Rapid screening for bacteriuria by light scatter photometry (Autobac): a collaborative study

Abstract

A total of 2720 urine specimens from 3 laboratories were evaluated by Autobac (Pfizer Diagnostics) and were compared with simultaneous colony counts for evidence of bacteriuria. Of 599 specimens with a colony count of .gtoreq. 105 colony-forming units/ml, 93.8% were detected within 6 h. This detection rate increased to 97% of 447 positive urine specimens when only specimens from patients not on antimicrobials were evaluated. The majority (77.9%) of positive specimens were detected as early as 3 h. Those specimens with .gtoreq. 105 colony-forming units/ml, which were negative by Autobac at 6 h, included organisms which are frequently considered to be contaminants (diphtheroids, lactobacilli, .alpha. and .gamma. streptococci, yeasts and Staphylococcus epidermidis), or were from patients who were being treated with antimicrobial agents. Of 2121 urine specimens with colony counts of < 105, 98.1% were correctly determined to be negative by Autobac at 3 h. This percentage decreased to 86.0 at 6 h. The majority of these false-positive specimens were those with colony counts of 104-105 colony-forming units/ml. There appeared to be no major difference in results from the 3 laboratories or among the 4 lots of broth used in this study.