Evaluation of the IDS RapID SS/u system for rapid identification of urinary microorganisms

The accuracy of a new rapid identification system for common urinary pathogens was compared with that of conventional methods and of miniaturized 18-24-hour identification panels. The rapid system, RapID SS/u (Innovative Diagnostic System Inc., Atlanta, GA) is a non-growth-dependent micro-method that identifies selected gram-negative bacilli, gram-positive cocci, and yeasts in two hours by detection of constitutive enzymes acting on chromogenic substrates. A total of 185 representative clinical urinary isolates were tested, including 24 gram-positive cocci, 140 gram-negative bacilli, and 21 yeasts. Identifications by the rapid system were compared with the ones obtained by reference conventional methods for gram-positive cocci and yeasts. For gram-negative bacilli, identifications were compared with the ones obtained by MicroScan Combo Panel (American MicroScan, Mahwah, NJ), and all discrepancies were resolved by testing with API 20E (Analytab Products, Plainview, NY). Overall, the RapID SS/u system correctly identified to genus 160 of 185 isolates (86.5%). For 14 additional isolates (7.6%) the system provided probability overlap identifications that required further testing. Two (1%) isolates failed to be identified, and nine isolates (4.9%) were misidentified by the system. Discrepancies involved five strains of Citrobacter, one Enterobacter, one Morganella, and one Providencia species. The authors conclude that the RapID SS/u system provided rapid and accurate genus identification of most microorganisms commonly isolated from urine.