Septic Arthritis

Patient Population: Pediatric
Condition Major Pathogens  First-choice Therapy Alternative Therapy Comments
Septic arthritis in child > 3 months old without medical comorbidities or other exception criteria defined below 

Staphylococcus aureus 

Group A streptococcus 

Kingella kingae in children < 3 years 


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  


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  



(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


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) 

Borrelia burgdorferi 

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 

Bone or joint infection in patient with significant medical comorbidities, age 0-3 months, penetrating trauma, orthopedic hardware involved, contiguous infection or other modifying factors Variable based on risk factors  Consult ID for guidance before initiating empiric therapy    ID and Orthopedic Surgery consults recommended 


American Academy of Pediatrics. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2021 Report of the Committee on Infectious Diseases. 32nd ed. Elk Grove Village, IL: American Academy of Pediatrics; 2021.  

Deanehan JK, et al. Distinguishing Lyme from septic knee monoarthritis in Lyme-disease endemic areas. Pediatrics 2013;131:e695-e701.  

Deanehan JK, et al. Synovial fluid findings in children with knee monoarthritis in Lyme disease endemic areas. Pediatr Emerg Care 2014;30:16-19. 

Pediatric Empiric Antimicrobial Therapy Guidelines

This is a subsection of the UCSF Benioff Children’s Hospitals Empiric Antimicrobial Therapy Guidelines, developed by the Pediatric Antimicrobial Stewardship Programs at each campus to inform initial selection of empiric antimicrobial therapy for children at the UCSF Benioff Children’s Hospitals and affiliated outpatient sites. 

These are guidelines only and not intended to replace clinical judgment. Modification of therapy may be indicated based on patient comorbidities, previous antibiotic therapy or infection history. Doses provided are usual doses but may require modification based on patient age or comorbid conditions. Refer to Pediatric Antimicrobial Dosing Guideline for further guidance on dosing in children, and Neonatal Dosing Guideline for infants < 1 month of age. Consult a pediatric pharmacist for individualized renal or hepatic dose adjustment. Durations provided are usual recommendations for patients who are responding appropriately to therapy. For additional guidance, please contact Pediatric Infectious Diseases (ID) or the Pediatric Antimicrobial Stewardship Program (ASP) at the campus where your patient is receiving care.  

For questions or feedback about these guidelines, please email primary content owners, Rachel Wattier, Pediatric ASP Medical Director at BCH SF and Prachi Singh, Pediatric ASP Medical Director at BCH OAK. 

The content of these guidelines was updated in July 2021. See Summary and Rationale for Changes (password login to Box needed) for detailed explanations of the content changes.