Evaluation of the Winthrop-University Hospital criteria to identify Legionella pneumonia

Study objective: To measure the ability of a set of clinical parameters, th e Winthrop-University Hospital (WUH) criteria, to identify, Legionella pneu monia while discriminating against bacteremic pneumococcal pneumonia at the time of hospitalization for community-acquired pneumonia (CAP). Design: Retrospective case-control study. Setting: An urban county, hospital and a tertiary-care Veterans Affairs hos pital. Patients: Thirty-seven patients with Legionella pneumonia (diagnosed by a p ositive result of a urinary Legionella antigen test) and 31 patients with b acteremic pneumococcal pneumonia. A subgroup of patients with all required laboratory criteria were studied further. Results: The WUH criteria correctly identified 29 of 37 patients with Legio nella pneumonia (sensitivity, 78%; 95% confidence interval [CI], 61 to 90%) , while successfully excluding legionellosis in 20 of 31 patients with bact eremic pneumococcal pneumonia (specificity, 65%; 95% CI, 45 to 80%). The po sitive and negative predictive values, adjusted for a relative prevalence o f 1:3 between Legionella and Streptococcus pneumoniae bacteremia, were 42% (95% CI, 25 to 61%) and 90% (95% CI, 74 to 97%), respectively. In the subgr oup analysis, the WUH criteria were successful in identifying 20 of 23 pati ents with Legionella pneumonia (sensitivity, 87%; 95% CI, 65 to 97%), while excluding legionellosis in 9 of 18 patients with bacteremic pneumococcal p neumonia (specificity, 50%; 95% CI, 27 to 73%). The adjusted positive and n egative predictive values for a 1:3 relative prevalence were 37% (95% CI, 2 0 to 59%) and 92% (95% CI, 62 to 98%), respectively. The predictive values were changed in the directions expected for an increased relative prevalenc e of 1:1. The areas under the receiver operating characteristic curves were 0.72 +/- 0.06 for the entire study group and 0.68 +/- 0.09 for the subgrou p. Conclusions: Although the WUH criteria discriminated fairly well between ca ses (mean +/- SE) and control subjects, the sensitivity is not high enough to exclude legionellosis confidently. These results suggest that empiric th erapy for Legionella pneumonia should be included in the initial antibiotic regimen for hospitalized patients with CAP.