Pneumococcal and Legionella Urinary Antigen Tests in Community-acquired Pneumonia: Prospective Evaluation of Indications for Testing

Abstract

Background Adult, community-acquired pneumonia (CAP) guidelines from the Infectious Diseases Society of America (IDSA) and American Thoracic Society (ATS) include indications for urinary antigen tests (UATs) for Streptococcus pneumoniae (SP) and Legionella pneumophila (LP). These recommendations were based on expert opinions and have not been rigorously evaluated. Methods We used data from a multicenter, prospective, surveillance study of adults hospitalized with CAP to evaluate the sensitivity and specificity of the IDSA/ATS UAT indications for identifying patients who test positive. SP and LP UATs were completed on all included patients. Separate analyses were completed for SP and LP, using 2-by-2 contingency tables, comparing the IDSA/ATS indications (UAT recommended vs not recommended) and UAT results (positive vs negative). Additionally, logistic regression was used to evaluate the association of each individual criterion in the IDSA/ATS indications with positive UAT results. Results Among 1941 patients, UATs were positive for SP in 81 (4.2%) and for LP in 32 (1.6%). IDSA/ATS indications had 61% sensitivity (95% confidence interval [CI] 49–71%) and 39% specificity (95% CI 37–41%) for SP, and 63% sensitivity (95% CI 44–79%) and 35% specificity (95% CI 33–37%) for LP. No clinical characteristics were strongly associated with positive SP UATs, while features associated with positive LP UATs were hyponatremia, fever, diarrhea, and recent travel. Conclusions Recommended indications for SP and LP urinary antigen testing in the IDSA/ATS CAP guidelines have poor sensitivity and specificity for identifying patients with positive tests; future CAP guidelines should consider other strategies for determining which patients should undergo urinary antigen testing.

Diagnosis of severe respiratory infections in immunocompromised patients

“…Endotracheal aspirates are more likely to recover the causative organism than expectorated sputum, and organisms recovered immediately after intubation is unlikely to reflect mere colonization; in patients with malignancies and ARF, a randomized-controlled trial reported that a strategy with non-invasive testing only (including sputum sampling) was not inferior to FOB/BAL [5]. In patients admitted for CAP, urine antigen detection was 61% sensitive and 39% specific for S. pneumoniae, and corresponding values for L. pneumophila were 63% and 35% [34]. Blood cultures also have low yields of 5-14% in patients admitted for CAP [5,35], although higher yields have been reported when the pulmonary involvement was severe.…”

Urinary antigen testing for pneumococcal pneumonia: is there evidence to make its use uncommon in clinical practice?

“…Other authors have found similar rates of positive test prevalence: between 5.2% and 8.8% in ward-based patients and 15% of those requiring intensive care [18,23,24]. The low rate of positive UAT results in over 90% of tests yielding negative results [18,22,23] and these do not contribute to clinical management as the low sensitivity of UAT means a negative test result cannot exclude infection with S. pneumoniae.…”

“…A recent large prospective study found that patients who met IDSA/ATS guidelines for pneumococcal UAT infrequently had a positive result on testing (a positive test prevalence of 4.2%) [22], demonstrating that current testing indications have poor sensitivity and specificity in identifying patients with positive pneumococcal urinary antigen. Other authors have found similar rates of positive test prevalence: between 5.2% and 8.8% in ward-based patients and 15% of those requiring intensive care [18,23,24].…”

Clinical Presentation of Community-Acquired Legionella Pneumonia Identified by Universal Testing in an Endemic Area

“…Current guidelines do not recommend routine Legionella testing since empirical treatment regimens for pneumonia generally include antibiotics with anti-Legionella activity [11], and testing in low-risk settings may not be cost-effective [18]. In regions that are endemic for Legionella, however, systematic testing identifies cases that would otherwise remain undetected [12,14,19], facilitates targeted antibiotic therapy, and serves a public health function as surveillance for potential outbreaks. Rapid, accessible microbiologic methods are more sensitive and specific than any scoring algorithm and may be easier to use as a screening method than a complex score requiring multiple tests not typically sent on non-critically ill pneumonia patients.…”

“…Indeed, current guidelines do not recommend routine testing for Legionella [11]. Rather, targeted testing of healthcare and severe community-acquired pneumonias is recommended-an approach that misses a significant percentage of Legionella cases [12]. Therefore, studies of Legionella pneumonia have artifactual biases toward more severe cases and presentations with conventionally attributed symptoms.…”