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The objective of this study was to identify potential false-positive urine Legionella pneumophila (Legionella) enzyme immunoassay test results. A total of 107 consecutive patients with positive EIA tests were retrospectively analyzed over a 34-month period. Concurrent blood, urine, and sputum cultures, as well as chest radiographic findings, were reviewed in these patients. Twenty patients (19%) had no radiographic evidence of pulmonary disease despite a positive EIA test. In those 20 patients, 14 also had growth of non-Legionella bacteria. Of patients with an infiltrate or opacity on chest imaging, only 27 had Legionella sputum cultures obtained, with Legionella culture growth occurring in 7 (26%). Nine other patients had negative Legionella sputum cultures but the growth of another pathogenic organism in blood, sputum, and/or urine cultures. Pseudomonas aeruginosa was the most common organism isolated, found in 20% of patients in the entire cohort. Twenty-five patients (23%) were characterized as having probable false-positive Legionella urinary antigen EIA testing, and an additional 17 patients (16%) were characterized as having possible false-positive Legionella EIA tests. Our findings suggest that urine Legionella EIA tests may lead to a substantial number of cases being misdiagnosed as Legionaries’ disease in patients with non-Legionella bacterial colonization or infection.

Abstract Background Direct specimen sequencing (DSS) offers the promise of enhanced pathogen detection and disease diagnosis. Methods A single healthcare network, retrospective chart review over a 3-year period was completed for all cases in which DSS was submitted, in addition to conventional testing (CT) for workup of an infectious disease. We sought to compare results (concordance and discordance) from these 2 techniques in order to evaluate any additional yield from DSS over CT. Additionally, we calculated mean turnaround time (TAT) and average cost for obtaining DSS on all specimens. Results A total of 23 patients’ specimens were sent for DSS. DSS and CT concordance occurred in 91% (21/23) of cases. DSS testing was able to identify specific pathogens in 17.4% (4/23) of patients, out of which 4% (1/23) were discordant. The respective mean TAT and total cost per specimen for DSS were 6 days and $821.52 (range $573–$1590), respectively. Conclusions In our limited cohort of patients, there was significant concordance between the 2 testing modalities primarily due to negative tests. DSS did not provide significant additional yield in the infectious diagnosis in our cohort compared to CT. Short TAT may provide advantage in the detection of fastidious organisms, but high cost remains a limitation. Larger sample size may reveal a clinically meaningful difference.