In a child with fever, irritability, and a red, warm, painful, tender swelling of the lower left leg without abscess, stable vital signs and no other systemic findings, what is the appropriate initial management: oral flucloxacillin with topical antibiotics, oral flucloxacillin with follow‑up, or intravenous antibiotics with surgical consultation?

Management of Pediatric Lower Leg Cellulitis with Fever

This child requires intravenous antibiotics with surgical consultation (Option C), as the enlarging area of infection with fever and irritability suggests evolving cellulitis that may harbor a subperiosteal abscess or early osteomyelitis, both of which demand urgent assessment for surgical drainage and parenteral therapy.

Clinical Recognition and Risk Stratification

The presentation of fever, irritability, and an enlarging red, warm, painful area without visible pus strongly suggests moderate-to-severe cellulitis that may be complicated by deeper infection 1, 2. Key features that elevate concern include:

• Fever with irritability in a child indicates systemic involvement and potential bacteremia 1, 2
• Enlarging erythema despite stable vitals suggests progressive infection that may not respond adequately to oral therapy 3
• Absence of visible abscess does not exclude subperiosteal collection, which occurs in up to 50% of late-presenting pediatric osteomyelitis and requires ultrasound or MRI for detection 4, 1
• Pain and tenderness in the lower leg (particularly over long bones) raises concern for underlying osteomyelitis, where the typical triad of fever, pain, and diminished mobility is present in only ~50% of cases 1

Why Intravenous Antibiotics Are Necessary

Oral flucloxacillin (Options A and B) is insufficient for this presentation because:

• The child has systemic signs (fever, irritability) indicating moderate-to-severe infection requiring parenteral therapy 3, 2
• Enlarging cellulitis suggests inadequate host response and potential for rapid progression to necrotizing infection or sepsis 5, 6
• Oral beta-lactams like flucloxacillin have poor oral bioavailability (<80%) and should not be used for initial treatment of serious infections 7
• The CHOICE trial (2019) demonstrated that even for uncomplicated moderate-to-severe cellulitis in children, intravenous therapy is the standard of care, with home IV ceftriaxone being non-inferior to hospital IV flucloxacillin 3, 8

Why Surgical Consultation Is Mandatory

Surgical evaluation is critical because:

• Subperiosteal abscess occurs in late-acute osteomyelitis and requires ultrasound localization followed by urgent drainage 4, 1
• Septic arthritis (an orthopedic emergency) can present similarly and demands arthrocentesis and irrigation within hours to prevent cartilage destruction 1
• Necrotizing fasciitis must be excluded, as pain out of proportion to examination, crepitus, or rapidly spreading erythema mandate surgical exploration within 1-4 hours 5, 6
• Osteomyelitis with substantial bone necrosis or exposed bone requires surgical debridement as the cornerstone of therapy, particularly for MRSA infections 7, 2

Recommended Treatment Algorithm

Immediate Actions (Within 1-2 Hours)

1. Obtain surgical consultation urgently to assess for abscess, osteomyelitis, or necrotizing infection 5, 1
2. Perform bedside ultrasound of the affected leg to detect subperiosteal fluid collections, which distinguish cellulitis from abscess and guide surgical planning 4
3. Start empiric IV antibiotics immediately after obtaining blood cultures (do not delay for imaging) 5, 6:
   • First-line: IV flucloxacillin 50 mg/kg every 6 hours (covers MSSA and streptococci) 3, 2
   • Alternative (if MRSA suspected): IV vancomycin 15 mg/kg every 6-8 hours PLUS ceftriaxone 50-75 mg/kg once daily 7, 2
   • If local MRSA resistance <10%: IV clindamycin 10-13 mg/kg every 6-8 hours may be used 7

Diagnostic Workup (Within 4-6 Hours)

• Plain radiographs of the lower leg to detect cortical erosion, periosteal reaction, or gas in tissues 1, 7
• MRI with gadolinium if osteomyelitis suspected (most sensitive for bone and soft tissue involvement) 1, 7
• Laboratory markers: CBC with differential, CRP, ESR (CRP >2.0 mg/dL strongly predicts septic arthritis) 1
• Blood cultures before antibiotics (positive in ~30-50% of pediatric osteomyelitis) 2

Surgical Intervention Criteria

Proceed to urgent drainage if:

• Ultrasound or MRI confirms subperiosteal abscess or deep soft tissue collection 4, 1
• Clinical signs of necrotizing infection (crepitus, rapidly spreading necrosis, systemic toxicity) 5, 6
• No clinical improvement after 48-72 hours of appropriate IV antibiotics 2, 7
• Exposed bone or substantial bone necrosis on imaging 7

Duration of IV Therapy

• Cellulitis without abscess: 2-3 days IV until fever resolves and erythema stabilizes, then switch to oral antibiotics for total 7-10 days 3, 2
• Cellulitis with drained abscess: 3-5 days IV, then oral for total 10-14 days 6
• Osteomyelitis: Minimum 3-7 days IV (until afebrile and CRP decreasing), then oral for total 4-6 weeks 2, 7

Common Pitfalls to Avoid

• Do not discharge on oral antibiotics alone when fever and enlarging erythema are present—this risks progression to sepsis or necrotizing infection 3, 5
• Do not delay surgical consultation for prolonged antibiotic trials—abscess drainage within 24-48 hours dramatically improves outcomes 5, 6
• Do not rely on normal radiographs to exclude osteomyelitis—plain films are insensitive in the first 10-14 days, and MRI or ultrasound is required 1, 4
• Do not use oral beta-lactams for initial treatment—their bioavailability is too low for serious infections 7
• Do not assume stable vitals mean mild infection—children compensate well until sudden decompensation occurs 1, 2

Transition to Oral Therapy

Once the child is afebrile for 24-48 hours, erythema is receding, and CRP is decreasing, transition to oral antibiotics 2, 3:

• First-line: Cephalexin 25-50 mg/kg/day divided every 6-8 hours 2
• If MRSA: Clindamycin 10-13 mg/kg every 6-8 hours (if susceptible) or TMP-SMX 4 mg/kg (TMP component) twice daily 7, 2

Follow-Up and Monitoring

• Reassess clinically within 24-48 hours to confirm improvement (reduced pain, fever resolution, stable or receding erythema) 2, 6
• Repeat CRP at 3-5 days to guide duration of therapy (should decrease by ≥50%) 2, 7
• If no improvement after 4 days, re-evaluate for undiagnosed abscess (repeat ultrasound/MRI), osteomyelitis (obtain MRI), or antibiotic-resistant organisms (repeat cultures) 6, 7