Why use it

Provides objective risk stratification for CDI treatment failure beyond simple severity classification. Helps guide antibiotic selection (fidaxomicin vs. vancomycin vs. metronidazole) and intensity of monitoring. Identifies high-risk patients who may benefit from additional interventions such as bezlotoxumab (monoclonal antibody against toxin B), fecal microbiota transplant planning, or surgical consultation.

About

The ATLAS score is a validated clinical scoring system developed to predict failure of standard antibiotic therapy (vancomycin or metronidazole) in patients with Clostridioides difficile infection (CDI). It uses five variables — Age, Treatment with systemic antibiotics, Leukocyte count, Albumin, and Serum creatinine — to generate a score from 0 to 10. Higher scores are associated with greater likelihood of treatment failure, recurrence, and adverse outcomes. The ATLAS score was originally developed to identify patients who might benefit from fidaxomicin over vancomycin in clinical practice, as fidaxomicin has demonstrated superior sustained cure rates in high-ATLAS score patients.

When to use

Patients with newly confirmed CDI at time of diagnosis and antibiotic selection
Guiding choice between fidaxomicin and vancomycin (higher ATLAS score → favor fidaxomicin)
Identifying patients at high risk for recurrence who may benefit from bezlotoxumab
Risk stratification in recurrent CDI cases
Clinical research and outcomes studies for CDI

Formula

ATLAS Score = Sum of 5 domains (0–2 points each): A = Age: ≤ 60 years: 0 61–75 years: +1 ≥ 76 years: +2 T = Treatment with concurrent systemic antibiotics (non-CDI): No: 0 Yes: +2 L = Leukocyte count (×10³/µL): ≤ 16: 0 16.1–25: +1 > 25: +2 A = Albumin (g/dL): > 3.5: 0 2.6–3.5: +1 ≤ 2.5: +2 S = Serum creatinine (mg/dL): ≤ 1.0: 0 1.1–1.5: +1 > 1.5: +2 Total: 0–10 Low (0–3): High cure probability Intermediate (4–7): Moderate cure probability High (8–10): Lower cure probability — escalate therapy

Pearls & pitfalls

ATLAS specifically predicts TREATMENT FAILURE (not initial severity) — it complements the IDSA/SHEA severity classification.
Fidaxomicin has demonstrated superior sustained cure rates (reduced recurrence) in patients with ATLAS score ≥ 6 in post-hoc analyses.
Concurrent systemic antibiotics (for another infection) are weighted most heavily (+2) because they perpetuate gut dysbiosis and impair CDI resolution.
Albumin < 2.5 g/dL scores the highest (+2) for the albumin domain — reflecting poor nutritional reserve and severe systemic illness.
Bezlotoxumab (Zinplava) reduces CDI recurrence by ~40% in high-risk patients — ATLAS helps identify who might most benefit.
Fecal microbiota transplant (FMT) has 85–90% cure rates in recurrent CDI and should be considered after 2+ recurrences regardless of ATLAS score.
ATLAS is complementary to — not a replacement for — the IDSA/SHEA CDI severity criteria (mild/moderate/severe/fulminant).
Proton pump inhibitors, age ≥ 65, and immunocompromised state are risk factors for recurrence not captured by ATLAS.

Next steps

ATLAS 0–3 (Low risk): Cure rate ~90% with standard therapy. Metronidazole or oral vancomycin are appropriate first-line options. ATLAS 4–7 (Intermediate risk): Cure rate ~75–85%. Prefer oral vancomycin or fidaxomicin. Consider bezlotoxumab if recurrent CDI. ATLAS 8–10 (High risk): Cure rate < 70%. Fidaxomicin preferred; consider bezlotoxumab to reduce recurrence; surgical consultation if severe colitis; monitor closely for colectomy indications.

Evidence

Miller MA et al. (Clin Infect Dis 2013) derived the ATLAS score from 185 CDI patients. Validated in the MODIFY II trial of bezlotoxumab. Corbet C et al. (Open Forum Infect Dis 2019) validated ATLAS in a multicenter cohort. ATLAS ≥ 6 identifies patients with significantly higher recurrence rates where fidaxomicin provides meaningful benefit over vancomycin (post-hoc analysis of CLARITY trial).

References

Miller MA et al. Clinical management and burden of Clostridioides difficile infection: a multicenter study in Canada. Clin Infect Dis. 2013;57(2):170-180. — link
Cornely OA et al. Fidaxomicin versus vancomycin for infection with Clostridioides difficile in Europe, Canada, and the USA: a double-blind, non-inferiority, randomised controlled trial. Lancet Infect Dis. 2012;12(4):281-289. — link
Gerding DN et al. Bezlotoxumab for prevention of recurrent Clostridioides difficile infection. N Engl J Med. 2017;376(4):305-317. — link

ATLAS Score for Clostridioides difficile Infection

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