L21 - Lower Respiratory Tract Infection (1)

Question 1

Wheezing sound explanation

Answer 1

Abnormal breathing sound (high-pitched, whistling sound) due to lower airway obstruction (e.g. asthma, croup)

Question 2

Stridor

Answer 2

Stridor is a high pitched wheezing sound resulting from turbulent air flow in the upper airway. It is primarily inspiratory. It can be indicative of serious airway obstruction from severe conditions such as epiglottitis, a foreign body lodged in the airway, or a laryngeal tumor. Stridor is indicative of a potential medical emergency and should always command attention. (Can be heard without using stethoscope)

Question 3

tracheolaryngobronchitis (definition)

Answer 3

Also known as croup; inflammation in the subglottic area resulting in dyspnoea and inspiratory stridor

Question 4

tracheolaryngobronchitis (epidemiology)

Answer 4

relatively common in children (3 months to 3 years); peak incidence at 2 years of age

Question 5

tracheolaryngobronchitis (pathogen)

Answer 5

Mainly viruses such as parainfluenza virus, influenza virus, respiratory syncytial virus

Mycoplasma pneumoniae

Question 6

tracheolaryngobronchitis presentation

Answer 6

1) Fever
2) laryngitis
3) Insiratory stridor with or without respiratory distress
4) wheezing sound
5) tachypnoea or dyspnoea
6) rales
7) Hypoxaemia

Question 7

tracheolaryngobronchitis diagnosis

Answer 7

Clinical diagnosis. Aetiological diagnosis by viral culture or antigen detection if necessary.

Question 8

Croup treatment

Answer 8

oxygen, nebulized bronchodilators.

Question 9

Pertussis alternate name

Answer 9

whooping cough

Question 10

Pertussis pathogen

Answer 10

Bordetella pertussis, a Gram negative coccobacillus

Question 11

pertussis epidemiology

Answer 11

1) Epidemic in most populations; transmitted via respiratory droplets
2) Not just a disease of childhood. In developed countries, overall disease burden shifting to adolescents and adults. Pertussis is a common but under-recognized cause of chronic cough in adolescents and adults.
3) In many western countries, nosocomial outbreaks of pertussis have been described.

Question 12

Pertussis pathogenesis and 3 phases of disease

Answer 12

1) Filamentous haemagluttinin, helps in attachment to ciliated respiratory epithelium
2) Production of a number of toxins:
- pertussis toxin (PT), adenylate cyclase toxin (ACT), tracheal cytotoxin, dermonecrotic toxin (DNT), pertactin (PTN)
3) Incubation period from less than 1 week to more than 3 weeks
4) 3 phases of disease
a) Catarrhal phase: rhinorrhoea, conjunctival injection, malaise, low grade fever, dry cough
b) Paraoxysmal phase: short expiratory bursts followed by an inspiraory gap (whoop)
c) Convalescent phase

Question 13

Pertussis presentation

Answer 13

a) Catarrhal phase: rhinorrhoea, conjunctival injection, malaise, low grade fever, dry cough
b) Paraoxysmal phase: short expiratory bursts followed by an inspiraory gap (whoop)

Chronic cough in general; symptomatology in adolescents and adults differ from that in children

Question 14

Pertussis complications

Answer 14

pneumonia; haemorrhage; pneumothorax; central nervous
 system abnormalities (convulsion, encephalopathy).

Question 15

Pertussis diagnosis

Answer 15

culture of nasopharyngeal aspirate or swab on special medium (Bordet-Gengou medium).

Serology (not widely available and may not be useful in acute infection).

PCR of nasopharyngeal specimens.

Question 16

Pertussis treatment

Answer 16

Specific antibiotic therapy: macrolides (e.g. erythromycin, clarithromycin, azithromycin).

Question 17

Pertussis vaccination

Answer 17

1) Killed whole-cell vaccine
- protection not life long
- adults have partial or little immunity
- lots of side effects (pain, swelling, high fever)
2) Acellular vaccine (aP)
- A subunit vaccine presents an antigen to the immune system without introducing viral particles. It is the combination of different pathogenic mechanisms (e.g. filamentous haemagglutinin) instead of using whole cell
- fewer side effects
- From 2007, HK childhood immunization programme replaced killed whole-cell vaccine with aP vaccine delivered in combined formula DTaP-IPV. (D=diphtheria toxoid, T=tetanus toxoid, aP= acellular purtussis, IPV=inactivated poliomyelitis vaccine)
- **[IPV replaved oral poliomyelitis vaccine which is live attenuated)

Question 18

Pneumonia Definition

Answer 18

Inflammation affecting the parenchyma of the lung (respiratory bronchioles and alveolar units).

Question 19

Common causes of community-acquired pneumonia

Answer 19

a) Bacteria: Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae;

in some clinical or epidemiological settings, Staphylococcus aureus, Enterobacteriaceae (especially Klebsiella pneumoniae), Legionella pneumophilia, and Burkholderia pseudomallei (melioidosis), and Mycobacterium tuberculosis (tuberculosis) are also important considerations.

b) Viruses: respiratory syncytial virus (especially in infants, children), influenza virus, parainfluenza viruses, coronaviruses, etc.

Question 20

Pneumonia - Route of infection

Answer 20

1 Direct inhalation of infectious particles from ambient air.

2 Aspiration of secretions from the mouth and nasopharynx.

3 Rarely: haematogenous spread from another focus of infection in the body.

Question 21

Approach to Pneumonia

Answer 21

1 History.

a) Clinical setting: acute or chronic; age, underlying illness, occupation, travel history, animal
contacts, etc; community- or hospital-acquired.

b) Patient characteristics - e.g. age, any defect in host resistance (opportunistic pathogens)? Exposure history - Possible exposure to specific pathogens (human, animals, environment)?

2 Physical examination.

3 Investigations.

a) Blood counts, blood gas.
b) Cultures: respiratory tract specimens, blood, pleural fluid.
c) Radiological examinations: plain X ray; CT scan in selected cases.
d) Sputum examination.
i) Macroscopic examination: colour, amount, consistency, (odour); e.g. ‘rusty’ sputum (Streptococcus pneumoniae), ‘currant-jelly’ sputum (Klebsiella pneumoniae). Not sensitive or specific, though.
ii) Gram stain: leukocytes (neutrophils, mononuclear cells), epithelial cells (quality of specimen), predominant flora.
iii) Culture: blood agar, chocolate agar, selective media (e.g. Legionella) when indicated.
e) Viral investigations on respiratory specimens: antigen detection (e.g. by direct immunofluorescent staining, immunochromatographic tests), viral culture, PCR/RT-PCR.
f) Other respiratory tract specimens.

i) More invasive procedure generally have a higher yield for the true
pathogens. However, one needs to balance between risk of procedure
and the anticipated pathogens and yields.

ii) Transtracheal aspiration (seldom performed nowadays).
iii) Endotracheal aspiration.
iv) Fibre optic bronchoscopy + bronchoalveolar lavage (BAL).
v) Transbronchial biopsy, open lung biopsy.
vi) Pleural effusion, pleural biopsy.
vii) Nasopharyngeal aspirate: mainly for respiratory viruses.
g) Serology: mainly for ‘atypical’ pneumonia pathogens (e.g. Mycoplasma, Chlamydia, Chlamydophila, Legionella, viruses). Not always useful in the acute stage.
h) Urine antigen detection assays: Streptococcus pneumoniae, Legionella pneumophila serogroup 1.

Question 22

Therapy of pneumonia: general considerations

Answer 22

1) General supportive measures: oxygen, cardiovascular support, etc.
2) Treat as outpatients or inpatients?
3) Oral or parenteral antibiotics?
4) Empirical therapy or known-pathogen therapy?
5) Empirical therapy: usually a beta lactam antibiotic (e.g. penicillins or cephalosporins) ± a macrolide (e.g. erythromycin, clarithromycin, azithromycin) or a tetracycline.

Different antibiotics have been used for the treatment of pneumonia in different clinical settings. However, antibiotics must be chosen carefully: a balance between clinical efficacy, antibiotic resistance, and cost is essential. Guidelines on the treatment of community-acquired pneumonia may be obtained from various authorities like British Thoracic Society

Question 23

Acute community acquired pneumonia (CAP) presentation

Answer 23

Fever, chills, pleuritic chest pain, cough, mucopurulent sputum. Mortality 6– 24%.

Question 24

Acute CAP Pathogens

Answer 24

1) Streptococcus pneumoniae: commonest; average ~20% -> pneumococcal pneumonia
2) Haemophilus influenzae: average ~7%.
3) Staphylococcus aureus (elderly; post-influenza pneumonia); average ~3%.

Although S. aureus is often quoted as a typical pathogen seen in secondary bacterial pneumonia in patients with influenza, it is not necessarily the commonest one. In most epidemics or pandemics of influenza, Streptococcus pneumoniae is the commoner bacterial pathogen involved.

5) Other bacteria such as Klebsiella pneumoniae.
6) Viruses: especially in children (RSV, parainfluenza), primary influenza pneumonia.

Question 25

Pneumococcal Pneumonia pathogen and epidemiology

Answer 25

Pathogen: Streptococcus pneumoniae (pneumococcus)

Epidemiology: Accounts for 16–60% of acute community-acquired pneumonia.

Question 26

Pneumococcal pneumonia risk and predisposing factor

Answer 26

Risk: Increasing problem of antibiotic resistance.

Predisposing factors: old age, smoking, institutionalization, COAD, chronic liver and renal diseases, congestive heart failure, splenectomy.

Question 27

Pneumococcal pneumonia Vaccines

Answer 27

Pneumococcal vaccines are available for the prevention of invasive pneumococcal diseases and pneumonia.

There are 2 types of pneumococcal vaccine currently available, the polysaccharide vaccine (23-valent) and the conjugate vaccines (7- and 13-valent vaccines are registered in Hong Kong at the moment). Since 2009, the vaccine is made available to at-risk populations in Hong Kong.

Question 28

Atypical pneumonia characteristics

Answer 28

a) Routine culture of sputum does not reveal significant pathogens.
b) Not responding to beta lactam antibiotics commonly used for the treatment of pneumonia.
c) Sometimes may have a more prolonged course of illness.
d) May not appear very ill clinically (“walking pneumonia”)

Question 29

Atypical pneumonia pathogens

Answer 29

a) Bacteria: e.g. Mycoplasma pneumoniae, Chlamydia and Chlamydophila, Legionella pneumophila.
b) Viruses: e.g. influenza virus, adenovirus, parainfluenza virus, respiratory syncytial virus, coronaviruses.

Question 30

Atypical pneumonia epidemiology

Answer 30

Can affect any age group but often more severe in the elderly.

Question 31

Legionella characteristics

Answer 31

Aerobic

Gram negative

non-spore-forming

bacilli

Occurs in natural and artificial fresh water environments.

Question 32

Legionella pneumophila characteristics

Answer 32

a) Aerobic, Gram negative, non-spore-forming bacilli
b) Colonizes artificial water sources, such as cooling towers and other water distribution systems, such as potable water.
c) Aerosolization and aspiration are the commonest routes of transmission.

Question 33

Clinical diseases caused by legionella

Answer 33

a) Pontiac fever: an acute, self-limiting, flu-like illness without pneumonia.
b) Legionnaires’ disease: pneumonia; diarrhoea, nausea, vomiting, abdominal pain, extrapulmonary diseases.

Question 34

Route of transmission of legionella diseases

Answer 34

Aerosolization and aspiration are the commonest routes of transmission.

Ingestion of contaminated water source

Question 35

Legionellosis diagnosis

Answer 35

bacterial culture, urine antigen detection, serology (antibody detection), direct immunofluorescent staining of clinical specimens.

Question 36

Legionellosis treatment

Answer 36

macrolide or fluoroquinolone antibiotics. Beta lactam antibiotics are generally not effective for legionellosis.

Question 37

Nosocomial pneumonia epidemiology

Answer 37

Hospital-acquired pneumonia. Accounts for 10% to 20% of all nosocomial infections.

Question 38

Nosocomial pneumonia risk factors

Answer 38

a Advanced age.

b Underlying diseases.

c Altered mental status.

d Intubation and use of respiratory equipment.

e Use of antacids and H2-antagonists with reduction of gastric acidity.

Question 39

Nosocomial pneumonia pathogens

Answer 39

Often caused by aerobic Gram negative bacilli, e.g. Enterobacteriacae such as Escherichia coli, Klebsiella pneumoniae, or non-fermenters like Pseudomonas aeruginosa, Acinetobacter baumannii; or other multi-resistant bacteria such as meticillin-resistant Staphylococcus aureus.

Question 40

Aspiration pneumonia Pathogenesis

Answer 40

Can occur in any condition in which consciousness is altered and the normal gag and swallowing reflexes are impaired; e.g. alcoholism, cerebrovascular disorders, convulsion.

Three important pathogenic mechanisms:

1) chemical pneumonitis (acute, e.g. due to gastric acid)
2) bronchial obstruction with particulate matter (acute)
3) bacterial aspiration pneumonia (insidious, need incubation period, 2-4 days after aspiration episode)

Question 41

Aspiration pneumonia presentation

Answer 41

1) acute
2) insidious: fever, weight loss, productive cough, putrid sputum

Question 42

Aspiration Pneumonia Pathogens

Answer 42

Predominantly the oral flora: anaerobes (Bacteroides, Porphyromonas, Prevotella, Fusobacterium, anaerobic cocci), Streptococcus (community- acquired); Gram negative bacilli, Staphylococcus aureus (community- acquired or nosocomial).

Question 43

Aspiration pneumonia treatment

Answer 43

Often needs broad spectrum coverage against aerobic and anaerobic organisms.

Question 44

Which lung is more commonly affected by Aspiration Pneumonia

Answer 44

Right lung, because the right bronchi is more vertical

Question 45

Lung abscess predisposing conditions

Answer 45

a Aspiration due to impaired conscious level, e.g. alcoholism, stroke,
general anaesthesia, drug overdose, seizures, etc.

b Poor dental hygiene with periodontal disease, gingivitis.

c Bronchiectasis, bronchial obstruction, cavitating pulmonary infection.

d Septic embolization (e.g. infective endocarditis), bacteraemia.

e Amoebic lung abscess (Entamoeba histolytica; very rare).

Question 46

Lung abscess pathogen

Answer 46

Usually due to mixed oral flora if the predisposing cause is aspiration -

i.e. [anaerobes (Bacteroides, Porphyromonas, Prevotella, Fusobacterium, anaerobic cocci), Streptococcus (community- acquired); Gram negative bacilli, Staphylococcus aureus (community- acquired or nosocomial).]

Question 47

Empyema thoracis definition

Answer 47

Abscess in the pleural cavity.

Question 48

Empyema thoracis causes

Answer 48

a) Complication of pneumonia (50% to 60%).
b) Complication of intrathoracic surgery or trauma: oesophagus, mediastinum, cardiac surgery (25%).
c) Secondary to subdiaphragmatic sepsis.

Question 49

Empyema thoracis pathogens

Answer 49

a) Secondary to pneumonia: Staphylococcus aureus, Streptococcus pneumoniae, etc.
b) Secondary to surgery or perforation of oesophagus: anaerobes; aerobic Gram negative bacilli, Staphylococcus aureus, Actinomyces, etc.

Question 50

empyema thoracis treatment

Answer 50

a) Adequate drainage of collections: percutaneous catheters, chest drains, surgery if necessary.
b) Antibiotics: according to pathogen(s) involved; often requires a prolonged course of antibiotic.
c) Decortication may be necessary in some patients.