Biotype of Haemophilus influenzae: Correlation with Virulence and Ampicillin Resistance

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Abstract
Biotype and serotype were determined for 473 isolates of Haemophilus influenzaefrom 399 children. Patients with invasive disease usually had serotypable (86%) and biotype 1 (80%) isolates. Respiratory isolates from well children and children whose illness was not caused. by H. influenzae were rarely serotypable (1%) or biotype 1 (8%). Respiratory isolates from children whose illness was possibly or probably related to H. influenzae and isolates from children with cystic fibrosis were more frequently biotype 1, serotypable, or both (P < 0.01 for all comparisons). Ten (67%) of 15 children with acute otitis media due to H. influenzae had tympanocentesis isolates which were biotype 1; only one isolate was serotypable. Isolates from inflamed conjunctivae had biotypes and serotypes similar to respiratory isolates from well children. Ampicillin resistance was less frequent among biotype 1 isolates (9%) compared with other biotypes (19%) (P < 0.01). The data suggest that H. influenzae is biochemically heterogeneous and that noncapsular factors, frequently predictable by biotype, contribute to virulence.