Infections of Respiratory System

Question 1

What is the Common Cold?

Answer 1

Symptoms:
Sneezing, congestion, fever, malaise etc.

Caused by: Rhinovirus

Pathogenesis:
Rhinoviruses attach to ICAM-1 located in cells lining the nasal cavity. Viruses cause cells to synthesise new virus particles. Infected cells lose ciliary action and die.
–> triggers release of inflammatory cytokines & stimulates nerve endings - results in cold symptoms
i.e sneezing, increased mucous production & inflammation –> which lead to congestion.
Cold viruses live at 33 degrees C. (Temp of nasal cavity) - so do not move to lower respiratory tract.

Diagnosed by: Symptoms

Treated by: Supportive Care

Question 2

What is the Flu?

Answer 2

Symptoms: Flu like symptoms i.e similar to cold. Congestion, sneezing, fever, malaise etc.

Caused by: Influenza virus a, b, c

Pathogenesis:
Infects upper resp. tract via HA (hemoagglutinin) envelope protein and NA (neuraminidase) –> virus replicates and lyses cells leading to necrosis of epithelium which stimulates inflammatory response. Macrophages produce IL causing vasodilation & edema

Diagnosed by: Symptoms or antigen

Treatment: Supportive

Prevention: Vaccine - inactivated.
Live attenuated.

Question 3

What is Tuberculosis?

Answer 3

Symptoms: - Lack of appetite and weight loss

• Fever
• Night sweats
• Malaise
• Persistent cough/ breathlessness

Caused by: Mycobacterium tuberculosis

Pathogenesis:
Infection spreads through respiratory route –> droplets with tubercle bacilli are inhaled. –> Macrophages in alveoli phagocytose M. tuberculosis, however they survive and replicate within endosome of macrophage.
Cell mediated immunity produce lymphokines and causes infiltration of infected macrophages –> with development of granulomas.
Other immune cells react by depositing collagen that enclose the macrophage within hard nodular tubercles - infected cells in the centre die (Caseous necrosis) and are surrounded by an outer layer of connective tissue cells.

The primary infection heals often without causing symptoms - the infected person then has life long immunity to the disease.

Complications:
If bacteria get into bloodstream –> can spread
- Infection may break into pleural space - causing a pleural effusion (seen on X-Ray)
- Primary infection may spread through body causing military TB
- TB meningitis

Diagnosed by: CXR, Mantoux Test, Skin delayed hypersensitivity to tuberlin
- Latent TB
Other TB: CT scan and blood test.

Treatment: Long term antibiotic regime: 
4 Antibiotics: 
For 6 months:
- Rifampicin
- Isoniazide
For first 2 months:
- Ethambutol
- Pyrazinamide

Prevention:
BCG vaccine - live attenuated (Usually to prevent against Miliary TB and TB meningitis)
Prevent spread - isolate patients during infective stage.

Question 4

What is Secondary TB?

Answer 4

• Occurs when M. tuberculosis ruptures the tubercle & re-establishes the infection.

Question 5

What is Disseminated TB?

Answer 5

• Occurs when infected macrophages carry bacteria elsewhere systemically

Question 6

What is a Scrofula?

Answer 6

Cervical lymph node TB infection

Question 7

Give a general definition of Pneumonia.

Name some symptoms, its pathogenesis and how it might be diagnosed.

How many types of Pneumonia are there? (Broadly) What are they?

Answer 7

Pneumonia results from pulmonary inflammation & accumulation of fluid in the alveoli and bronchioles of the lungs.

Symptoms:

• Chest pain
• Confusion
• Productive cough
• Fatigue
• Fever/sweating/chills
• Lower than normal body temperature
• Nausea vomiting or diarrhoea
• SOB
• Neonates may be asymptomate - or have fever & difficulty in breathing and eating.

Pneumonia starts as an URTI that moves into lower resp tract to cause inflammation of the lung.

Diagnosed by: Physical examination & CXR (will see consolidation)
Blood tests & culture to identify organism

5 Types:

1. Community acquired pneumonia (CAP)
2. Hospital acquired pneumonia (HAP)
3. Aspiration pneumonia
4. HIV associated pneumonia
5. Atypical pneumonia

Question 8

Tell me about Community Acquired Pneumonia.

What are common causes? (microorganisms)

Answer 8

• One of the most common types
• Acquired within community (outside hospital setting)
• Often follows a viral infection such as the flu

Common causes:

• Streptococcus pneumonia (most common) (can affect one lobe of lung (lobar pneumonia)
• Haemophilus influenza
• Mycoplasma pneumoniae
• chlamydia pneumoniae
• Fungal infections in patients with chronic conditions
• Viruses that cause Resp tract. infections i.e RSV and influenza

Question 9

What is Hospital Acquired Pneumonia (HAP)?

What are common causes? (microorganisms)

Answer 9

Pneumonia that occurs 48 hours + after admission, but was not already incubating.

Causes:

• S. aureus (often resistant)
• Pseudomonas aerguinosa
• Klebsiella pneumonia
• Haemophilus influenza

Viral:

• Influenza
• Cytomegalovirus
• Respiratory syncytial virus

Question 10

What is health/hospital care associated pneumonia (HCAP)?

Answer 10

Bacterial infection that occurs in people who live in long-term care facilities or who receive care in out-patient clinics, including kidney dialysis centres. Can be caused by bacteria that are resistant to antibiotics.

Question 11

What is Ventilator Associated Pneumonia (VAP)?

Answer 11

Pneumonia that arises more than 48-72 hours after endotracheal intubation.

Question 12

What is Aspirational Pneumonia?

What are its common causes? (Microorganisms)

Answer 12

Food, drink, saliva gets into lungs. 
More common if something disturbs normal gag reflux. Common in: 
- Brain injury/ stroke patients
- Alcoholics
- Drug addicts

Common causes:

• Streptococcus pneumonia
• Staphylococcus aureus
• Haemophilus influenza
• Pseudomonas aerguinosa
• Klebsiella pneumonia
• some anaerobes

Question 13

What is HIV associated? Common causes? Pathogenesis?

Answer 13

Pneumonia that is commonly seen in HIV sufferers.

Causes include:

• Pneumocystitis jirovecii
• Cytomegalovirus

Pathogenesis:
P. jirovecii damages interstitial fibrous tissue of the lungs –> causes thickening of alveolar septa and alveoli –> leads to hypoxia.

Question 14

What is Atypical Pneumonia ( AKA Legionnaire’s Disease)?

Answer 14

Form of pneumonia caused by any type of Legionella - mostly commonly Legionella pneumophila

Pathogenesis: Invades and replicates inside macrophages. Bacteria surround themselves in a membrane-bound vacuole that does not fuse with lysosomes that would otherwise degrade the bacteria. Bacteria multiply.

Question 15

What is CURB65? What are the principles?

Answer 15

CURB65 is a score for pneumonia severity.

C = Confusion (New mental confusion)  
U = Urea >7 mmol /l 
R = Respiratory Rate > 30/min 
B = Systolic BP <90mmHg (or Diastolic <60mmHg) 
65 = Those 65+ age

As score increases, risk of death increases.
ScoreS:
0-1: Treat as an outpatient
2: Consider a short stay in hospital or watch very closely as an outpatient
3-5: Requires hospitalization with consideration as to whether they need to be in the intensive care unit

Question 16

What is Otitis Media?

Answer 16

Symptoms:

• Earache
• Fever
• Lethargy
• Slight hearing loss
• Nausea/vomiting

Caused by: Multiple organisms that cause resp. tract infections

Pathogenesis: Most middle ears infections occur when an infection such as a cold leads to a build up of mucus in middle ear –> causes the Eustachian tube to become swollen or blocked.
This means mucus can’t train away properly, making it easier for infection to spread to the middle ear.

Diagnosed by: 
Ear examination (Otescope) showing:
- bulging
- unusual colour (red or yellow)
- cloudy appearance

Treatment: Supportive/may require antibiotics