Skin and soft tissue infection is the presentation most likely to lull you into a low-effort case. A red, warm, tender leg looks like a prescription and a discharge. And most of the time it is. But the simulation uses this complaint specifically because a small fraction of these patients have necrotizing fasciitis, and the candidate who treats every red limb as simple cellulitis will eventually hand in a case where the patient decompensates while they are writing a cephalexin prescription.
The skill being tested here is triage: purulent or not, systemic or not, surgical or not. Get those three sorts right and the orders follow mechanically. This guide covers the opening sequence, the branch points, the mimics that are not infection at all, and a complete order set.
Why this presentation is high-yield on CCS
• It has a true surgical emergency hiding in it. Necrotizing fasciitis is diagnosed clinically and treated in the operating room. Delay is the error the case is built to detect.
• It tests antibiotic reasoning, not antibiotic recall. Whether you cover methicillin-resistant Staphylococcus aureus depends on whether there is pus, not on habit.
• The disposition is the question. Outpatient versus admission versus operating room is the scored decision, and each path has its own order set.
• It appears in every setting. Clinic, emergency department, and as a post-operative or inpatient complication.
For the framework this spoke sits inside, see the CCS approach by chief complaint.
The first 60 seconds
Read the vitals before anything else. Fever with tachycardia and hypotension converts this from a skin case into a sepsis case, and the clock matters from that moment.
Immediate orders:
1. Vital signs
2. IV access — two large-bore lines if there is any systemic toxicity
3. Cardiac monitor and pulse oximetry, if unstable
4. Fingerstick glucose — diabetes changes the differential and the disposition
5. Mark the border of the erythema with a skin marker
Then examine, and examine carefully. The findings that change management are all physical:
• Extent and margins of erythema — measure and document
• Fluctuance — is there a drainable collection?
• Crepitus — subcutaneous gas
• Pain out of proportion to the visible findings
• Bullae, dusky or violaceous skin, frank necrosis, anesthesia over the area
• Lymphangitic streaking and regional lymphadenopathy
• Portal of entry — interdigital tinea, a puncture wound, an ulcer, an insect bite, a surgical incision
• Peripheral pulses, sensation, and the ability to bear weight
• Whether the process crosses a joint, and whether that joint moves
Labs:
• CBC with differential
• BMP
• C-reactive protein or erythrocyte sedimentation rate
• Lactate, if there is any systemic sign
• Blood cultures — two sets, before antibiotics, if the patient is febrile or toxic
• Wound or abscess culture, if there is drainable pus
• Creatine kinase, if necrotizing infection or myonecrosis is a consideration
• Hemoglobin A1c, in a newly identified diabetic
Advance the clock 15–30 minutes for stat labs — but place antibiotics and fluids first if the patient is septic. Never advance with treatment unordered.
Branch points
Branch 1: nonpurulent cellulitis, no systemic signs
Diffuse erythema with no fluctuance and normal vitals is usually streptococcal. Cover for streptococci; you do not need methicillin-resistant coverage here.
• Oral cephalexin, or dicloxacillin
• Clindamycin for a patient with significant penicillin allergy
• Elevate the affected limb
• Treat the portal of entry — topical antifungal for interdigital tinea pedis
• Analgesia, and acetaminophen for fever
• Border marked, with follow-up in 48 hours to confirm it is receding
• Discharge home with clear return precautions
Branch 2: purulent infection or abscess
A fluctuant collection is a procedure, not a prescription. Antibiotics alone will not resolve an abscess.
• Incision and drainage — this is the definitive treatment and ordering it earns credit
• Send the drained material for Gram stain and culture
• Add coverage for methicillin-resistant Staphylococcus aureus: trimethoprim-sulfamethoxazole, doxycycline, or clindamycin
• Wound packing and dressing, with a wound check in 48 hours
• Ultrasound of the soft tissue if you are unsure whether a collection is present
Branch 3: systemic toxicity — treat this as sepsis
Fever, tachycardia, hypotension, confusion, or a rising lactate moves the patient onto the sepsis pathway immediately.
• Blood cultures before antibiotics
• IV crystalloid resuscitation
• Broad empiric IV antibiotics — vancomycin for resistant staphylococci, plus a broad-spectrum agent such as piperacillin-tazobactam
• Serial lactate
• Admit; intensive care if the patient requires vasopressors
• Narrow the regimen once cultures return
Run the full escalation sequence from CCS fever and sepsis in parallel with the wound care.
Branch 4: necrotizing fasciitis — the case-defining branch
Suspect it when you see pain disproportionate to the exam, rapid progression over hours, crepitus, bullae or skin necrosis, anesthesia over the involved skin, or systemic toxicity out of keeping with a modest-looking rash.
• Surgical consultation, stat. The diagnosis is made in the operating room and the treatment is debridement. Do not delay the consult while you wait for imaging.
• Broad empiric coverage: vancomycin plus piperacillin-tazobactam, plus clindamycin for its effect on toxin production
• Aggressive IV fluid resuscitation
• Blood cultures, lactate, coagulation studies, type and crossmatch
• NPO and informed consent for operative intervention
• Transfer to intensive care
• Plain films or computed tomography may show soft tissue gas, but a negative study does not exclude the diagnosis and must not slow the operation
This is the single most important branch in the case. A candidate who orders antibiotics and admits to a medical floor has gotten the medicine partly right and the disposition fatally wrong. Place the surgical consult on the same pass as your antibiotics and fluids, not after the next clock advance.
Branch 5: the diabetic foot
An ulcer in a diabetic foot is a different problem with a different workup.
• Probe the ulcer — if it probes to bone, assume osteomyelitis
• Plain radiograph first; magnetic resonance imaging if films are unrevealing and osteomyelitis is still suspected
• Vascular assessment — pulses, ankle-brachial index
• Broad-spectrum coverage including anaerobes for a deep or chronic infection
• Surgical or podiatric consultation for debridement
• Offloading, wound care, glycemic control
• Bone biopsy for culture if osteomyelitis is confirmed
For the inpatient glycemic management that runs alongside, see CCS diabetic emergencies.
Branch 6: exposure-specific infections
The history of exposure changes the antibiotic.
• Salt water or shellfish exposure, especially with liver disease — consider Vibrio vulnificus; doxycycline plus a third-generation cephalosporin, and surgical evaluation
• Fresh water exposure — consider Aeromonas
• Dog or cat bite — Pasteurella; amoxicillin-clavulanate. Cat bites are puncture wounds and get infected more often
• Human bite — Eikenella; amoxicillin-clavulanate, and examine for joint or tendon involvement
• Any wound — check and update tetanus status; consider rabies prophylaxis for the appropriate animal exposure
Don't-miss diagnoses and mimics
1. Necrotizing fasciitis — pain out of proportion, rapid progression, systemic toxicity. Surgery, now.
2. Septic arthritis — if the overlying joint is hot and will not move, arthrocentesis before you commit to a skin diagnosis. See CCS joint pain and septic arthritis.
3. Deep vein thrombosis — a unilateral swollen, tender calf is on both differentials. Order a venous duplex ultrasound when the picture is ambiguous; see CCS deep vein thrombosis and anticoagulation.
4. Osteomyelitis — chronic ulcer, exposed bone, or failure to improve on appropriate antibiotics.
5. Stasis dermatitis — bilateral, chronic, no fever. Cellulitis is almost never bilateral. Treating bilateral chronic leg erythema with antibiotics is a classic unnecessary action.
6. Gout or pseudogout — monoarticular, exquisitely tender, may look infected. Arthrocentesis distinguishes them.
7. Toxic shock syndrome — diffuse erythroderma, hypotension, multiorgan involvement.
8. Periorbital versus orbital cellulitis — pain with eye movement, proptosis, or restricted motility means orbital involvement. Order computed tomography of the orbits, admit for IV antibiotics, and consult ophthalmology.
9. Erythema migrans — an expanding targetoid lesion after outdoor exposure is Lyme disease, treated with doxycycline.
Complete order set: soft tissue infection in the emergency department
Immediate:
• Vital signs
• IV access
• Fingerstick glucose
• Mark erythema border
• Cardiac monitor and pulse oximetry, if unstable
• IV fluids, if febrile or hypotensive
Examination:
• Focused skin and soft tissue exam — fluctuance, crepitus, bullae, necrosis
• Neurovascular exam of the limb
• Joint range of motion
• Full skin survey for a portal of entry
Labs:
• CBC with differential
• BMP
• C-reactive protein
• Lactate
• Blood cultures, two sets, before antibiotics
• Wound or abscess culture and Gram stain
• Creatine kinase
• Coagulation studies and type and crossmatch, if operative
• Hemoglobin A1c, where relevant
Imaging:
• Soft tissue ultrasound — to find a drainable collection
• Plain radiograph — soft tissue gas, foreign body, bony involvement
• Computed tomography or magnetic resonance imaging — deep space infection or osteomyelitis, but never as a reason to delay surgery
• Venous duplex ultrasound — if thrombosis is on the differential
Procedures and treatment:
• Incision and drainage for any abscess
• Surgical debridement for necrotizing infection
• Oral cephalexin or dicloxacillin — simple nonpurulent cellulitis
• Trimethoprim-sulfamethoxazole, doxycycline, or clindamycin — purulent infection
• IV vancomycin plus piperacillin-tazobactam — systemic toxicity or necrotizing infection
• Clindamycin added for toxin suppression in necrotizing infection
• Limb elevation, wound care, dressing changes
• Analgesia and antipyretics
• Tetanus immunization update
• Topical antifungal for tinea pedis
Consults:
• General surgery — necrotizing infection, deep abscess, diabetic foot debridement
• Orthopedics — septic joint or osteomyelitis
• Ophthalmology — orbital cellulitis
• Infectious disease — resistant organism or unusual exposure
Disposition:
• Operating room, then intensive care — necrotizing fasciitis
• Intensive care — septic shock requiring vasopressors
• Admit to floor with IV antibiotics — systemic signs, failed outpatient therapy, immunocompromise, rapidly advancing margins, inability to take oral medication
• Discharge home on oral antibiotics — well-appearing, afebrile, reliable follow-up, marked border
Follow-up and preventive:
• Wound check or clinic follow-up in 48 hours
• Diabetic foot care education and annual foot examination
• Treat and prevent recurrent tinea pedis
• Compression and skin care for chronic edema, to prevent recurrence
• Smoking cessation counseling
• Return precautions: fever, spreading redness beyond the mark, increasing pain, drainage, numbness
Drill it
The pattern to internalize is small: look for pus, look for systemic signs, and look for pain that does not fit. Each one sends you down a different path, and the order sets above are short enough to memorize. Run these cases end to end on CCS cases and practice getting the opening block in quickly on SpeedOrder.
Related guides:
• CCS Fever & Sepsis: Rapid Workup, Orders & Escalation
• CCS Joint Pain & Septic Arthritis
