Time Trend of the Sensitivity of the Pneumococcal Urinary Antigen Test for Diagnosing Pneumococcal Community-Acquired Pneumonia: An Analysis of 15-Year, Prospective Cohort Data

INTRODUCTION: Whether the sensitivity of the BinaxNOW Streptococcus pneumoniae urinary antigen test kit (BinaxNOW), adjusted by some variables including vital signs, laboratory examinations and pneumonia severity, has been decreasing is unknown. The aim of the present study was to investigate whether BinaxNOW sensitivity has decreased recently and to identify the predictors of the BinaxNOW result, including the time trend. METHODS: This prospective cohort study enrolled consecutive patients with pneumococcal community-acquired pneumonia who were hospitalised at Kurashiki Central Hospital from January 2001 to December 2015. Pneumococcal community-acquired pneumonia was defined as positive blood or pleural effusion or sputum culture results. To evaluate the effect of the time trend for the sensitivity of BinaxNOW, time series regression analysis was performed. In addition, predictors of the BinaxNOW result were examined by multivariable analysis using variables such as sex, vital signs, blood tests such as C-reactive protein, albumin, blood urea nitrogen, creatinine, white blood cell count, haematocrit and platelets, antibiotic pre-treatment, bacteraemia, and pneumonia severity, in addition to time trend and seasonality. RESULTS: A total of 446 patients were included. BinaxNOW sensitivity showed a significant, gradual decrease from 2001 (81.3%) to 2015 (48.7%). On multivariable analysis [odds ratio (95% confidence interval)], bacteraemia [2.516 (1.387–4.561), P = 0.002] was a predictor of a positive BinaxNOW result, whereas male sex [0.467 (0.296–0.736), P = 0.001], white blood cell count [0.959 (0.930–0.989), P = 0.008] and the time trend per year [0.900 (0.859–0.943), P < 0.001] were predictors of a negative BinaxNOW result. CONCLUSIONS: The sensitivity of BinaxNOW decreased over a 15-year period. We should be careful when interpreting BinaxNOW results in daily clinical practice, and the development of a new kit with good sensitivity is anticipated. TRIAL REGISTRATION NUMBER: UMIN000004353.