ANALYSIS OF THE PREVACCINE POPULATION OF NONCAPSULATE HAEMOPHILUS-INFLUENZAE AND IDENTIFICATION OF A PUTATIVE EPIDEMIC CLONE

For six months prior to the introduction of Haemophilus influenzae ser otype b vaccines, all noncapsulate Haemophilus influenzae received by our laboratory were characterised by biotyping, antibiogram, outer-mem brane protein profiling, and ribotyping, Simpson's index of diversity (SID) showed the population was heterogeneous with multiple clones, Th e study identified a clone within noncapsulate Haemophilus influenzae biotype II that caused more disease than other strains. This clone was shown to have previously caused two outbreaks of respiratory disease and to possess a small extrachromosomal plasmid encoding ampicillin re sistance. The study shows that describing the diversity within a bacte rial population with SID may negate the need for retrospective subtypi ng comparisons.