Serotyping of Haemophilus influenzae a comparison of co-agglutination with countercurrent--immunoelectrophoresis and slide--agglutination.

30 out of 55 strains of H. influenzae could be assigned to one of the six serotypes A--F by slide agglutination, countercurrent-immunoelectrophoresis or co-agglutination. While slide-agglutination appeared less reliable due to non-specific agglutinations countercurrent-immunoelectrophoresis was of high specificity. No cross reactions were encountered in this test and results were unambiguously to evaluate. Co-agglutination is attractive because of its rapidity and simplicity without any need of special equipment. It was found to be of increased sensitivity in detecting type B capsular antigen when compared with countercurrent-immunoelectrophoresis, the problem of cross-reactions remains to be solved however. The use of co-agglutination for serotyping H. influenzae strains in combination with countercurrent-immunoelectrophoresis can be recommended.