Respiratory Tract Infections Flashcards
1
Q
What are the sterile areas of the respiratory tract?
A
- Sinuses
- Middle ear
- Lower respiratory tract (below larynx)
2
Q
What are the frequent aetiological agents and aetiological therapy in the following URTI conditions:
- Common cold
- Pharyngitis/tonsilitis (with nasal involvement)
- Pharyngitis/tonsilitis (without nasal involvement)
- Sinusitis
- Epiglottis
- Otitis media
- Epiglottitis
- Croup (LTB)
A
- Common cold:
- Rhinovirus
- Parainfluenza virus
- RSV
- Enterovirus
- Coronavirus - Pharyngitis/tonsilitis (with nasal involvement):
- more likely to be viral
- Adenovirus
- Enterovirus
- Reovirus
- Influenza - Pharyngitis/tonsilitis (without nasal involvement):
- Adenovirus
- Enterovirus
- Reovirus
- Influenza
- Group A strep
- Group C and G strep
- Only antimicrobials if bacterial - Sinusitis:
- Viral (common cold syndrome)
- Secondary: H. influenzae, Strep pneumoniae
- Only antimicrobials if bacterial and severe - Epiglottis:
- H. influenzae b
- Always conduct diagnosis of aetiological agent 5
- Needs antimicrobial - Otitis media:
- Pneumococci
- H. influenzae
- Moraxella
- Viruses (flu, RSV) - Croup (LTB):
- Parainfluenza virus
- Influenza A
- RSV
- Inhaled GCs if severe
3
Q
What are the frequent aetiological agents for the following LRTIs?
A
- Acute bronchitis:
- Usually part of viral URTI - Acute exacerbation of chronic bronchitis:
- Usually Strep. pneumoniae or H. influenzae - Bronchiolitis:
- RSV
4. Pneumonia: Typical (acute onset, severe): - Strep. pneumoniae (80%) - H. influenzae - Klebsiella pneumoniae - Moraxella catarrhalis Atypical (gradual onset): - Mycoplasma pneumoniae, - Legionella - Chalmydophila - Viruses (influenza, adenovirus, RSV, parainfluenza, VZV) - Fungi (histoplasma, aspergillus, pneumocystitis jirovecii)
4
Q
Pathogenesis of pneumonia:
A
- Lungs are constantly exposed to microbes (especially from URT) and sterility is maintained by innate and adaptive immunity
- Pneumonia occurs when there is a defect in host defence, microbe is highly virulent or the infective dose is large
- The route of infection is microaspiration of URT microbiota, direct inhilation and spread to lungs from blood
5
Q
What is the standard emperical treatment for CAP?
A
- PenG/amoxycillin (B-lactam)
+ - Any doxycline/any macrolide e.g. erythromycin
6
Q
How is influenza spread?
A
- Droplet infection from coughing and sneezing
- Virus binds sialic acid-containing receptors (SA a2,6 in humans) on the respiratory tract
7
Q
Describe the structure of influenza A?
A
- Viral envelope: hemagglutinins (HA) and neuraminidase (NA) and M2 proteins on surface
- Matrix proteins under envelope
- 8 ribonucleoproteins inside that contain -ve ssRNA and RNA dependent RNA polymerase subunits
8
Q
Describe the replication cycle of influenza A?
A
- Viral HA binds to a sialic acid 2,6 on the surface of respiratory epithelial cells
- Binding induces receptor-mediated endocytosis
- As endosome migrates into the cell it becomes more acidic and the HA undergoes a confirmational change so it can fuse with the endosome membrane
- Viral HA opens the endosome and the 8 RNPs escape the endosome and enter the nucleus
- The RNPs use their viral RNA polyemerase to generate +ssRNA (mRNA) and replicate their genome
- The viral mRNA is used for viral protein synthesis
- HA and NA are trafficked through the Golgi and onto the cell membrane
- Viral RNPs package together under the cell membrane where HA and NA are expressed
- The RNPs bud out of the cell acquiring an envelope and glycoproteins from the host membrane
- To prevent the new viruses from binding back to the dying cell- the NA cleaves the sialic acid molecules from the dying host cell surface
- Newly formed viruses shed into respiratory lumen and their NA is cleaved by trypase Clara in order to be infectious
9
Q
What is antigenic drift?
A
- The acquisition of mutations within a virus (especially in RNA viruses where polymerase has no proof reading capacity)
- If these mutations are advantageous (e.g. are in the site where neutralising antibodies bind NA or HA) they may be selected for
- Leads to the development of new strains within a flu subtype
10
Q
What is antigenic shift?
A
- The sudden appearance of a influenza A virus with new HA (and sometimes NA) within the human population
- Results in rapid spread and mortality (pandemic) as there is no Ab immunity in the population
- Can occur due to mixing of influenza viruses in a “mixing vessel” such as a pig- the new virus will have avian HA and NA and human internal genes
11
Q
What factors predispose a person to developing a LRI?
A
- Smoking (impairs cilia and alveolar macrophages)
- Viral infection (impairs cilia)
- Cystic fibrosis
- Anaesthetic (impairs cilia)
- Genetic factors
- Oedema in the lungs (impairs alveolar macrophages)
12
Q
What are the 3 types of inflammation that can occur in pneumonia and their likely pathogens?
A
- Acute (typical):
- Strep. pneumoniae
- H. influenzae
- Klebsiella pneumoniae
- Strep. pyogenes
- Staph. aureus
- Other gram -ves - Chronic (atypical):
- Mycoplasma pneumoniae
- Chlamydophila pneumoniae
- Legionella - Granulomatous:
- Mycoplasma tuberculosis
13
Q
What is seen histologically in typical pneumonia?
A
- Acute inflammatory exudate (many neutrophils)
- Fibrin exudate
- Vasodilation
14
Q
What are the 2 patterns of typical pneumonia?
A
- Bronchopneumonia:
- Primary spread along airways with patchy involvement of alveoli
- Dull to percussion + bronchial breath sounds - Lobar pneumonia:
- Spread from alveolus to alveolus
- Pale consolidations seen on CXR + dull to percussion + brochial breath sounds
15
Q
What are the main complications of typical pneumonia?
A
- Hypoxaemia/respiratory failure:
- Severe gas exchange and ventilatory defect leads to decrease in O2
- Hyperventilation occurs to try and correct this
- Respiratory muscles fatigue - Local necrosis and ongoing inflammation:
- Forming a mass lesion in parenchyma: abscess
- Creating a hole: bronchopleural fistula
- Distension and destruction of airways (bronchiectasis) - Spread into pleural space
- Empyema - Spread into blood:
- Bacteremia
- Septic shock
