Staph Aureus Bacteraemia

Question 1

Where does staph aureus rank by levl of virulence of staphylococcal species?

Answer 1

Most virulent

Question 2

Through what mechanisms can staph aureus cause disease?

Answer 2

Both toxin-mediated and non-toxin mediated mechanisms

Question 3

Is staph aureus part of the normal human flora?

Answer 3

Yes

Question 4

What kind of bacteria is staph aureus?

Answer 4

Gram-positive cocci

forma grape like clusters on gram stain

Question 5

Is colonisation of staph aureus normal?

Answer 5

• 25-50% of healthy people have persistent or transient colonisation
  
  • Rate is higher amount patients within insulin dependent diabetes, HIV patients, haemodialysis patients and people with skin damage

Question 6

What is the most frequent site of staph aureus colonisation?

Answer 6

Anterior nares:

• Skin, vagina, axilla, perineum and oropharynx can also be colonised

Question 7

Are patients with colonisation at greater or less risk of future infection?

Answer 7

Greater risk

Question 8

What are S. Aureus bloodstream infections classified according to?

Answer 8

Classified according to environment of acquisition:

• Healthcare associated or
• Community acquired

Or absence or presence of identified associated sites of infection:

• Primary or
• Secondary

Question 9

33% of patients with S. Aureus bacteraemia develop local or distant septic metastases, what are some common sites?

Answer 9

• Bones and joints
• Epidural space and intervertebral discs
• Native and prosthetic cardiac valves
• Visceral abscesses in spleen, kidneys and lungs

Question 10

S. Aureus can cause many infections, what are some examples?

Answer 10

• Skin and soft tissue infection
  
  • S. Aureus is most common agent
• Localised pyogenic staph infections
• Deep seated abscesses, necrotising fasciitis, pyomyositis
• Osteomyelitis, septic arthritis, discitis
• Infective endocarditis
• Pneumonia, empyema
• In hospital, wound infection or catheter related infection

Question 11

What investigation is done for S. Aureus bacteraemia?

Answer 11

• Multiple blood cultures before commencing antibiotic therapy
• Repeat blood cultures 48-72 hours after commencing antimicrobial therapy
• Biopsy for bone infections
• Imaging
  
  • X-ray
  • CT
  • MRI
  • Radionuclide imaging
• Transthoracic echocardiography

Question 12

What is the basis of treatment for an invasive staph aureus infection?

Answer 12

• Antibiotic therapy
• Source identification and clearance
• Appropriate surgical intervention

Question 13

What is delay of therapy for an invasive staph aureus infection associated with?

Answer 13

Higher risk of complications and mortality

Question 14

Describe the possible antibiotic management of a staph aureus infection?

Answer 14

• Flucoxacillin (first choice)
  
  • Minimum duration of treatment for uncomplicated staph aureus bacteraemia is 14 days
• Vancomycin (used if allergic to penicillin)
  
  • Not ideal due to poor tissue penetration, slow bactericidal activity, inconvenient administration and side effects
• Teicoplanin
  
  • Advantage is only single daily dose
• Linezolid
  
  • Bacteriostatic, synthetic oxazolidnone, good pentration into bone and good oral bioavailability
• Daptomycin
  
  • Only one dose a day and well tolerated, rapid bactericidal activity against staph aureus