FBC, U&E, CRP
  • BCs, Sputum MC&S
  • ABGs
  • CXR
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15
Q

What are the components of the CURB-65 score?

A
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16
Q

What is bronchitis and who is usually affected?

A

Bronchitis – inflammation of medium-sized airways

Mainly occurs in smokers

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17
Q

What are the clinical features of bronchitis?

A

Presentation

  • Cough
  • Fever
  • Increased sputum production
  • Increased shortness of breath
  • CXR is usually NORMAL
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18
Q

Which organisms typically cause bronchitis?

A
  • Viruses
  • Streptococcus pneumoniae
  • Haemophilus influenzae
  • Moraxella catarrhalis
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19
Q

How do you treat bronchitis?

A
  • Bronchodilation
  • Physiotherapy
  • Antibiotics
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20
Q

What does this CXR show and what organisms may be responsible?

A

CXR showed a cavitation:

  • Staphylococcus aureus
  • Klebsiella pneumoniae
  • Haemophilus influenzae
  • TB
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21
Q

Which is most likely?

A

All of the above

But Haemophilus influenzae is the most likely

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22
Q

When is H. influenzea infection more common?

A

In pre-existing lung disease

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23
Q

What % of CAP is caused by H. influenzae?

A

15-35% of CAP

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24
Q

What are the microbiological characteristics of H. influenzae?

A

Gram-negative cocco-bacilli (stain on chocolate agar)

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25
Q
A

Legionella pneumophilia

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26
Q

How is Legionella pneumophilia transmitted?

A
  • Spread via inhalation of infected water droplets = e.g. air conditioning, hot water tanks, fountains, car wiper liquid, gyms, saunas

NB: Serious as can cause multi-organ failure

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27
Q

How is Legionella grown?

A

On a buffered charcoal yeast extract

28
Q

What is a cellular feature that defines all atypical pneumonia organisms?

A

Pneumonia caused by organisms without a cell wall:

  • Mycoplasma
  • Legionella
  • Chlamydia
  • Coxiella
29
Q

What must be considered when prescribing antibiotics for atypical pneumonias? Can you prescribe penicillins?

A

Cell-wall active antibiotics (e.g. penicillins) do NOT work

So need agents that work on protein synthesis like:

  • Macrolides (clarithromycin/erythromycin)
  • Tetracyclines (doxycycline)
30
Q

What investigations are done for atypical pneumonias?

A
  • Urinary antigen or legionella and pneumococci
  • Serology for all others
31
Q

Extra-pulmonary features are characteristic of CAP. True or false?

A

False - features such as hepatitis and hyponatraemia are characteristic in atypical pneumonias

32
Q

What are the general clinical features of atypical pneumonias?

A

Extra-pulmonary features like hepatitis and hyponatraemia

Flu-like prodrome before fevr and pneumonia

33
Q

What are the features of legionella pneumophilia? How is it diagnosed? What is the treatment?

A

Associated with:

  • Confusion
  • Abdominal pain
  • Diarrhoea
  • Lymphopaenia
  • Hyponatraemia

Investigation: urinary antigens

Sensitive to macrolides

34
Q

How is Q fever transmitted? How is it diagnosed? What is the treatment?

A

Common in domesticated farm animals and transmitted by aerosol or milk

Investigation: serology

Sensitive to macrolides

35
Q

How is chlamydia psittaci transmitted, diagnosed and treated?

A

Spread from birds by inhalation

Investigation: serology

Sensitive to macrolides

36
Q
  • 74yo woman
  • SOB, fever (38.5C), right-sided pleuritic chest pain, reduced percussion note & decreased air entry right base
  • PMHx IHD, CABG, AF;
  • DHx warfarin
  • Otherwise well
  • Admitted –> commended on cefuroxime and doxycycline –> continued to spike fevers

Whta is the cause? Why did antibiotics not help?

A
  • CXR = homogenous shadowing with meniscus level of right side (CT à empyema with collapsed lung underneath)
  • Diagnosed empyema
    • These are difficult to treat because they (literally bags of pus) have a wall around them and the pus itself is very acidotic which inactivates the antibiotics à hence why she continued to spike fevers even on ABx
37
Q

If a RTI fails to improve on treatment what should you suspect?

A

Failure to improve on treatment, suspect the following:

  • Empyema/abscess
  • Not receiving/absorbing antibiotics
  • Immunosuppression
  • Resistant organisms (travel hx)
  • Proximal obstruction (tumour)
  • Other diagnosis (lung cancer, cryptogenic organising pneumonia
38
Q
  • 21yo male, from Ecuador
  • Cough and WL
    • U&Es normal
    • Hb 10.4
    • WCC 9.8
    • HIV -ve
    • CRP 173
    • Alb 31
  • What is the most likely cause?
A

TB

  • CXR = right-sided apical shadowing, diagnosed TB
39
Q

What are the microbiological features of TB?

A
  • Staining:
    • An auramine stain (left) and a Ziehl-Neelsen stain (right) will be done
    • Red rods are the acid-fast bacilli

NB: if you suspect TB you must tell the lab because MC&S will test for everything but asking for TB culture and smear will lead to decontamination of the sample prior to attempting growth for TB.

40
Q

What is hospital acquired pneumonia?

A
  • A pneumonia onset >48 hours in hospital
  • Patients have often had previous antibiotics and maybe even ventilation
41
Q

What are the most common causes of HAP?

A
  • Enterobacteriaciae (e.g. E. coli, K. pneumoniae) – 31%
  • Staphylococcus aureus – 19%
  • Pseudomonas spp – 17%
  • Haemophilus influenzae – 5%
  • Acinetobacter baumanii – 4%
  • Fungi (Candida spp) – 7%
42
Q

Which investigation is desirable to diagnose HAP?

A

Bronchial lavage (differentiate upper respiratory from lower respiratory flora)

43
Q
  • 64yo retired general
  • Treated for lymph node TB
  • Increasing SOB, non-productive cough, chest exam normal
  • CXR = bilateral ground-glass shadowing (“bat’s wing”)
A
44
Q

What can be seen on this CXR and name a cause?

A

CXR shows bilateral ground-glass shadowing (you can see the pulmonary markings through the opacification) in a “bat wing” formation (i.e. centrally)

May be caused by PCP

45
Q

What type of organism is Pneumocystic jirovecii (PCP)? Where is it found normally?

A

Protozoan

In the environment

46
Q

What are the clinical features of PCP?

A
  • Insidious onset
    • Dry cough
    • Weight loss
    • SOB
    • Malaise
  • NOTE: the walk test (attaching an oxygen saturation probe and asking the patient to walk) will show desaturation on exertion
47
Q

How do you diagnose, treat and prevent PCP?

A

Investigations: bronchoalveolar lavage

Treatment: co-trimoxazole (septrin)

Prophylaxis: co-trimoxazole

48
Q

What are the microbiological features of PCP? (Why is the term PCP technically wrong?)

A

Immunofluorescence assay shows the characteristic cysts which resemble crushed ping-pong balls and are present in aggregates of 2-8 (and not to be confused with Histoplasma or Cryptococcus, which typically do not form aggregates of spores or cells)

PCP may also be detected by Silver stain in cytology labs

Pneumocystic carinii penumonia - only found in rats and terminilogy no longer used.

49
Q
  • 22yo man, chemotherapy for leukaemia
  • Prolonged neutropenia (<1.0), fevers, raised inflammatory markers
  • ABx so far = meropenem, ciprofloxacin, vancomycin, tazocin, ganciclovir
A
  • CT thorax = non-specific (interstitial) changes on the CT scan
  • Aspergillus fumigatus
50
Q

What is shown below?

A

Hyphae of aspergillus on the right

51
Q

What are the 3 types of respiratory phenotypes of aspergillus fumigatus infection?

A
  1. Allergic bronchopulmonary aspergillosis (ABPA)
    • Chronic wheeze
    • Eosinophilia
    • Bronchiectasis
  2. Aspergilloma
    • Fungal ball, often in pre-existing cavity
    • May cause haemoptysis
  3. Invasive aspergillosis
    • Immunocompromised
    • Treatment: amphotericin B
52
Q

What are the clinical features of ABPA?

A
  • Chronic wheeze
  • Eosinophilia
  • Bronchiectasis
53
Q

What are the clinical features of aspergilloma?

A
  • Fungal ball, often in pre-existing cavity
  • May cause haemoptysis
54
Q

What are the clinical features of invasive aspergillosis?

A
  • Immunocompromised
  • Treatment: amphotericin B
55
Q

What RTI can be caused in the following conditions?

  • HIV
  • Neutropenia
  • BM transplant
  • Splenectomy
A
  • HIV
    • PCP, TB, Atypical mycobacteria
  • Neutropoenia
    • Fungi (e.g. Aspergillus spp)
  • Bone Marrow Transplant
    • CMV
  • Splenectomy
    • Encapsulated organisms (S. pneumoniae, H. influenzae, malaria)
56
Q

What general invetigations are used to diagnose LRTI?

A
  • Sputum/induced sputum -take 24-48hrs
  • Blood cultures
  • BAL
  • Pleural fluid
  • Antigen tests
  • Antibody tests
  • Immunofluorescence
  • PCR
57
Q

Which antigen tests are used in the diagnosis of LRTI?

A
  • Limited urine antigen tests available for: Legionella pneumophila + Streptococcus pneumoniae

Send in severe CAP

58
Q

Which RTI are antibody tests useful in diagnosis?

A
  • Only useful on paired serum samples (one acutely unwell and another when getting better). Usually collected on presentation and 10-14 days later + looks for a rise in antibody level over time

Most useful organisms to send antibody tests for because they are difficult to culture:

  • Chlamydia
  • Legionella
59
Q

What RTI can be diagnosed using immunofluorescence?

A
  • Antibody is labelled with fluorescent dye
  • Often used in virology
  • PCP immunofluorescence is the most commonly used one in microbiology labs - PCP may also be detected by Silver stain in cytology labs
60
Q

What is the general antibiotic management of CAP?

A

Antibiotic therapies of RTIs – “I would consult the local guidelines”

CAP: Empirical Therapy (each hospital has its own guidelines)

  • Mild-Moderate:
    • Amoxicillin [OR erythromycin/clarithromycin]
  • Moderate-Severe
    • Needing hospital admission: Co-amoxiclav (augmentin) AND clarithromycin
    • Allergic: Cefuroxime AND clarithromycin
61
Q

What is the general antibiotic management of HAP?

A

HAP: Empirical Therapy (need a lot of gram -ve cover)

  • 1st Line - Ciprofloxacin ± vancomycin
  • 2nd Line/ITU - Piptazobactam AND vancomycin
  • Specific Therapy:
    • MRSA: Vancomycin
    • Pseudomonas: Piptazobactam OR ciprofloxacin ± gentamicin
62
Q
A
63
Q
  • 21yo man, no PMHx, smoker, drinker
  • Presented cough, SOB, sats 89% room air, hypotensive
  • CXR = RUZ pneumonia
  • What other treatment is required?
A
  • Treatment:
    • Cefuroxime and clarithromycin (hypotensive = query allergic)
      • Worried about H. influenzae and covers for atypicals
    • Fluid resuscitation
    • Supplemental O2
    • Senior support requested

Coamox and clarithromycin is more correct because cef and clarithromycin is not used as much

64
Q

Same case:

  • 4 hours later, intubated and ventilated
A
  • Day 2 ITI blood cultures grew streptococcus pneumoniae à cleared up by 2 months after admission
65
Q

How do you prevent pneumonia in the young population and adults?

A
  • Smoking cessation
  • Vaccination:
    • Childhood immunisation schedule
    • Adults à influenza annually, pnemovax every 5 years
66
Q

What common illness is this ?

A

SARS-CoV-2

Bilateral interstitial changes

Focal changes may be seen on CT

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