Diagnostic value of the Binax NOW assay for identifying a pneumococcal etiology in patients with respiratory tract infection.

BACKGROUND AND PURPOSE Streptococcus pneumoniae is a common pathogen in respiratory tract infections which is usually underestimated with conventional tests, largely due to the fragility of the bacteria. This study assessed the diagnostic value of a rapid test (Binax NOW) for the detection of the pneumococcal antigen in urine. METHODS Unconcentrated urine samples from 1243 adults and 91 children hospitalized with respiratory tract infections were tested. RESULTS In all adults with respiratory tract infections, the diagnostic results were as follows: sensitivity, 29 (60%) of 48; specificity, 748 (92.2%) of 811; negative predictive value, 748 (97.5%) of 767; false-positive rate, 63 (68%) of 92. The diagnostic results were similar in adults with lower respiratory tract infections: sensitivity, 21 (64%) of 33; specificity, 658 (92.2%) of 714; negative predictive value, 658 (98.2%) of 670; false-positive rate, 56 (73%) of 77. In children with respiratory tract infections, the diagnostic results were: sensitivity, 4 of 4; specificity 18 (64%) of 28; negative predictive value, 18 of 18; false-positive rate, 10 of 14. The low specificity of the test in children may be due to frequent pneumococcal nasopharyngeal colonization. CONCLUSIONS High negative predictive values and high false-positive rates were found in both adults and children, indicating that a negative result may be more useful than a positive one in clinical practice. The high specificity of this test in adults indicates its potential value in the choice of initial antibiotic treatment by eliminating pneumococcal infection as a likely cause of respiratory tract infection in a proportion of patients.