Performance of a New Rapid Immunoassay Test Kit for Point-of-Care Diagnosis of Significant Bacteriuria

Abstract

dUrinary tract infections (UTIs) are frequently encountered in clinical practice and most commonly caused by Escherichia coli and other Gram-negative uropathogens. We tested RapidBac, a rapid immunoassay for bacteriuria developed by Silver Lake Research Corporation (SLRC), compared with standard bacterial culture using 966 clean-catch urine specimens submitted to a clinical microbiology laboratory in an urban academic medical center. RapidBac was performed in accordance with instructions, providing a positive or negative result in 20 min. RapidBac identified as positive 245/285 (sensitivity 86%) samples with significant bacteriuria, defined as the presence of a Gram-negative uropathogen or Staphylococcus saprophyticus at >10 3 CFU/ml. The sensitivities for Gram-negative bacteriuria at >10 4 CFU/ml and >10 5 CFU/ml were 96% and 99%, respectively. The specificity of the test, detecting the absence of significant bacteriuria, was 94%. The sensitivity and specificity of RapidBac were similar on samples from inpatient and outpatient settings, from male and female patients, and across age groups from 18 to 89 years old, although specificity was higher in men (100%) compared with that in women (92%). The RapidBac test for bacteriuria may be effective as an aid in the point-of-care diagnosis of UTIs especially in emergency and primary care settings. Bacterial urinary tract infections (UTIs) are a common clinical problem across the age spectrum in both genders (1). Women and girls are disproportionately affected by UTIs, with the lifetime risk estimated at Ͼ60% (2). In the United States, the overall annual cost of diagnosis and treatment of UTIs is considerable, estimated at $2.3 billion in 2010 (1). Gram-negative bacteria are the causative agents in up to 95% of uncomplicated UTIs in women, with Escherichia coli responsible for 70% to 90% (1).Diagnosis of UTI remains problematic in certain settings. The presence of uropathogenic bacteria in urine is the hallmark of UTI, and urine culture is the gold standard method for determination of clinically relevant bacteriuria. However, the 24-to 48-h delay in obtaining urine culture results has presented a longstanding need for more rapid diagnostic methods. Currently available rapid methods for detection of bacteriuria, including microscopy and test strips for detecting nitrite, have been shown to have poor sensitivity (3-5). A meta-analysis of 34 studies evaluating the accuracy of nitrite test strips across settings and populations found a mean sensitivity of 48% (using a definition of 10 5 CFU/ml for significant bacteriuria) (6). Microscopic urinalysis and urine Gram staining, two relatively laborious methods, have been shown by several studies to lack sensitivity below 10 5 CFU/ml and to have poor specificity (4,5,7,8). Guidelines for UTI from the Infectious Disease Society of America (IDSA) do not recommend urine culture for most cases of acute uncomplicated cystitis, the most common UTI presentation, and do not address laboratory methods for diagnosing UTI (9).An accurate ...

Validity of microscopy for diagnosing urinary tract infection in general practice – a systematic review

“…New diagnostic POC testing methods, such as rapid immunoassay test, are being developed and could have a place in testing for UVI in future studies [30].…”

New and developing diagnostic technologies for urinary tract infections

“…Dipstick tests for urine nitrite and leukocyte esterase are widely used lateral flow assays, but they are limited by shortcomings of poor sensitivity 6,39 . In 2015, a new antibody-based lateral flow assay (RapidBac), which is currently approved for veterinary use, was evaluated in a human study for rapid detection of bacteriuria 41 . This test is comprised of two monoclonal antibodies, one specific for Enterobacteriacea and a broader-spectrum antibody against Gram-negative and several Gram-positive species including Staphylococcus , Enterococcus , and Actinomyces spp.…”

“…This lateral flow immunoassay had a sensitivity of 86% for samples with ≥10 3 cfu/ml bacteria with a specificity of 94% when tested in 966 human urine samples compared with standard culture (set at 100% sensitivity and specificity) and a sensitivity of 96% for Gram-negative bacteria present at ≥10 4 cfu/ml (REF. 41). These data are promising, but further testing of this assay in a multicentre prospective study is needed to confirm the accuracy of the test.…”

Paper and thread as media for the frugal detection of urinary tract infections (UTIs)

“…That same year, the rapid detection of bacteriuria was studied using an antibody-based lateral flow assay (RapidBac). Rigorous tests were conducted to determine the sensitivity and specificity of the device, ultimately concluding that the RapidBac test for bacteriuria may be valuable in emergency and primary care settings as UTI point-of-care diagnostics [ 105 ].…”