Comparison of the Denka Seiken slide agglutination method to the quellung test for serogrouping of Streptococcus pneumoniae isolates.

This study compared a slide agglutination test (Denka Seiken, Tokyo, Japan) to the "gold standard" quellung reaction (Pneumotest; Statens Serum Institut, Copenhagen, Denmark) for the serogrouping of pneumococci. Two hundred clinical isolates of Streptococcus pneumoniae were used for the comparison. Each assay was performed according to the manufacturer's instructions. There was an overall agreement of 95.7% between the two methods. Only 4 of 10 isolates of serogroup 22 were detected with the slide agglutination assay. Two isolates that were untypeable by the Pneumotest method were typed as serogroups 6 and 31 by the slide agglutination method. The Pneumotest method was unable to type 22 isolates, and the slide agglutination method was unable to type 16 isolates. The slide agglutination method compares favorably with the Pneumotest method and is easier to perform and to interpret.