Staphylococcus aureus bacteraemia

Question 1

Which two mechanisms can S aureus cause disease?

Answer 1

1) Toxin mediated

2) Non-toxin mediated

Question 2

Microbiology of S aureus?

Answer 2

• Gram positive cocci
• Clusters
• Catalase positive
• Coagulase positive
• B haemolytic

Question 3

What percentage of individuals are colonised with S aureus in healthy persons?

Answer 3

25-50% of healthy persons

Question 4

Which populations have a higher rate of colonisation of S aureus?

Answer 4

• Insulin-dependant diabetics
• HIV positive
• Patients undergoing haemodialysis
• Individuals with skin damage

Question 5

What is the most common site of colonisation of S aureus?

Answer 5

The anterior nares

Question 6

What sites are commonly colonised with S aureus?

Answer 6

• Anterior nares = Most common
• Skin
• Vagina
• Axilla
• Perineum
• Oropharynx

Question 7

What do sites of colonisation act as in terms of future infection?

Answer 7

A reservoir

Question 8

Are you at higher risk of infection if colonised with S aureus?

Answer 8

Yes

Question 9

Classifying S aureus bacteraemia

Answer 9

Environment:

• Healthcare acquired
• Community acquired

Absence or presence of identified associated sites of infection:

• Primary
• Secondary

Question 10

Spectrum of S aureus infection?

Answer 10

1) Skin and soft tissue infections - S aureus is the most common agent
2) Localised pyogenic staph infections - furuncles and carbuncles
3) Deep-seated abscesses, necrotising fasciitis, pyomyositis
4) Osteomyelitis, septic arthritis, discitis
5) Infective endocarditis
6) Pneumonia, empyema
7) HAI - Vascular line, catheter, ventilation

Question 11

Localised pyogenic Staph?

Answer 11

Furuncles and carbuncles

Question 12

Musculoskeletal and S aureus?

Answer 12

• Deep seated abscesses
• Necrotising fasciitis
• Osteomyelitis
• Septic arthritis
• Discitis

Question 13

The respiratory system and S aureus?

Answer 13

• Pneumonia

- Empyema

Question 14

The heart and S aureus?

Answer 14

Infective endocarditis

Question 15

What percentage of patients with S aureus bacteraemia develop local complication or distant septic metastases?

Answer 15

Approx 33%

Question 16

What are the frequent sites of distant metastases in S aureus bacteraemia?

Answer 16

• Bones and joint, especially prosthetic materials
• Epidural space and intervertebral discs
• Native and prosthetic cardiac valves, cardiac devices
• Visceral accesses in spleen, kidney and lungs

Question 17

Which investigations may be used in S aureus bacteraemia?

Answer 17

• Microscopy and culture of specimens
• Multiple blood cultures before commencing antibiotic therapy
• Repeat blood cultures are recommended 49-72hours after commencing antimicrobial therapy
• Biopsy sample may be of value in bone infections
• Imaging = Radiograph, CT, MRI, radionuclide imaging
• Transthoracic echocardiography, TOE

Question 18

What are the basis of management in invasive Staph infections?

Answer 18

1) Antibiotic therapy
2) Source identification and clearance
3) Appropriate surgical intervention

Delayed administration after 72-96hrs is associated with in increased in mortality and complications

Question 19

Antibiotic choice for uncomplicated S aureus bacteraemia?

Answer 19

Flucloxacillin for a minimum of 14 days

Question 20

Why is vancomycin not an ideal drug for S aureus bacteraemia?

Answer 20

• Poor tissue penetration
• Slow bactericidal activity
• Inconvenient administration
• Side effects

Question 21

Advantage of using Teicoplanin in S aureus?

Answer 21

• Single daily dosing

- Can be used as little as three times weekly after appropriate loading

Question 22

What complication of S aureus bacteraemia may Linezolid be a choice for treatment?

Answer 22

Osteomyelitis due to is good penetration into bone and excellent oral bioavailability

Question 23

What is Linezolid?

Answer 23

A bacteriostatic, synthetic oxazolidinone antibacterial

Question 24

What is Deptomycin?

Answer 24

A cyclic lipopeptide antibacterial

Question 25

What I the advantage of using daptomycin in S aureus bacteraemia?

Answer 25

- Rapid bactericidal activity against S aureus - Well tolerated - Once daily dosing

Question 26

Imaging in osteomyelitis?

Answer 26

MRI, CT, nuclear medicine

Question 27

What to do when indwelling IV device and S aureus infection?

Answer 27

1) Remove device 2) Blood cultures 3) 2 weeks IV treatment

Question 28

How to treat osteomyelitis?

Answer 28

Minimum 2 weeks IV therapy + at least 4 further weeks of IV/oral

Question 29

How to treat septic arthritis?

Answer 29

Minimum 2 weeks IV therapy + at least 2 further weeks of IV/oral

Question 30

Initial management in Staph bacteraemia ??

Answer 30

1) Check for signs of sepsis, initiate fluid resuscitation if required 2) Blood cultures prior to antibiotics 3) Prompt administration of empirical antibiotic therapy: - If MSSA = IV flucloxacillin 2g 4-6 hourly - If MRSA, or penicillin allergy = Local vancomycin protocol 4) Look for potential site of infection, consider recent medical history 5) Consider need for further microbiology samples if evidence of infection 6) Consult senior clinicians 7) Repeat blood cultures in 48-96 hours and if ongoing fever despite antibiotic therapy

Question 31

Vancomycin therapy in S aureus?

Answer 31

Used when: - Allergic to penicillin - MRSA 1) Intermittent infusion - Aim for trough of 15-20 mg/L 2) Continuous infusion - Aim for steady state concentration of 20-25mg/L