Legionella Predictor

Legionella Predictor: Winthrop-University model. Estimates pre-test probability of Legionella pneumonia based on clinical and laboratory findings.

Pre-Test Probability markers

Testing Referral status

Low probability (0/6)

Legionella is unlikely. Consider standard CAP pathogens.

Guidelines & Evidence

Clinical Details

Section 1

When to Use

Evaluation of patients with CAP, particularly with atypical features

Screening during Legionella outbreaks or in patients with travel exposure

Deciding which CAP patients require Legionella-specific testing (Urinary Ag/PCR)

Section 2

Formula & Logic

Positive Criteria (1 pt each)

Temperature > 39°C (102.2°F)

Dry cough (non-productive)

Hyponatremia (Sodium < 133 mEq/L)

LDH > 2x upper limit of normal

Hypophosphatemia (PO4 < 2.4 mg/dL)

CK > 2x upper limit of normal

Interpretation

0–2 points	Low pre-test probability. Legionella unlikely.
3–4 points	Moderate probability. Consider testing if clinically suspicious.
≥ 5 points	High probability. Direct Legionella testing and empiric macrolide/quinolone therapy indicated.

Section 3

Evidence Appraisal

Validation

Winthrop-University Hospital's clinical diagnostic model for Legionella pneumonia.

Cunha BA et al. • Expert Rev Anti Infect Ther.. 2008;6(6):857-69. Clinical model showing high NPV for Legionella diagnosis.

Last Comprehensive Review: 2026

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