Recommended indications for Streptococcus pneumoniae and Legionella pneumophila antigen testing in the 2007 joint guidelines issued by the Infectious Disease Society of America and the American Thoracic Society (IDSA/ATS) for community-acquired pneumonia (CAP) have poor sensitivity and specificity for identifying patients who should undergo testing for these pathogens, according to findings published in Clinical Infectious Diseases.

The guidelines recommend that S pneumoniae and L pneumophila urinary antigen tests be performed in hospitalized adults when any 1 of several clinical characteristics associated with S pneumoniae or L pneumophila infection are present. However, these recommendations are derived from expert opinion and have not been thoroughly evaluated since they were published a decade ago. In addition, most studies that have evaluated risk factors for positive S pneumoniae and L pneumophila urinary antigen tests have been retrospective and limited by indication bias.

Researchers conducted a cross-sectional study using data prospectively collected as part of the multicenter Etiology of Pneumonia in the Community study to evaluate the accuracy of the risk-factor-based approach described in the IDSA/ATS guidelines. The cohort included 1941 patients with CAP, of whom 1184 (61.0%) had ≥1 IDSA/ATS indication for S pneumoniae urine antigen testing. A total of 81 (4.2%) patients had a positive S pneumoniae urinary antigen test, and 32 (1.6%) had a positive L pneumophila urinary antigen test. The presence of ≥1 IDSA/ATS indication had a 61% (95% CI, 49%-71%) sensitivity and 39% (95% CI, 37%-41%) specificity for S pneumoniae and a 63% (95% CI, 44%-79%) sensitivity and 35% (95% CI, 33%-37%) specificity for L pneumophila.

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“A consideration for future CAP guidelines may be to abandon the risk-factor-based approach for testing indications in favor of other approaches, such as evaluating which patient types and clinical scenarios would benefit most from a microbiological diagnosis,” the researchers concluded.

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Bellew S, Grijalva CG, Williams DJ, et al. Pneumococcal and legionella urinary antigen tests in community-acquired pneumonia: prospective evaluation of indications for testing [published online September 28, 2018]. Clin Infect Dis. doi: 10.1093/cid/ciy826