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Respiratory Block: Microbiology > Lower Respiratory Tract Infections > Flashcards

Lower Respiratory Tract Infections Flashcards

1
Q

What is the definition of pneumonia?

A

Infection of lung parenchyma (alveoli) most commonly due to a bacterial cause, associated with clinical and / or radiological evidence of consolidation

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2
Q

What is the pathophysiology of pneumonia?

A

Pathogens must reach the alveoli.

  • host defenses overwhelmed by pathogen virulence or inoculum
  • alveolar macrophages produce cytokines to recruit neutrophils
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3
Q

What is the initial step in pneumonia infection?

A

Colonization of upper airways is initial step in infection

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4
Q

What factors predispose to the development of pneumonia?

A
  • alterations in levels of consciousness can compromise epiglottic closure and result in aspiration of oropharyngeal of microbiota
  • pathogens can interfere with normal ciliary function
  • the defenses of the lung when working normally maintain low microbial concentrations in the lower airways
  • HIV compromises many of the components of the pulmonary defenses
  • pulmonary oedema or malnutrition can also impair host defenses
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5
Q

What is community acquired pneumonia?

A

Acute infection of the lower respiratory tract acquired in the community

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6
Q

In general, what are the causes of community acquired pneumonia?

A

Many possible causes, but only a few pathogens account for most of the cases
- Mixed bacterial and viral infections COMMON (especially in paeds)

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7
Q

What are the common bacterial causes of community acquired pneumonia?

A
  1. Streptococcus Pneumoniae
  2. Haemophilus Influenzae
  3. Staphylococcus Aureus
  4. Atypical gram-negative bacilli (e.g. Klebsiella pneumoniae)
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8
Q

What are some of the atypical pathogens that cause community acquired pneumonia?

A
  1. Mycoplasma pneumoniae
  2. Chlamydophilia pneumoniae
  3. Legionella species
  4. Bordetella pertussis
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9
Q

What is the most common viral pneumonia in adults?

A

Influenza A or B (very common in kids too)

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10
Q

What are the common viral causes of community acquired pneumonia?

A
  1. Respiratory Syncytial Virus (RSV)
  2. Influenzae A or B
  3. Human Metapneumovirus
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11
Q

What are the two main opportunistic pathogens that cause community acquired pneumonia?

A
  1. Pneumocystis Jirovecii (PJP)

2. Cytomegalovirus (CMV)

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12
Q

What is the most common bacterial cause of community acquired pneumonia?

A

S. Pneumoniae

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13
Q

What is the most common cause of viral community acquired pneumonia in children?

A

RSV

especially in <3 year olds

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14
Q

What is the most common viral cause of community acquired pneumonia in adults?

A

Influenza Virus

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15
Q

How common are atypical pathogens as a cause of community acquired pneumonia?

A

Relatively uncommon in SA

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16
Q

Where is PJP commonly seen as a cause of community acquired pneumonia?

A

In HIV-infected patients with a CD4 count <200

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17
Q

What is important when considering causes of community acquired pneumonia in the HIV positive population?

A

In HIV the causes of community acquired pneumonia are the same…
BUT
Must consider opportunistic infections
AND
NB to look for TB! Infection with mycobacterium tuberculosis may present as an acute infection

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18
Q

S. Pneumoniae: what is the classification?

A

Gram-positive diplococci, alpha-haemolysis

- mucoid, draughtsman colonies - flat in the middle

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19
Q

S. Pneumoniae: how is immunological protection mediated?

A

Immunological protection is mediated through antibodies directed against capsular polysaccharides

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20
Q

S. Pneumoniae: What has been the effect of the vaccine?

A

Conjugate pneumococcal vaccine implemented in the SA EPI: the vaccine protects against 14 of the >92 serotypes.

  • since the introduction of the vaccine there has been a significant decline in the 14 serotypes of the vaccine
  • but this has created a niche for the other serotypes to grow, the others are therefore increasing
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21
Q

S. Pneumoniae: What does the vaccine protect against?

A

Effective in preventing pneumococcal pneumonia, invasive pneumococcal disease and otitis media
+ Herd immunity

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22
Q

Atypical Pneumonia presentation

A

Atypical pneumonia is slower in onset and milder and not associated with lobar consolidation versus lobar pneumonia

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23
Q

What is the peak incidence of Mycoplasma Pneumoniae?

A

5-15 year olds

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24
Q

What clinical sign is commonly seen with Mycoplasma Pneumoniae?

A

Skin manifestations are common

25
Q

Who is at risk for Legionnaires Pneumophilia?

A

Elderly, males, smokers, and immunocompromised patients are at most risk
= can cause severe disease

26
Q

How is Legionnaires Pneumophilia transmitted?

A

Legionnaires disease is acquired by inhaling water aerosols containing the pathogen

27
Q

Clinical presentation of Chlamydophilia Pneumoniae

A

Clinically indistinguishable from Mycoplasma Pneumoniae infection

28
Q

What are the symptoms of community acquired pneumonia?

A
  • cough
  • sputum production
  • dyspnoea
  • chest pain (pleuritic, hurts to cough)
  • fever
  • fatigue
29
Q

What are the signs of community acquired pneumonia?

A
  • tachycardia
  • tachypnoea
  • pyrexia
  • decreased breath sounds
  • crackles
30
Q

What is important to determine when assessing community acquired pneumonia?

A

The severity of illness

31
Q

Why is the severity of community acquired pneumonia important?

A

It determines:

  • the appropriate site of care
  • extent of microbiological work-up
  • choice of initial empiric antibiotic therapy
32
Q

What score is used to determine severity of community acquired pneumonia in adults?

A

CURB-65 score

33
Q

What are the components of the CURB-65 score?

A

C: Confusion
U: Urea >7mmol/L
R: Respiratory Rate >/= 30 breaths / min
B: Blood Pressure Sys <90mmHg or Dia <60mmHg
65: Age >/= 65 years
*Each feature present gets 1 score

34
Q

What dose a CURB-65 score of 0 mean?

A

Severity: LOW

Where to treat: HOME

35
Q

What dose a CURB-65 score of 1 mean?

A

Severity: LOW

Where to treat: HOME

36
Q

What dose a CURB-65 score of 2 mean?

A

Severity: MODERATE

Where to treat: HOSPITAL

37
Q

What dose a CURB-65 score of 3-5 mean?

A

Severity: HIGH

Where to treat: HOSPITAL: ASSESS FOR ICU ADMISSION

38
Q

What is important to remember when using the CURB-65 score?

A

Pneumonia severity scores such as the CURB-65 score must be used in conjunction with clinical judgement when assessing the severity of a pneumonia case

39
Q

Diagnosis of CAP is based on what 2 factors first?

A
  1. Clinical features

2. Chest X-ray (usually not done for out-patients)

40
Q

What is significant about using a CXR in the diagnosis of CAP?

A

Chest X-Ray: Radiographic features not characteristic enough to suggest most likely microbial cause:

  • helps confirm diagnosis
  • extent of consolidation
  • underlying disorders
  • complications (e.g. pleural effusion)
41
Q

What should be done for all patients with a CURB-65 score >/=2?

A
  1. Sputum for MC&S

2. Blood cultures

42
Q

In general, when are diagnostic investigations indicated in determining the cause of pneumonia?

A

Only in patients requiring hospitalization.

  • most empiric antibiotic regimens are successful in therapy of CAP, especially in mild-moderate cases
  • yield from diagnostic testing for causative microbes is not high
43
Q

What are possible benefits of diagnostic investigations in determining the cause of pneumonia?

A

Allow de-escalation to narrower spectrum antibiotics, may ID unusual pathogen that would not be covered by empiric choice
& useful data for monitoring epidemiology

44
Q

Approach to CAP diagnosis: for patients with severe CAP what should be considered?

A
  • legionella urinary antigen test

- during influenza season nasopharyngeal sample for influenza PCR

45
Q

For CAP, which diagnostic tests are not routinely recommended?

A

1 . Molecular tests to detect other respiratory pathogens

2. Serology for atypical pathogens

46
Q

In which CAP patients is investigation for TB (GeneXpert) recommended?

A
  • HIV positive
  • DM
  • admitted to ICU
  • with subacute illness
  • not responding to empiric antibiotic therapy
47
Q

How is the diagnosis of PJP made?

A

WHO clinical case definition must be used to clinically diagnose P. jirovecii pneumonia
(induced sputum, immunofluorescence staining, PCR)

48
Q

What is the WHO case definition for PCP in patients with HIV?

A
  • dyspnoea on exertion or non-productive cough of recent onset (within the past three months), tachypnoea, fever
  • and CXR evidence of diffuse bilateral interstitial infiltrates
  • and no evidence of bacterial pneumonia: crackles on auscultation with or without reduced breath sounds
49
Q

Paeds guidelines: what is the age cut-off for admission?

A

All children under 2 months with pneumonia must be admitted to hospital.

50
Q

Paeds guidelines: which children >2 months of age should be admitted?

A

Children older than 2 months with:

  • impaired level of consciousness
  • inability to eat or drink
  • cyanosis
  • stridor in a calm child
  • grunting
  • severe chest wall indrawing
  • room air SaO2 <92% at sea level or <90% at higher altitude
  • severe malnutrition
  • family unable to provide appropriate care
  • failure to respond to ambulatory care or clinical deterioration on treatment
51
Q

What is empiric antibiotic therapy based on?

A

Based on commonly encountered pathogens (and their usual susceptibility patterns) in practice environment

52
Q

What other factors should be considered in giving empiric antibiotic treatment?

A
  • age
  • antibiotic use in previous 90 days
  • comorbidities
53
Q

When should antibiotics be administered?

A

Antibiotics should be administered early

- delayed therapy negatively impacts on patient outcomes

54
Q

What is considered definitive therapy in the treatment of CAP?

A

When microbiological investigations detect a causative pathogen, antibiotics should be changed to the narrowest spectrum agent that effectively covers the organism.

55
Q

What is duration of therapy based on?

A

Duration of antibiotic therapy is based on clinical response and causative agent.

56
Q

When should the patient be changed from IV to oral therapy?

A

Once the patient has responded, is stable, able to eat

- take out drip and change to oral therapy

57
Q

What 2 adjunctive therapies are used in severe CAP patients (requiring ICU admission)?

A
  1. Systemic corticosteroids

2. Addition of a macrolide

58
Q

Why are systemic corticosteroids used as an adjunct therapy?

A
  • reduction in need for mechanical ventilation

- reduced mortality

59
Q

Why are macrolides used as an adjunct therapy?

A

Associated with better outcomes if macrolide is added to beta-lactam:

  1. Antimicrobial activity of macrolide (cover atypicals)
  2. Anti-inflammatory / immunomodulatory effects

Respiratory Block: Microbiology (7 decks)

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