S. aureus

[Clin Infect Dis 2023, ciad500]

Jump to Therapy

- S. aureus in blood cultures should always be considered clinically significant and investigated and treated promptly.

- S. aureus bacteremia (SAB) is associated with significant morbidity and a 20-40% risk of mortality.

Risk factors:

• injection drug use

• prosthetic devices, e.g. orthopedic implants, vascular catheters, pacemakers, intra-cardiac devices

Management:

1. An Infectious Diseases (ID) consult is strongly recommended as ID involvement is associated with improved patient outcomes, e.g. decreased mortality and relapse rates; and improved identification of metastatic infections. PET/CT may be superior in finding metastatic foci especially in patients with prolonged bacteremia and/or prosthetic medical devices. 

2. Thorough patient history and physical exam to determine the source of SAB and identify metastatic infection, e.g. vertebral osteomyelitis, epidural, psoas, or other abscesses, septic arthritis, septic pulmonary emboli.

3. Echocardiogram to rule out endocarditis:

• TEE preferred over TTE if:

  • metastatic infection

  • prosthetic valve or devices, or hemodialysis access

  • prolonged bacteremia (> 4 days)

  • community-acquired bacteremia – positive blood culture within 48 hours of admission and no prior healthcare contact

• TEE if TTE not helpful or poor visualization with TTE

4. Source control – remove infected prosthetic devices and drain abscesses wherever possible

5. Repeat blood cultures every 48-72h until two consecutive negative blood cultures (to account for skip phenomenon). Duration of therapy should start from date of first negative blood culture:

• Uncomplicated/low risk SAB (no predisposing host factors, no endocarditis/negative TTE, hospital-acquired bacteremia, no prosthetic devices, no metastatic infection, defervescence within 72 hours of active antibiotic therapy, and negative blood cultures at ≤ 48-72 hours): 14 days

• Complicated/high risk SAB (endocarditis, prosthetic devices, metastatic infection, history of IDU and/or endocarditis, persistent fever or bacteremia at > 48-72 hours despite active antibiotic therapy): 4-6 weeks

NB: Central line/PICC insertion should be delayed until blood cultures are negative.

Do NOT use oral antibiotics at any point for SAB.

Gram positive cocci in clumps/clusters

Cloxacillin susceptible (MSSA)

Cloxacillin resistant (MRSA)

Vancomycin MIC ≤ 2µg/mL

Intolerant to Vancomycin or MRSA with vancomycin MIC > 2µg/mL