Staphylococcus aureus Bacteraemia

Question 1

Staphylococcus aureus facts (5)

Answer 1

Most virulent of the many staphylococcal species.

Remains a major cause of morbidity and mortality.

Causes disease through both toxin-mediated and non-toxin-mediated mechanisms.

Responsible for both healthcare associated and community-based infections.

S.aureusis a part of the normal human flora.

Question 2

How does staph A cause disease

Answer 2

through both toxin-mediated and non-toxin-mediated mechanisms.

Question 3

S.aureusis a part of the?

Answer 3

normal human flora

Question 4

Staphylococci are

Answer 4

Gram-positive cocci that form grape-like clusters on Gram stain.-PURPLE

Question 5

Where is the rate of colonisation greater (4)

Answer 5

among patients with insulin-dependent diabetes, HIV infection, patients undergoing haemodialysis, and individuals with skin damage.

Question 6

Where are the most frequent sites of colonisation.

Answer 6

Anterior nares

Question 7

Where else can it colonise?

Answer 7

Skin (especially when damaged), vagina, axilla, perineum, and oropharynx may also be colonised.

Question 8

These colonisation sites serve as a

Answer 8

reservoir for future infections

Question 9

Persons colonised withS. aureusare at greater risk of ?

Answer 9

of subsequent infection than uncolonised individuals.

Question 10

S. aureus Blood stream infections are classified by?

Answer 10

environment of acquisition
healthcare associated or
community acquired

Question 11

Absence or presence of identified associated sites

of infection can be

Answer 11

primary or secondary

Question 12

Spectrum of infection

Answer 12

vast - could be a boil

Question 13

What agent causes the most common infections

Answer 13

Skin & Soft Tissue Infections- S. aureusis the most commonly identified agent.

Question 14

Where else can you see S.Aureus infections (5)

Answer 14

Localised pyogenic staphylococcal infections- furuncles and carbuncles.

Deep-seated abscesses, necrotising fasciitis, pyomyositis

Osteomyelitis, Septic arthritis, Discitis

Infective endocarditis

Pneumonia, Empyema

In the hospital setting- wound infection

Question 15

Approximately one-third of patients with S.aureus

bacteraemia develop?

Answer 15

local complications or distant

septic metastases.

Question 16

Frequent sites of distant metastases (4)

Answer 16

Bones and joints (especially when prosthetic materials are present)
Epidural space and intervertebral discs
Native and prosthetic cardiac valves, Cardiac devices
Visceral abscesses in spleen, kidneys and lungs

Question 17

Investigations (6)

Answer 17

Microscopy and culture of specimens.
multiple blood cultures before commencing antibiotic therapy.
Repeat blood cultures are recommended 48–72 hours after commencing antimicrobial therapy.
Biopsy samples may be of value for bone infections
Imaging- X-ray, CT, MRI, Radionuclide imaging
Transthoracic echocardiography, TOE

Question 18

How many blood cultures before antibiotic therapy

Answer 18

2

Question 19

Biopsy …

Answer 19

especially if blood culture is negative

Question 20

Management Basis of treatment for invasive staphylococcal infections- (3)

Answer 20

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

Question 21

What is associated with with an increased risk of complications and higher mortality?

Answer 21

Delay in the administration of appropriate antibiotic
therapy and persistent bacteraemia after 72–96 hours of
appropriate therapy

Question 22

Antibiotic management (5) - timings of drugs/managements

Answer 22

Flucloxacillin- minimum duration of treatment for uncomplicatedS. aureusbacteraemia is 14 days. IV therpay

Vancomycin- far from an ideal drug due to poor tissue penetration, slow bactericidal activity, inconvenient administration and side effects. First line for MRSA

Teicoplanin- has an advantage in terms of its single daily dosing and could also be used three times weekly after appropriate loading

Linezolid- bacteriostatic, synthetic oxazolidinone, good penetration into bone and excellent oral bioavailability.

Daptomycin- cyclic lipopeptide with rapid bactericidal activity againstS. aureus. Well tolerated. Has the advantage of once daily dosing. Good for people with difficult venous access.