Staphylococcus aureus bacteraemia Flashcards
Which two mechanisms can S aureus cause disease?
1) Toxin mediated
2) Non-toxin mediated
Microbiology of S aureus?
- Gram positive cocci
- Clusters
- Catalase positive
- Coagulase positive
- B haemolytic
What percentage of individuals are colonised with S aureus in healthy persons?
25-50% of healthy persons
Which populations have a higher rate of colonisation of S aureus?
- Insulin-dependant diabetics
- HIV positive
- Patients undergoing haemodialysis
- Individuals with skin damage
What is the most common site of colonisation of S aureus?
The anterior nares
What sites are commonly colonised with S aureus?
- Anterior nares = Most common
- Skin
- Vagina
- Axilla
- Perineum
- Oropharynx
What do sites of colonisation act as in terms of future infection?
A reservoir
Are you at higher risk of infection if colonised with S aureus?
Yes
Classifying S aureus bacteraemia
Environment:
- Healthcare acquired
- Community acquired
Absence or presence of identified associated sites of infection:
- Primary
- Secondary
Spectrum of S aureus infection?
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
Localised pyogenic Staph?
Furuncles and carbuncles
Musculoskeletal and S aureus?
- Deep seated abscesses
- Necrotising fasciitis
- Osteomyelitis
- Septic arthritis
- Discitis
The respiratory system and S aureus?
- Pneumonia
- Empyema
The heart and S aureus?
Infective endocarditis
What percentage of patients with S aureus bacteraemia develop local complication or distant septic metastases?
Approx 33%
What are the frequent sites of distant metastases in S aureus bacteraemia?
- 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
Which investigations may be used in S aureus bacteraemia?
- 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
What are the basis of management in invasive Staph infections?
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
Antibiotic choice for uncomplicated S aureus bacteraemia?
Flucloxacillin for a minimum of 14 days
Why is vancomycin not an ideal drug for S aureus bacteraemia?
- Poor tissue penetration
- Slow bactericidal activity
- Inconvenient administration
- Side effects
Advantage of using Teicoplanin in S aureus?
- Single daily dosing
- Can be used as little as three times weekly after appropriate loading
What complication of S aureus bacteraemia may Linezolid be a choice for treatment?
Osteomyelitis due to is good penetration into bone and excellent oral bioavailability
What is Linezolid?
A bacteriostatic, synthetic oxazolidinone antibacterial
What is Deptomycin?
A cyclic lipopeptide antibacterial
What I the advantage of using daptomycin in S aureus bacteraemia?
- Rapid bactericidal activity against S aureus
- Well tolerated
- Once daily dosing
Imaging in osteomyelitis?
MRI, CT, nuclear medicine
What to do when indwelling IV device and S aureus infection?
1) Remove device
2) Blood cultures
3) 2 weeks IV treatment
How to treat osteomyelitis?
Minimum 2 weeks IV therapy + at least 4 further weeks of IV/oral
How to treat septic arthritis?
Minimum 2 weeks IV therapy + at least 2 further weeks of IV/oral
Initial management in Staph bacteraemia ??
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
Vancomycin therapy in S aureus?
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
