Diagnosis of bacteremia in children by quantitative direct plating and a radiometric procedure

Abstract

During a 1-year period, three bacteriological systems for detecting bacteremia in children were analyzed, namely, the BACTEC system (Johnston Laboratories, Inc., Cockeysville, Md.), the Fisher/Lederle bottle (Lederle Diagnostics, Pearl River, N.Y.), and a direct plating method of blood termed quantitative direct plating (QDP). Of 2,123 blood cultures, 135 (6.4%) were positive; Haemophilus influenzae type b, Neisseria meningitidis, and Streptococcus pneumoniae accounted for 3.4%, representing 61 patients, other pathogens accounted for 0.6%, and contaminants accounted for 2.4%. Of 72 cultures yielding H. influenzae, N. meningitidis, and S. pneumoniae, 60 were recovered by both broth systems, 2 by BACTEC only and 10 by Fisher/Lederle bottle only. The BACTEC system failed to register a positive growth index reading by 24 h in 15 cultures which were positive for H. influenzae, even though growth had occurred, as shown by positive subculture and microscopy at this time. QDP detected 89% of the cultures positive for H. influenzae and N. meningitidis, of which 55% yielded results before either broth procedure. Only 50% of the cultures positive for S. pneumoniae yielded growth on QDP. This difference in the recovery rate probably is accounted for by the number of organisms in the blood. Thus, more than 100 organisms per ml of blood were found in 71% of cultures positive for H. influenzae and N. meningitidis but in only 7% of those positive for S. pneumoniae. These studies, then, have revealed that H. influenzae, which grew well in BACTEC broth, did not, however, give a significant growth index reading during day 1 of incubation, in contrast to N. meningitidis and S. pneumoniae. The QDP system not only provided information on the magnitude of bacteremia due to H. influenzae and N. meningitidis but frequently allowed earlier diagnosis and, thus, proved to be a valuable, simple, and inexpensive supplementary technique for broth cultures, although not for the diagnosis of S. pneumoniae bacteremia.