We included 8 predictor variables in the SP model (sex, age ≥65 years, failure of outpatient antibiotics, fever, hyponatremia, intensive care unit admission, PSI risk class ≥IV, and use of empiric broad-spectrum antibiotics), and 4 predictor variables in the LP model (recent travel, fever, diarrhea, and hyponatremia). To prevent model overfitting, we limited the number of predictor variables to approximately 10 degrees of freedom per outcome (positive UAT). Next, we constructed separate multivariable logistic regression models to identify the factors independently associated with a positive SP or LP UAT result. Using simple logistic regression, we also assessed the association of potential predictors of SP and LP pneumonia, as identified in a literature review ( Supplementary Table 3), with actual SP and LP UAT results. Using these contingency tables, sensitivity and specificity for the recommended testing indications were calculated. Then, separate 2-by-2 contingency tables were developed for SP and LP, with the exposure variable being whether testing indications were met (UAT recommended vs not recommended) and the outcome variable being the UAT result (positive vs negative). Simple logistic regression was used to calculate the odds ratio (OR) for each indication (odds of the indication being present in patients with a positive UAT compared to those with a negative UAT). First, we compared the prevalence of each of the IDSA/ATS indications for SP and LP urinary antigen testing between patients who had positive and negative UAT results. Patients with any of the Legionella criteria in Table 1 were classified as meeting LP UAT testing indications. Patients with any of the pneumococcal criteria in Table 1 were classified as meeting SP UAT testing indications. We classified each patient as meeting or not meeting IDSA/ATS UAT testing indications for SP and, separately, for LP. Methods for viral testing and procalcitonin measurement have been previously described. In supplemental analyses, results for SP and LP UATs were described in the context of viral testing and procalcitonin results. Hence, variables such as viral detection by polymerase chain reaction and procalcitonin concentration were not evaluated in the main analysis. To simulate the clinical environment in which UATs are typically used, we limited the predictor variables in our analysis to the clinical data that are routinely available within the first few hours after a CAP diagnosis. Empiric use of broad-spectrum antibiotics was defined as administration of at least 1 of the following antibiotics on the date of admission or the next calendar day: an antipseudomonal beta-lactam, aminoglycoside, carbapenem, vancomycin, linezolid, aztreonam, or daptomycin. We evaluated 2 definitions for severe CAP: (1) ≥3 IDSA/ATS minor criteria present at the time of hospital arrival and (2) Pneumonia Severity Index (PSI) risk class IV or V. These variables included age ≥65 years, fever, nausea, diarrhea, confusion, headache, hyponatremia (serum sodium < 130 mmol/L), severe CAP, and empiric use of broad-spectrum antibiotics. In addition to recommendations in the IDSA/ATS CAP guidelines for UAT indications, we also evaluated other clinical characteristics that were identified in prior studies as potentially predictive of pneumococcal and Legionella CAP ( Supplementary Table 3). Additionally, we evaluated the association of clinical characteristics not included in the current guidelines with SP and LP UAT results to identify additional risk factors that may improve future guidelines.Ībbreviations: ICU, intensive care unit LP, Legionella pneumophila SP, Streptococcus pneumoniae UAT, urinary antigen test. The objective of this study was to use a large, prospective cohort of adult CAP patients with universal urinary antigen testing to evaluate the accuracy of the risk factor–based approach described in the 2007 IDSA/ATS CAP guidelines for identifying which patients to test with UATs. Prior studies examining risk factors for positive SP and LP UATs have been retrospective and limited by indication biases, with UATs being ordered at the discretion of the treating clinician or local practice. These recommendations were based on expert opinions and have not been extensively evaluated since publication.
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These guidelines recommend SP and LP urinary antigen tests (UAT) for hospitalized adults with any of several clinical characteristics (risk factors) associated with S. In 2007, the Infectious Disease Society of America and the American Thoracic Society (IDSA/ATS) jointly published management guidelines for community-acquired pneumonia (CAP) in adults, which included recommendations regarding which patients should undergo urinary antigen testing for Streptococcus pneumoniae (SP) or Legionella pneumophila (LP).
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Pneumonia is the leading cause of hospitalization and death due to infection in the United States.
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( See the Editorial Commentary by Murdoch on pages 2034–5.)