MI: Respiratory Tract Infections Pt.2

Question 1

How does Legionella pneumonia appear on CXR

Answer 1

Bilateral interstitial shadowing

Question 2

What medium is Legionella grown on?

Answer 2

Buffered charcoal yeast extract

Question 3

How is Legionella pneumoniae diagnosed and treated

Answer 3

Diagnosed by urine antigen detection
Treated with macrolides
(Azithromycin)

Question 4

What is a feature of bacteria that cause atypical pneumonia and how does it affect treatment?

Answer 4

They have NO cell wall
Therefore not susceptable to cell wall targetting antibiotics e.g. penicillins

Question 5

List four atypical organisms.

Answer 5

• Mycoplasma pneumoniae
• Legionella pneumophilia
• Chlamydia psittaci
• Coxiella burnetii (Q fever)

Question 6

Which type of antibiotics do work on atypical bacteria?

Answer 6

Antibiotics that interfere with protein synthesis (macrolides, tetracyclines)

Question 7

How is Coxiella burnetii spread and treated

Answer 7

Spread by domestic/farm animals and transmitted by infected aerosol or milk
Treated with doxycycline

Diagnosed on serology

Question 8

How is Chlamydia psittaci spread and treated

Answer 8

Spread from birds by inhalation

Treated with doxycycline

Question 9

Which investigation is used for Coxiella and Chlamydia psittaci?

Answer 9

Serology

NOTE: serology looks at the development of antibodies after an infection. Therefore it requires paired samples (usually collected on presentation and then 10-14 days later)

It is useful for investigating bacteria that are difficult to culture.

Question 10

What is an empyema?

Answer 10

Collection of pus within the pleural cavity

Question 11

List some reasons for failure to respond to treatment.

Answer 11

• Empyema/abscess
• Proximal obstruction (e.g. tumour)
• Resistant organisms
• Not absorbing antibiotics
• Immunosuppression
• Alternative diagnosis (e.g. lung cancer)

Question 12

What is the classical CXR feature of TB?

Answer 12

Upper lobe cavitation

Question 13

What clues in history might point you towards TB?

Answer 13

• Ethnicity/recent travel to endemic regions
• Prolonged course
• Fevers
• Weight loss
• Haemoptysis

Question 14

How is TB diagnosed?

Answer 14

Primary latent TB: TST, IGRA
Active (primary or secondary) TB: PCR, sputum culture, CXR

Question 15

Which types of staining are used when investigating TB?

Answer 15

• Auramine stain
• Ziehl-Neelsen stain

NOTE: they are red rods

Question 16

Define hospital-acquired pneumonia.

Answer 16

A pneumonia that presents > 48 hours after hospital admission

Question 17

List some organisms that cause HAP.

Answer 17

• Enterobacteriaciae 31% (MOST COMMON - e.g. E. coli, K. pneumoniae)
• Staphylococcus aureus 19%
• Pseudomonas 17%
• Haemophilus influenzae
• Acinetobacter baumanii
• Fungi (e.g. Candida)

Question 18

Classical PCP CXR presentation

Answer 18

Bilateral consolidation “Bats wing”