6 Respiratory Tract Infections: Bacterial Infections

Question 1

Describe how pneumonia is classified

Answer 1

Pneumonia is classified as:

• Community-acquired (CAP)
• Nosocomial (hospital-acquired)

CAP is further divided into:

• Typical
• Atypical

Question 2

Describe community-acquired pneumonia (CAP)

Answer 2

• A leading cause of death
• Majority are caused by bacterial pathogens
• Most often due to Streptococcus pneumoniae

Question 3

Describe how a diagnosis of pneumonia can be made

Answer 3

• The presence of new symptoms or signs of lower respiratory tract infection
  AND
• New pulmonary shadowing on chest X-ray (sensitivity 50% to 85%)

Question 4

Give the pathogenesis of Pneumonia

Answer 4

• Microaspiration of oropharyngeal contents during sleep (most common cause)
• Inhalation of aerosol drops ranging in size from 0.5-1 um (2nd most common cause)
• Bloodstream infection (least common cause)

Question 5

Describe bronchopneumonia

Answer 5

• It begins as acute bronchitis and spreads locally into the lungs
• The lower lobes or right middle lobe are usually involved
• The lung has patchy areas of consolidation
• Microabscesses (pus-filled cystic space) are present in the areas of consolidation

Question 6

Describe lobar pneumonia

Answer 6

• Complete or almost complete consolidation (air replaces with something else) of a lobe of a lung

Question 7

List some complications of pneumonia

Answer 7

• Lung abscess, emphysema (pus in the pleural cavity)

- Sepsis

Question 8

List the causative organisms

Answer 8

• Conventional bacteria cause 60-80% of all cases of CAP
• ‘Atypical’ bacteria cause 10-20% of CAP
• Viruses cause 10-20% of CAP

Question 9

Describe upper respiratory tract infection

Answer 9

The most common cause is rhinovirus (common cold). Other viruses:
- influenza virus, Adenovirus, enterovirus respiratory syncytial virus

Bacteria may cause roughly 15% of sudden onset pharyngitis presentations.
The most common are:
- Streptococcus pyogenes

Question 10

How can one make a diagnosis of the common cold

Answer 10

The presence of classical features for rhinovirus infection,

coupled with the absence of signs of a bacterial infection or serious respiratory illness, is sufficient to make the diagnosis of the common cold

The common cold is a clinical diagnosis
(diagnostic testing is not necessary)

Question 11

Describe how influenza can be tested for:

Answer 11

• Nasal aspirates
• Swabs
  best specimens to obtain when testing infants and young children

For adults and older children, swabs + aspirates from the nasopharynx are preferred

Rapid strep swabs can be used to rule out bacterial pharyngitis,
-which could help decrease the number of antibiotics being prescribed for these infections

Question 12

Give the clinical findings in Lower Respiratory Tract Infection

Answer 12

• High fever with productive cough
• Chest pain
• Tachycardia
• Signs of consolidation (alveolar exudate - higher protein content that transudate)

Question 13

Describe streptococcus pneumoniae

Answer 13

(gram-positive diplococcus)

• S. pneumoniae is the most common cause of community-acquired pneumonia (CAP)
• The capsular polysaccharide is the major virulence factor (protection against phagocytosis and drying)
• Relative resistance to penicillin
• Rapid onset, productive cough, signs of consolidation
• Urine antigen testing test excellent screen

Question 14

Describe Haemophilus influenza

Answer 14

Haemophilus influenzae

• gram-negative rod
• Most common bacterial cause of acute exacerbations of COPD
• Most virulent strains have a capsule

H. influenza is a primary cause of CAP in children who have not received Hib (vaccine)

COPD

Question 15

Describe Pseudomonas aeruginosa

Answer 15

• it is a gram-negative rod
• has a capsule
• green sputum (pyocyanin)
• Water-loving bacteria - often transmitted by ventilators
  (hospital-acquired pneumonia - HAP)
  (ventilator-acquired pneumonia - VAP)

The most common cause of nosocomial pneumonia and death due to pneumonia in cystic fibrosis

Hospital-acquired pneumonia

Question 16

Describe Klebsiella penumoniae

Answer 16

• capsule
• common gram -ve organism causing lobar pneumonia in elderly patients in nursing homes
• Common cause of pneumonia in alcoholics

Typical pneumonia associated with blood-tinged, thick, mucoid sputum
- Lobar consolidation and abscess formation is common

Lobar pneumonia

Question 17

List important bacterial causes of upper respiratory tract infections

Answer 17

Atypical causes:

• Interstitial pneumonia, no signs of consolidation
• Insidious onset, low-grade fever
• Non-productive cough
• Both upper + LRT symptoms
• Flu-like symptoms

Question 18

Describe mycoplasma pneumoniae

Answer 18

(no cell wall)

• Most common cause of atypical pneumonia (up to 20% of CAP)
• Common in adolescents + military (closed spaces)
• Risk factor for Guillain-Barre syndrome
• Insidious onset - with low-grade fever

Atypical pneumonia

Question 19

Give some complications of mycoplasma pneumoniae infections (atypical pneumonia)

Answer 19

• Bullous myringitis (painful blisters on the eardrum)

- Cold autoimmune hemolytic anemia - due to anti-IgM (type 2 HSR)

Question 20

Give the treatment of mycoplasma pneumoniae infections (atypical pneumonia)

Answer 20

• No wall targeting abx
  > (resistant to penicillin + cephalosporins)

Give ribosomal abx
e.g. macrolides - erythromycin, azithromycin

Question 21

Describe legionella pneumophila

Answer 21

It is a gram -ve rod (poorly staining)

• Antigens can also be detected in urine
• Water-loving bacterium (water cooler; mists in the produce of grocery stores, outdoor restaurants in summer, rain forests in zoos)
• More common in alcoholics, smokers, and immunocompromised patients

Atypical pneumonia associated with:

• High fever
• Dry cough
• Flu-like symptoms

Question 22

Describe nosocomial pneumonia

Answer 22

Pneumonia contracted by a patient in hospital (HAP) - after 48hrs post-admission

• Ventilators (VAP) and intubation
• Opportunistic infection in patients with severe underlying disease
• Antibiotic therapy
• Immunosuppression

Question 23

List some organisms that can cause nosocomial pneumonia

Answer 23

• Pseudomonas aeruginosa
• E. coli

Gram +ve like S. aureus

Question 24

Describe the management of pneumonia (CAP)

Answer 24

Most managed in general practice, refer if:
- Symptoms + signs suggest a more serious illness/condition (e.g.
cardiorespiratory failure or sepsis)
OR
- Symptoms are not improving as expected with antibiotics

Other things to consider:

• Bacterial resistance to oral antibiotics
• Consider referring young people with CAP to hospital, or seek specialist paediatric advice on further investigation and management

Question 25

Describe how one would confirm a diagnosis of CAP

and how to find the aetiological (causative) agent

Answer 25

• Chest X-ray, culture + stain (moderate + severe)
• Assess severity of disease
• Correction of respiratory failure (ventilator)
• Correction of haemodynamic compromise (fluids)

Targeted therapy

Question 26

Describe how to assess the severity of CAP

state the different criteria needed to be assessed

Answer 26

Criteria; if each point is positive, give a score of one:
- Confusion - mini-mental test score (8 or less) or confusion to time/place
- Urea > 7mmol/L
- Respiratory rate > 30 per min
- Blood pressure:
 > systolic BP < 90mmHg OR
 > diastolic BP < 60mmHg
- 65 years old or older

Question 27

What is the management for a patient with a CAP severity score of 3 or more

Answer 27

(mortality of 15-40%)
- PaO2 < 8 ot SaO2 <92% - arrange urgent admission to hospital

• Co-amoxiclav - 1.2g IV every 8 hours PLUS
• Clarithromycin 500mg IV or PO every 12 hours

Question 28

What is the management for a patient with a CAP severity score of 1 or 2

Answer 28

(mortality 9%)
- Hospital assessment should be considered (especially for a score of 2)
- Prescribe oral amoxicillin 500mg 3x day for 5 days
AND
- If atypical pathogens suspected - clarithromycin 500mg 2x day for 5 days

Question 29

What is the management for a patient with a CAP severity score of 0

Answer 29

(mortality <3%)

• Treatment at home should be considered, depending on clinical judgment and the person’s circumstances
• 1st choice abx - amoxicillin 500mg 3x day for 5 days

!!Important!!
- Check for penicillin allergy (if so - give doxycycline)

Question 30

List some microbiological investigations (for moderate or severe CAP)

Answer 30

• Take blood and sputum cultures
  > consider pneumococcal and legionella urinary antigen tests
• Investigations for legionella if suspected:
  (sputum for culture and immunofluorescence)
• PCR/immunofluorescence for atypical organisms and viruses
  > pleural fluid if available for microscopy, culture, and antigen detection

Question 31

State what bacteria causes cystic fibrosis

Answer 31

Staphylococcus aureus

Question 32

Describe staphylococcus caused cystic fibrosis

Answer 32

• Gram +ve cocci in clumps
• Yellow sputum
• Commonly superimposed on influenza pneumonia and measles pneumonia

Major lung pathogen in cystic fibrosis and IV drug abusers

• Hemorrhagic pulmonary edema
• Abscess formation
• Pneumatoceles (thin-walled air-filled cysts that develop in the lung parenchyma, usually after pneumonia)