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id.cellulitis.core.v1PRODUCTION
id.cellulitis.core.v1

Cellulitis & erysipelas

infectious_diseaseacuteadult
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0 / 11
Care setting:

Encounter flow

12/12 authored

Canonical 12-phase frame with authored status for this dossier.

Current phase

Frame

Detailed

Non-purulent vs purulent cellulitis (IDSA 2014 SSTI Stevens — distinct empiric pathways); exclude necrotizing fasciitis (separate engine) and erysipelas variant (NICE 2019 NG141)

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Actions
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Advance rule
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scope confirmed

Patient inputs (15)

Eron II/III/IV classification; informs IV vs PO and admission threshold (Eron 2003; CREST 2005 — fever drives Eron class upgrade)

Tachycardia → SIRS / qSOFA element (SSC 2021; IDSA 2014 SSTI Stevens — systemic toxicity marker)

Purulent SSTI → MRSA coverage (IDSA 2014)

Drives empiric MRSA coverage (IDSA 2014 SSTI Stevens — purulent SSTI requires anti-MRSA empiric therapy)

Polymicrobial coverage threshold; healing trajectory (IDSA 2014 SSTI Stevens; IDSA 2012 diabetic foot — broader empirics)

Broader empirics + lower admission threshold (IDSA 2014 SSTI Stevens — immunocompromised host requires Eron class upgrade; NICE 2019 NG141)

SIRS criterion + severity tracking (IDSA 2014 SSTI Stevens — baseline CBC for systemic assessment)

Hypotension upgrades to Eron IV / sepsis pathway (Eron 2003 class IV; SSC 2021 — septic shock definition)

Necrotizing fasciitis red flag — STAT surgical eval (IDSA 2014 SSTI Stevens — cardinal sign of necrotizing infection)

Necrotizing fasciitis or gas gangrene red flag (IDSA 2014 SSTI Stevens — crepitus indicates gas-forming organisms)

Cefazolin / vancomycin renal dosing (IDSA 2014 SSTI Stevens — dose adjustment; IDSA 2020 vancomycin consensus — AUC-based dosing)

Rule out DVT mimic; abscess / fluid collection (NICE 2019 NG141 — unilateral leg swelling differential; IDSA 2014 SSTI Stevens — bedside US for abscess)

Modifiable risk factor for recurrence (NICE 2019 NG141); PATCH II prophylaxis candidacy (Thomas NEJM 2013 PATCH II)

Trend for response to therapy (NICE 2019 NG141 — serial CRP guides IV-to-PO switch and duration)

Sepsis bundle when SIRS + skin source (SSC 2021 — lactate-guided resuscitation in SSTI sepsis)

* = hard-required. Engine cannot meaningfully run until these are filled.

Severity triggers (9)

9 need judgement
  • informationallife_threateningnecrotising_features
    Pain out of proportion, crepitus, bullae, rapid spread, systemic toxicity, "dishwater" drainage, OR LRINEC ≥6 (IDSA 2014 SSTI Stevens)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseveresepsis_with_skin_source
    qSOFA ≥2 OR SIRS positive + skin/soft tissue source (SSC 2021)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseverecellulitis_progressing_on_appropriate_antibiotics
    Failure to improve at 48-72 h after appropriate empiric therapy — extension of erythema border / new systemic toxicity / new abscess on US (IDSA 2014 SSTI Stevens)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalsevereeron_class_3_or_4_at_presentation
    Eron class 3 (significant systemic toxicity OR unstable comorbidity) or class 4 (sepsis / NF features) at initial assessment (Eron 2003; CREST 2005)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseverecellulitis_in_immunocompromised_host
    Neutropenic (ANC < 500) / transplant recipient / biologic agent / advanced HIV / chemotherapy host with cellulitis (IDSA 2014 SSTI Stevens; IDSA 2024 febrile neutropenia)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmoderatefluctuant_abscess
    Fluctuant collection on exam or US (IDSA 2014 SSTI Stevens)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmoderatemrsa_risk_factors
    Prior MRSA colonisation, IVDU, recent hospitalisation, household MRSA, persistent purulence (IDSA 2014 SSTI Stevens)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmoderatediabetic_foot_or_water_animal_exposure
    Diabetic foot infection, fresh or salt water exposure, animal/human bite (IDSA 2014 SSTI Stevens; IDSA 2012 diabetic foot)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmildrecurrent_cellulitis
    ≥2 episodes/year of cellulitis in same limb (Thomas NEJM 2013 PATCH II)
    Trigger could not be auto-evaluated — needs clinician judgement.

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Recommended regimen

Non-purulent cellulitis (outpatient PO)
axis: cellulitis_empiric_outpatient
Selected axis "Non-purulent cellulitis (outpatient PO)" by default fallback (first axis)
  • cephalexin
    first line
    1st_gen_cephalosporin
    triggers: non_purulent, no_mrsa_risk
    IDSA 2014 strong recommendation for non-purulent SSTI; covers strep + MSSA
    rxcui 2231
  • dicloxacillin
    first line
    antistaph_penicillin
    triggers: non_purulent
    IDSA 2014 alternative; flucloxacillin first-line in UK NICE NG141
    rxcui 3356
  • clindamycin
    contraindication substitute
    lincosamide
    triggers: penicillin_severe_allergy
    IDSA 2014 SSTI Stevens — beta-lactam allergy backup; variable MRSA coverage (check local susceptibility)
    rxcui 2582

outpatient playbook — drug actions (5)

  1. 1. cephalexin (non-purulent)
    500 mg PO • PO • QID × 5-7 d (Phoenix G NEJM 2023 STOP trial)
    trigger: Eron I, non-purulent, no MRSA risk (Eron 2003; IDSA 2014 SSTI Stevens)
    IDSA 2014 SSTI Stevens — covers strep + MSSA
  2. 2. dicloxacillin alternative
    500 mg PO • PO • QID × 5-7 d (Phoenix G NEJM 2023 STOP trial)
    trigger: Non-purulent alternative (IDSA 2014 SSTI Stevens)
    IDSA 2014 SSTI Stevens / NICE 2019 NG141 — flucloxacillin in UK
  3. 3. TMP-SMX (purulent or MRSA risk)
    1-2 DS PO • PO • BID × 5-7 d (Phoenix G NEJM 2023 STOP trial)
    trigger: Purulent cellulitis or MRSA risk factor (IDSA 2014 SSTI Stevens)
    IDSA 2014 SSTI Stevens — covers CA-MRSA
  4. 4. doxycycline alternative
    100 mg PO • PO • BID × 5-7 d (Phoenix G NEJM 2023 STOP trial)
    trigger: TMP-SMX intolerant + MRSA risk (IDSA 2014 SSTI Stevens)
    IDSA 2014 SSTI Stevens alternative
  5. 5. clindamycin
    300-450 mg PO • PO • QID × 5-7 d (Phoenix G NEJM 2023 STOP trial)
    trigger: Severe penicillin allergy (IDSA 2014 SSTI Stevens)
    IDSA 2014 SSTI Stevens — beta-lactam allergy backup; counsel C difficile risk (IDSA 2014 SSTI Stevens)

Auto-drafted A&P note

outpatient

Subjective

- Possible entry pathways: Unilateral lower-extremity erythema, warmth, swelling, tenderness (IDSA 2014 SSTI Stevens — classic presentation; NICE 2019 NG141); Sharply demarcated facial erythema (erysipelas) (NICE 2019 NG141 — raised, well-defined border; IDSA 2014 SSTI Stevens); Leukocytosis + clinical skin signs (IDSA 2014 SSTI Stevens — systemic inflammatory response).

Objective

- No vitals, labs, or imaging entered for this encounter.

Assessment

**Cellulitis & erysipelas** (id.cellulitis.core.v1).
Phenotype framing: DVT, stasis dermatitis, contact dermatitis, gout, septic arthritis, necrotizing fasciitis, lymphedema, erysipeloid, erythema migrans (NICE 2019 NG141 — common mimics of cellulitis; IDSA 2014 SSTI Stevens — misdiagnosis rate 30%)
Scope: Non-purulent vs purulent cellulitis (IDSA 2014 SSTI Stevens — distinct empiric pathways); exclude necrotizing fasciitis (separate engine) and erysipelas variant (NICE 2019 NG141)

No severity triggers fired against current inputs.

Plan

Regimen axis: **Non-purulent cellulitis (outpatient PO)**.
1. cephalexin (1st_gen_cephalosporin, first line) — IDSA 2014 strong recommendation for non-purulent SSTI; covers strep + MSSA
2. dicloxacillin (antistaph_penicillin, first line) — IDSA 2014 alternative; flucloxacillin first-line in UK NICE NG141
3. clindamycin (lincosamide, contraindication substitute) — IDSA 2014 SSTI Stevens — beta-lactam allergy backup; variable MRSA coverage (check local susceptibility)

Setting playbook (outpatient) — Manage Eron I-II non-severe cellulitis with PO antibiotics, recheck at 48-72 h, address modifiable risk factors (Eron 2003; CREST 2005; NICE 2019 NG141)
4. cephalexin (non-purulent) 500 mg PO PO QID × 5-7 d (Phoenix G NEJM 2023 STOP trial) — Eron I, non-purulent, no MRSA risk (Eron 2003; IDSA 2014 SSTI Stevens) (IDSA 2014 SSTI Stevens — covers strep + MSSA)
5. dicloxacillin alternative 500 mg PO PO QID × 5-7 d (Phoenix G NEJM 2023 STOP trial) — Non-purulent alternative (IDSA 2014 SSTI Stevens) (IDSA 2014 SSTI Stevens / NICE 2019 NG141 — flucloxacillin in UK)
6. TMP-SMX (purulent or MRSA risk) 1-2 DS PO PO BID × 5-7 d (Phoenix G NEJM 2023 STOP trial) — Purulent cellulitis or MRSA risk factor (IDSA 2014 SSTI Stevens) (IDSA 2014 SSTI Stevens — covers CA-MRSA)
7. doxycycline alternative 100 mg PO PO BID × 5-7 d (Phoenix G NEJM 2023 STOP trial) — TMP-SMX intolerant + MRSA risk (IDSA 2014 SSTI Stevens) (IDSA 2014 SSTI Stevens alternative)
8. clindamycin 300-450 mg PO PO QID × 5-7 d (Phoenix G NEJM 2023 STOP trial) — Severe penicillin allergy (IDSA 2014 SSTI Stevens) (IDSA 2014 SSTI Stevens — beta-lactam allergy backup; counsel C difficile risk (IDSA 2014 SSTI Stevens))

Non-pharmacologic actions:
- Elevate limb (NICE 2019 NG141; CREST 2005)
- Treat tinea pedis (topical antifungal × 4 wk) (NICE 2019 NG141 — modifiable recurrence risk factor)
- Compression for chronic edema once acute resolves (NICE 2019 NG141)
- Mark border; recheck 48-72 h in clinic or telemedicine (CREST 2005; NICE 2019 NG141)
- Wound care education (IDSA 2014 SSTI Stevens)

AVOID / contraindication checks:
- Penicillin anaphylaxis block cephalexin (IDSA 2014 SSTI Stevens — cross reactivity risk)
- Clindamycin c diff counsel (IDSA 2014 SSTI Stevens — C difficile association)

Monitoring

Regimen monitoring:
- border tracing at 48-72h (CREST 2005; NICE 2019 NG141)
- symptom review day 3 and day 7 (IDSA 2014 SSTI Stevens)

Setting (outpatient) monitoring:
- Border tracing 48-72 h (CREST 2005; NICE 2019 NG141)
- Symptom review days 3 + 7 (IDSA 2014 SSTI Stevens)
- Return precautions for fever, expanding erythema, systemic features (NICE 2019 NG141)

Follow-up plan: Treat tinea pedis / lymphedema / venous insufficiency (NICE 2019 NG141 — modifiable risk factors); PATCH II prophylactic penicillin V if ≥2 episodes/year (Thomas NEJM 2013 PATCH II); counsel on early re-presentation (NICE 2019 NG141)
- Close-out criterion: recurrence-prevention plan documented

Monitoring phase: Border tracing 24-48h (CREST 2005; NICE 2019 NG141); CRP / WBC trend (IDSA 2014 SSTI Stevens); transition IV→PO when afebrile + improving 48h (NICE 2019 NG141 — IV-to-PO switch criteria)

Disposition

Current setting: outpatient — Manage Eron I-II non-severe cellulitis with PO antibiotics, recheck at 48-72 h, address modifiable risk factors (Eron 2003; CREST 2005; NICE 2019 NG141)

Disposition criteria:
- Continue PO antibiotics if improving (IDSA 2014 SSTI Stevens)
- Step up to IV / inpatient if Eron III or non-response (Eron 2003; NICE 2019 NG141)

Escalation triggers (move to higher acuity):
- No improvement / worsening at 48-72 h → ED for IV antibiotics + imaging (IDSA 2014 SSTI Stevens; NICE 2019 NG141)
- Systemic features (fever, tachycardia) → ED (Eron 2003 class III-IV)
- Necrotising features → emergent ED + surgery (IDSA 2014 SSTI Stevens)

Earlier-Return Triggers

Return-precaution thresholds (watch for):
- [LIFE_THREATENING] Pain out of proportion, crepitus, bullae, rapid spread, systemic toxicity, "dishwater" drainage, OR LRINEC ≥6 (IDSA 2014 SSTI Stevens)
- [SEVERE] qSOFA ≥2 OR SIRS positive + skin/soft tissue source (SSC 2021)
- [SEVERE] Failure to improve at 48-72 h after appropriate empiric therapy — extension of erythema border / new systemic toxicity / new abscess on US (IDSA 2014 SSTI Stevens)

Citations

- IDSA 2014 SSTI Guideline (Stevens et al, CID) + NICE NG141 (2019, updated 2024) + Eron 2003 classification + CREST 2005 cellulitis guidelines + Thomas NEJM 2013 PATCH II + Phoenix G NEJM 2023 STOP duration trial [PMID:24973422](https://pubmed.ncbi.nlm.nih.gov/24973422/)
- Cited evidence (PMID 23635049) [PMID:23635049](https://pubmed.ncbi.nlm.nih.gov/23635049/)
- Cited evidence (PMID 15241098) [PMID:15241098](https://pubmed.ncbi.nlm.nih.gov/15241098/)
- Cited evidence (PMID 22619242) [PMID:22619242](https://pubmed.ncbi.nlm.nih.gov/22619242/)

Last reconciled with current guidelines: 2026-05-22.
References
  • IDSA 2014 SSTI Guideline (Stevens et al, CID) + NICE NG141 (2019, updated 2024) + Eron 2003 classification + CREST 2005 cellulitis guidelines + Thomas NEJM 2013 PATCH II + Phoenix G NEJM 2023 STOP duration trial — PMID:24973422
  • Cited evidence (PMID 23635049) — PMID:23635049
  • Cited evidence (PMID 15241098) — PMID:15241098
  • Cited evidence (PMID 22619242) — PMID:22619242