Three latex agglutination tests compared with gram staining for the detection of bacteria in cerebrospinal fluid

Three commercially available latex agglutination tests and the Gram stain were evaluated for their ability to detect Haemophilus influenzae, Streptococcus pneumoniae and Neisseria meningitidis in cerebrospinal fluid (CSF) specimens from 160 patients suspected of having meningitis. Bactigen detected 86% of all culture-positive CSF specimens, whereas Wellcogen detected 80%, Bio Merieux 59% and Gram stain 94%. Bactigen and Wellcogen detected 84% of cases of meningitis caused by H. influenzae, whereas Bio Merieux detected 53% and Gram stain 90%. Of the 27 cases of Strept. pneumoniae meningitis, all were detected by Gram stain, 96% by Bactigen, 89% by Wellcogen and 74% by Bio Merieux. For N. meningitidis, which included four isolates of group B and one group W135, detection was 80% with the Gram stain, 40% with Bactigen and 20% with Wellcogen. False-positive results were observed with Bactigen and Bio Merieux respectively on 5% of culture-positive CSF specimens for organisms other than the test organisms. With the exception of faulty batches of individual kits of Bactigen (H. influenzae B) and Wellcogen (Strept. pneumoniae) respectively, false-positives were not obtained on the 63 culture-negative CSF samples. Bactigen and Wellcogen were equally efficacious in detecting H. influenzae B. Bactigen was marginally superior to Wellcogen for the detection of Strept. pneumoniae. Bio Merieux was the least sensitive of the three latex agglutination kits tested. The Gram stain was found to be at least as sensitive or superior to latex agglutination for detecting H. influenzae B, Strept. pneumoniae and N. meningitidis in CSF specimens from patients with bacteriologically proven meningitis.