In view of the apparent unusual nature of our findings the majority of the H parainfluenzae strains were tested by slide agglutination methods with H influenzae types a-d specific antisera and in no instance was there agglutination. The same strains were also examined by immunofluorescence using an H influenzae polyvalent antiserum pool and H influenzae type b antiserum since such methods, as described by Catlin (Am J Dis Child 120:203, 1970), are more sensitive than agglutination. In no instance was there immunofluorescence.
Quality control studies on our lots of X and V strips and more recent confirmation by the Center for Disease Control (CDC), Atlanta, or identification of similar species isolated from clinical specimens at the Mayo Clinic would seem to preclude technical problems. As yet unresolved, however, by ourselves and by the CDC is whether or not such species represent H parainfluenzae of H paraphrophilus. Differentiating characteristics, using conventional