Septic Arthritis

Staphylococcus aureus 

Group A streptococcus 

Kingella kingae in children < 3 years 

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Lyme arthritis is a distinct diagnosis separate from septic arthritis and should be considered in the differential diagnosis for septic arthritis - see subsection below for features that should prompt consideration  

Clinically stable:  

Cefazolin 50 mg/kg/dose (max 2000 mg/dose) IV q8h  

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Severely ill (hemodynamic instability, multiple sites involved, or known positive blood culture for gram- positive organism (while awaiting initial ID and susceptibility):  

Cefazolin 50 mg/kg/dose (max 2000 mg/dose) IV q8h  

AND  

Vancomycin  

(follow link for dosing & monitoring)  

Consult ID for therapy selection if blood culture is positive for a gram-negative organism 

Penicillin or cephalosporin allergy with higher risk for allergic reaction or, clinically stable with history of documented MRSA infection or carriage within the last 6 months 

Please confirm clindamycin susceptibility if prior cultures are available, tailor antibiotics to past susceptibility: 

Clindamycin 13 mg/kg/dose (max 900 mg/dose) IV q8h 

Penicillin or cephalosporin allergy with higher risk for allergic reaction, severely ill (hemodynamic instability or rapid local progression) or known positive blood culture for gram-positive organism (while awaiting initial ID and susceptibility):  

Consult ID 

ID and Orthopedic Surgery consults recommended 

Surgical evaluation is considered urgent for all patients with suspected septic arthritis and is particularly time-sensitive for septic arthritis of the hip, knee or shoulder 

At initial evaluation, send ESR, CRP and blood culture  

Joint aspirate should be performed before antibiotics unless patient is clinically unstable or has known bacteremia (send cell count, routine culture, hold “universal microbial DNA” from fluid) 

If cultures are positive, use results of preliminary diagnostic tests to target therapy 

Duration: Uncomplicated septic arthritis is usually treated for 2-3 weeks, guided by follow-up assessments, with minimum 3 weeks for infection due to S. aureus 

Lyme arthritis 

Distinguishing features of Lyme arthritis of the knee from septic arthritis of the knee in an endemic area include:  

Peripheral blood absolute neutrophil count  <10,000 cells/mm3

AND

ESR < 40 mm/hr 

Additional suggestive features:  
Lower synovial fluid WBC, lack of fever or systemic illness, history of residence or travel to endemic area, greater ability to bear weight 
 
Diagnostic testing: 2 step serology - Lyme EIA, reflex to IgG Western blot if EIA is positive (positive IgM Western blot with negative IgG Western blot is not consistent with this diagnosis) 

Age >=8years: 

Doxycycline 2.2 mg/kg/dose (max 100mg/dose) PO bid  

Age <8 years: Amoxicillin 16.7 mg/kg/dose (max 500mg/dose) PO tid 

ID consult recommended  
 
Lyme arthritis is managed without surgery and does not always necessitate invasive evaluation (joint aspirate); Orthopedic Surgery should be consulted if septic arthritis is also being considered  

Duration: 28 days, with follow-up assessment 

Note that treatment recommendation and duration is specific to Lyme arthritis and not applicable to other manifestations of Lyme disease