Upper Respiratory Tract Infections

Question 1

Upper respiratory Tract normal flora:

1. 4 examples Common residents (<50% of normal people)
2. 2 examples occasional residents (<10% of normal people)
3. 3 examples of organism’s associated with colonization of URT following antibiotic treatment

Answer 1

1. Common residents:

• Viridians streptococci
• Anaerobic microorganisms (e.g. Bacteroides)
• Haemophilus influenzae
• Candida albicans

2. occasional:

• Streptococcus pyogenes (Group A streps)
• Streptococcus pneumoniae

3. Associated with colonization after Antibiotics:

• Coliforms (E-coli)
• Pseudomonas sp..
• Candida albicans (Oral thrush)

Question 2

Professional invaders:

Define a professional invader.
3 main requirements to be a professional invader.

Answer 2

Define a professional invader:
A professional invader can successfully infect the healthy respiratory tract; possess mechanisms to attach and spread (true pathogen)

Three main attributes:

1. Adhesion to normal mucosa (in spite of the mucocilliary system). eg. surface proteins, capsid proteins.
2. Avoid host defenses. (e.g. capsule)
3. Damage local tissue: production of invasins and exotoxins eg. pneumolysin.

Question 3

Secondary invaders:

Define secondary invaders
Examples of when secondary invasion can occur.

Answer 3

Define a secondary invader:
A secondary invader can cause disease when the host defenses are impaired:

• Normal flora C. albicans can over grow post immunodeficiency.

Examples of times secondary invasion can occur:

1. Post viral infection ( e.g. rhinovirus)
2. Compromised immune response. (AIDS, Chemotherapy, young/old, alcoholics).
3. Foreign body: e.g. endotracheal tube.

Question 4

The Common Cold (Coryza): Clinical manifestation:

• Incubation:?
• signs and symptoms: ?
• how complications can arise: ?
• when and who does it affect and how long does it last: ?
• What could be the causative agent:
• Common treatment: ?

Answer 4

• incubation period: 2 - 4 days
• Symptoms: nasal discharge, sneezing and sore throat; sometimes temp and headache.
• Complications can arise from descending infection leading to laryngitis or tracheitis.
• Seasonal: common during winter months, usually affects children 2 -7 but affects all age groups. symptoms last about a week.
• Causative organism: Viruses: e.g. Rhinovirus (>100 types), Respiratory syncytial virus (RSV), Coronavirus.

Treatment: supportive eg paracetamol. Antibiotics ARE NOT indicated for common colds.

Question 5

CANDIDIASIS (THRUSH) Clinical manifestation:

What causes fungi overgrowth brief. what are the classical symptoms.

Predisposing factors:

Causative agent:

Treatment:

Answer 5

Clinical manifestation:

Changes in flora can upset the balance allowing for overgrowth of fungi.

Symptoms: Raw inflamed mucous membranes, white fungal plaques.

Predisposing factors: Broad spectrum antibiotics; Contraceptive pill, systemic steroids’, chemotherapy, immunosuppression.

Causative agent: Candida albicans

Treatment:
1. Nystatin or clotrimazole pastilles, 1 pastille QDS (up to 7 days)

2. Severe oral thrush in HIV patients may need treatment with a systemic antifungal drug eg. fluconazole 100mg (14-30 days)

Question 6

Sinusitis:

Clinical manifestation: signs and symptoms?

Causative agent:

Treatment:

Answer 6

Clinical manifestation:
- Facial pain, localized tenderness and swelling.

Causative agent: Usually viral but bacterial infection may occur due to secondary invaders Strep pneumoniae and Haemophilus influenzae.

Treatment:

• no treatment for viral infection.
• A culture of sinus washout should support the clinical diagnosis.

Bacterial treatment:
1. Amoxicillin 125-250mg tds (3-7 days)

2. Augmentin (co-amoxiclav) for beta lactamase producing bacteria 250mg tds (3-7 days)
3. Doxycycline 100mg daily (3-7days)
4. Erythromycin 250-500 mg qds (3-7 days)

Question 7

Pharyngitis/Tonsillitis:

Clinical manifestation: Signs and symptoms.

Causative agent: Virus/bacterial

Treatment: Viral/bacterial

Answer 7

Clinical manifestations: - Common in children, fever, sore throat, cervical lymphadenopathy (neck lymph node swelling) purulent discharge.

Causative agent:
1. virus: main cause (~70%) eg. adenovirus.

2. Bacterial: Streptococcus pyogenes (Common) Neisseria gonorrhoeae (rare).

Treatment:
1. Viral: no treatment.

2. Bacterial:
   - Penicillin V 500 mg qds/10days
   - Cephalexin 500 mg qds/10 days
   - Erythromycin 500mg qds/10days

Question 8

Streptococcal Tonsillitis Complications:

4 complications that can arise

Answer 8

1. Peritonsillar abscess (PTA/Quinsy) Abscess that can cause airway blockage.
2. Rheumatic Fever (Autoimmune)
3. Glomerulonephritis (Autoimmune)
4. Scarlet fever (Toxin-associated)

Question 9

Streptococcus pyogenes (Group A strep): 
Mechanism of pathogenesis: Adhesion: 

2 Proteins involved and what do they bind:

approx how many immunotypes and this means what?

Answer 9

1. Surface expressed F-protein recognizes host cell fibronectin eg. pharynx
2. M-protein is anchored in cytoplasmic membrane and protrudes as fimbriae/pili. Expressed along with Lipoteichoic Acids (LTA). Mediates adherence to epithelial cells/exocellular matrix.
   - >80 distinct immunological types (re-infection is common)
   - Highly antigenic.

Question 10

Evasion of host defense:

• Hyaluronic Acid Capsule
• Immunoglobulin binding proteins
• C5a peptidase

Answer 10

• Hyaluronic Acid Capsule is identical to human substance meaning it can avoid detection; binds to cellular hyaluron receptor CD44 mediating adherence and invasion.
• Immunoglobulin binding proteins: binds Fc region of IgA and IgG preventing opsonization.
• C5a peptidase: surface protein that inactivates C5a (a potent chemotactic peptide) thus limiting the recruitment of polymorphonuclear leukocytes (neutrophils etc) to infection site.