staph aureus bacteraemias

Question 1

what is the most virulent of the staphylococcal species

Answer 1

Staphylococcus aureus

major cause of morbidity and mortality

responsible for healthcare and community based infection

Question 2

how does S. aureus cause disease

Answer 2

both toxin mediated and non-toxin mediated mechanisms

part of the normal human flora

Question 3

appearance of Staphylococci

Answer 3

gram +ve cocci
form grape like clusters on gram stain
purple-blue

Question 4

S.aureus colonisation (% of population)

Answer 4

25-50% of healthy people may be persistently or transiently colonised

people colonised w/ S. aureus are at greater risk of subsequent infection than uncolonised individuals

Question 5

when is rate of S.aureus colonisation higher

Answer 5

insulin dependent DM
HIV infection
pts on haemodialysis
individuals w/ skin damage

Question 6

sites of S.aureus colonisation

Answer 6

anterior nares are the most frequent site of colonisation

skin (esp when damaged), vagina, axilla, perineum and oropharynx may also be colonised

colonisation sites act as. a reservoir for future infections

Question 7

classification of S.aureus bloodstream infections

Answer 7

environment of acquisition: healthcare associated or community acquired

absence of presence of identified associated sites of infection: 1y or 2y

Question 8

what types of infection can S.aureus cause

Answer 8

skin and soft tissue infections
localised pyogenic staphylococcal infections - furuncles and carbuncles
deep seated abscesses, necrotising fasciitis, pyomyositis
osteomyelitis, septic arthritis, discitis
infective endocarditis
pneumonia, empyema
wound infection, vascular line infection, catheter related infection

Question 9

what proportion of pts w/ S. aureus bacteraemia develop local complications or distant septic mets

Answer 9

1/3

Question 10

frequent sites of distant mets in S.aureus bacteraemia

Answer 10

bones and joints - esp w/ prosthetic material present
epidural space and intervertebral discs
native and prosthetic cardiac valves, cardiac devices
visceral abscesses in spleen, kidneys and lungs

Question 11

investigations for S.aureus bacteraemia

Answer 11

microscopy and culture of specimens
multiple blood cultures before commencing abx
repeat blood cultures 48-72hrs after starting antimicrobial therapy
biopsy samples in bone infection
imaging

Question 12

imaging for S.aureus bacteraemia

Answer 12

X-Ray 
CT
MRI 
radionuclide imaging
transthoracic echo, TOE

Question 13

basis of treatment for invasive staphylococcal infections

Answer 13

antibiotic infection
source identification and clearance
appropriate surgical intervention

Question 14

what can delay in starting antibiotic therapy lead to

Answer 14

delay in the administration of appropriate abx and persistent bacteraemia after 72-96hrs of appropriate therapy –> increased risk of complications and higher mortality

Question 15

what antibiotics are used in the management of S.aureus infections

Answer 15

flucloxacillin 
vancomycin 
teicoplanin 
linezolid 
daptomycin

Question 16

flucloxacillin for S.aureus infections

Answer 16

minimum duration of treatment for uncomplicated S. aureus bacteraemia is 14 days

Question 17

vancomycin for S.aureus infections

Answer 17

not an ideal drug choice
poor tissue penetration 
slow bactericidal activity 
inconvenient administration 
side effects

Question 18

advantages of teicoplanin for S.aureus infections

Answer 18

single daily dosing

can also be used 3 times weekly after appropriate loading

Question 19

linezolid for S.aureus infections

Answer 19

bacteriostatic
synthetic oxazolidinone
good penetration into bone
excellent oral bioavailability

Question 20

daptomycin for S.aureus infections

Answer 20

cyclic lipopeptide
rapid bactericidal activity against S. aureus
well tolerated
once daily dosing