Genotyping of type b Haemophilus influenzae strains, comparison of strains collected before and during vaccine availability

Five hundred and seventy-eight strains of type b Haemophilus influenzae (521 isolated in children, and 57 in adults) were compared using pulsed-field gel electrophoresis (PFGE) to assess strain evolution and to study the impact of the generalization of anti-Haemophilus b (anti-Hib) vaccination in France. Among these strains, 398 (including 342 from meningitis) were isolated in 1985-1992 (pre-vaccination era), 39 (including 31 from meningitis) in 1993 (year of the generalization of anti-Hib vaccination), and 141 (including 50 from CSF) in 1994-2001 (vaccination era).

A total of 102 PFGE patterns (patterns for 1-101 isolates) were obtained after SmaI restriction of the 578 strains. The strains isolated in children were distributed in 96 patterns, and those isolated in the adult in 34 patterns. The strains isolated during the pre-vaccination era presented 94 patterns. During the vaccination era, 50% of the patterns disappeared and 12 new patterns (11.7%) including 15 strains were observed. The strains belonging to the new patterns (including the two observed in 1993) were isolated in adults (n=7) from blood culture and bronchial secretions, and children (n=9) from CSF, blood culture, and bronchial secretions. In children, among the strains associated to vaccination failure, two presented with a new pulsotype.

There is no evidence that the vaccination program brought about any drastic modifications in the type b strains causing meningitis or in the other type b strains in circulation whether in adults or children.