Resiratory tract infections tutorial

Question 1

․․․ remains the most commonly identified pathogen in community-acquired pneumonia.

Answer 1

St pneumoniae

Question 2

Other pathogens have been reported to cause pneumonia in the community and include…

Answer 2

Haemophilus influenzae, Mycoplasma pneumoniae, and influenza A, along with newer pathogens such as Legionella species and Chlamydophila pneumoniae. Other common causes in the immunocompetent patient include Moraxella catarrhalis, Mycobacterium tuberculosis, and aspiration pneumonia. The causative agent of community-acquired pneumonia remains unidentified in 30% to 50% of cases

Question 3

The causative agent of community-acquired pneumonia remains unidentified in 30% to 50% of cases.T/F

Answer 3

True

Question 4

purulent sputum, neutrophilia, focal consolidation can also be due to viral pneumonia?

Answer 4

No, it suggests bacterial infection, but the viral infection usually influenza can be complicated by bacterial superinfection and pneumonia.

Question 5

is the presentation of TB acute or chronic?

Answer 5

TB usually presents with more long-standing symptoms

Question 6

what specimens need to be obtained and what investigation s need to be requested in a patient with suspected CAP?

Answer 6

• -Sputum for culture
• -Blood for culture
• -Urine for legionella/pneumococcal antigens
• -Nose/throat swab for influenza PCR - (seasonal)

Question 7

how the sputum is cultured?

Answer 7

Specimen inoculated onto blood and chocolate agar plates and incubated for 18-24 hours

Question 8

what is the goal of chocolate agar?

Answer 8

Blood agar is incubated aerobically and chocolate agar is incubated in CO2 (picks up organisms such as Haemophilus influenzae)

Question 9

name a blood agar plate that contains V-factor (NAD) and X-factor (hematin). Used to culture fastidious bacteria (e.g., Haemophilus influenzae, Francisella tularensis)?

Answer 9

Chocolate agar

Question 10

what pathogen is alpha-hemolytic (greenish discoloration) on blood agar and susceptible to optochin?

Answer 10

Streptococcus pneumoniae

Question 11

Gram-positive cocci in pairs (i.e. diplococci) and short chains are suggestive of …

Answer 11

Streptococci

Question 12

how urinary antigen test is performed?

Answer 12

• -Like a pregnancy test
• -Quick- result in 15 mins
• -Useful if positive (but negative in approx. 30% of pneumococcal infections)

Question 13

which empirical antibiotic therapy should be started based on the CURB-65 score?

Answer 13

• -mild (0-1): POamoxicillin, or clarithromycin or doxycycline
• -moderate: IV amoxicillin + PO clarithromycin
• -severe (3-5): IV co-amoxiclav + PO clarithromycin

Question 14

what organisms are covered by amoxiclav vs clarithromycin?

Answer 14

• -Co-amoxiclav (rather than amoxicillin alone) to cover Haemophilus influenzae as well as Str. pneumoniae. Give IV (severe pneumonia, sepsis)- higher dose and gets in faster than if given PO.
• -Clarithromycin to cover atypicals (e.g. Legionella spp.) Very good oral bioavailability so can give orally (PO)

Question 15

what is the CURB-65 score?

Answer 15

A score used to decide whether patients with pneumonia require hospitalization. Confusion, blood urea > 7 mmol/L (20 mg/dL), respiratory rate ≥ 30/min, systolic blood pressure ≤ 90 mm Hg or diastolic BP ≤ 60 mm Hg, and age ≥ 65 years are each assigned 1 point. If the CURB-65 score is ≥ 2, hospitalization is indicated.

Question 16

what is the clavulanate?

Answer 16

A β-lactamase inhibitor used in combination with β-lactam antibiotics (particularly amoxicillin) to prevent bacteria from inactivating the antibiotic.

Question 17

what are the management principles of CAP?

Answer 17

• -Empiric antibiotics as per local guidelines
• -Rationalise with culture results and susceptibilities
• -Vaccinate to prevent future episodes

Question 18

what is the VAP?

Answer 18

A hospital-acquired infection that develops 48 hours after the initiation of mechanical ventilation via either tracheostomy or intubation. Approx. 5–10% of patients on mechanical ventilation develop VAP.

Question 19

what are the pathogens involved in VAP?

Answer 19

1) Gram- negative bacilli: including multidrug resistant ones
- -E. coli
- -Klebsiella spp.
- -Enterobacter spp.
- -Pseudomonas spp.
- -Serratia marcescens
2) Staphylococcus aureus including MRSA
3) Legionella pneumophila (aerosol inhalation)
4) Anaerobes, e.g. Bacteroides fragilis (aspiration)
6) Viruses: influenza, RSV etc.
7) Fungi e.g. aspergillus (in significantly immunosuppressed patients)

Question 20

Is candida likely to be the cause of the VAP?

Answer 20

Candida spp. often grow from respiratory specimens of intubated patients but almost always represent colonization, not infection

Question 21

what specimens need to be obtained and what investigation s need to be requested in a patient with suspected VAP?

Answer 21

–Broncho-alveolar lavage for culture
–Consider TB/ respiratory viral PCR/ fungi also
Blood cultures (from central lines as well as peripheral cultures)

Question 22

what is the empiric antibiotic therapy for a patient with VAP?

Answer 22

–N.B. Check previous microbiology; is the patient known to be colonized with resistant organisms e.g. MRSA?*
If not:
–Piperacillin-tazobactam
1)Broad-spectrum Gram-positive and Gram-negative cover, including Pseudomonas aeruginosa
2)Pip-taz is recommended empiric treatment for hospital-acquired pneumonia in many hospitals, including Beaumont
3)Choice of antibiotics in ICU patients is usually discussed with the consultant microbiologist

Question 23

how long is the treatment duration of VAP with Piperacillin-Tazobactam?

Answer 23

Treatment duration usually 7 days, but should be judged on a case-by-case basis

Question 24

What measures can be taken to prevent VAP?

Answer 24

• -Avoid intubation unless necessary
• -Standard precautions e.g. hand hygiene & decontamination
• -Appropriate endotracheal tube cuff size
• -Aspiration of secretions (subglottic secretion drainage)
• -Head of bed elevated at 30-45oC
• -Oral hygiene with chlorhexidine

Question 25

what are the sources of neutropenic sepsis?

Answer 25

1) Respiratory tract infection
- -Community-acquired pneumonia
- -Opportunistic infection of the lungs
- -Viral infection (e.g. influenza, if circulating)
2) Infection at another site (may be breathless as part of the sepsis response)

• Non-infective causes
• -Side-effects of chemotherapy
• -Pulmonary embolus

Question 26

What are the likely pathogens of neutropenic sepsis?

Answer 26

1) CAP pathogens (e.g. Streptococcus pneumoniae) also affect immunocompromised patients)
2) However, these patients are also vulnerable to infection with opportunistic pathogens:
- -Fungi
- -Pneumocystis jirovecii
- -Aspergillus fumigatus
- -Cryptococcus neoformans
- -Viruses
- -Herpes simplex (HSV)
- -Cytomegalovirus (CMV)
- -Mycobacteria
- -Atypical mycobacteria & M. tuberculosis

Question 27

What specimens will you send and what microbiological investigations will you request in a patient with suspected neutropenic fever?

Answer 27

1) Blood cultures
2) Broncho-alveolar lavage
- -Bacterial & fungal culture
- -PCR for P. jiroveci & CMV
- -ZN/auramine stain and mycobacterial culture
- Respiratory virus PCR
- -Galactomannan
3) Blood
- -CMV PCR
- -Galactomannan (metabolite released by Aspergillus in systemic aspergillosis)

Question 28

what is the galactomannan?

Answer 28

A heteropolysaccharide component of the Aspergillus cell wall that is shed during the phase of hyphal growth. It can be detected in a serum or bronchoalveolar lavage sample in patients with invasive aspergillosis.

Question 29

what is the 1,3-β-D glucan test?

Answer 29

• -A test used to diagnose certain invasive fungal infection; β-d-Glucan is a carbohydrate component of cell walls common to many fungal species, including Candida spp., Aspergillus spp., and Pneumocystis jirovecii. Its presence suggests invasive infection.
• -1,3-β-D glucan tests are nearly as sensitive as galactomannan antigen for invasive aspergillosis but have a low specificity because they can also be seen with invasive candidiasis.

Question 30

What empiric therapy should be commenced to a patient with neutropenic fever?

Answer 30

1) Initially manage as neutropenic sepsis
- -Piperacillin-tazobactam plus gentamicin
2) If not responding or results suggest a specific opportunistic infection, the addition of other agents may be appropriate

Question 31

What are the anti-infectives of choice for:

1) Pulmonary/invasive aspergillosis?
2) Pneumocystis jirovecii (carinii) pneumonia (“PCP”)?
3) CMV pneumonitis?

Answer 31

A. Voriconazole (or liposomal amphotericin B)
B. Co-trimoxazole
C. Ganciclovir