Increase in Genetic Diversity of Haemophilus influenzae Serotype b (Hib) Strains after Introduction of Hib Vaccination in The Netherlands

Abstract

Recently, there has been an increase in The Netherlands in the number of cases of invasive disease caused by Haemophilus influenzae serotype b (Hib). To study a possible change in the Hib population that could explain the rise in incidence, a multiple-locus variable number tandem repeats analysis (MLVA) was developed to genotype H. influenzae isolates. The MLVA enabled the differentiation of H. influenzae serotype b strains with higher discriminatory power than multilocus sequence typing (MLST). MLVA profiles of noncapsulated H. influenzae and H. influenzae serotype f strains were more heterogeneous than serotype b strains and were distinct from Hib, although some overlap occurred. The MLVA was used to genotype a collection of 520 H.

Characteristics of Haemophilus influenzae Type b Responsible for Meningitis in Poland from 1997 to 2004

“…This technique, used in the present study, revealed six STs previously described and four new STs among the Polish encapsulated H. influenzae isolates tested. The most prevalent ST among the Hib isolates was ST6, which had been previously observed in the United States, Norway, Russia, The Netherlands, and the Czech Republic (www.mlst.net) (15,18,27). In the last country, 22 out of the 26 Hib isolates tested belonged to the ST6 (15).…”

“…This fact is especially well known for Hib isolates, which are genetically homogenous and which the relationship has been found even for isolates originating from different countries and from different decades (18,21,32). However, in The Netherlands an increase in the genetic diversity of the Hib population after the introduction of vaccination against Hib has been reported recently (27).…”

“…In the Dutch study, in which 241 Hib isolates were analyzed by MLST, 76.3% of them belonged to ST6 (27). The second most common ST in our study, ST92, an SLV of ST6 in the recA locus, was found in Russia, whereas ST44 was found in the United States, England, Ghana, Kenya, and The Netherlands (www.mlst.net) (18,27). Other STs present in our study, ST80, -93, and -95, were found in Russia previously, and, additionally, ST80 was found in Kyrgyzstan.…”

“…All over the world the majority of severe infections related to this species are caused by H. influenzae type b (Hib). In countries where mass vaccination against Hib has been introduced, a dramatic reduction in the number of cases, as well as a noticeable decline of carriage rate in the population, has been reported (20,24,25,27). Although highly recommended, vaccination against Hib in Poland is on a voluntary basis and not free of charge.…”

Molecular Aspects ofMoraxella catarrhalisPathogenesis

“…Subsequent MLST of N. meningitidis yielded 47 sequence types (STs) from 92 strains (128), and for M. catarrhalis, 173 MLST STs were observed among 268 isolates (153). In contrast, MLST of H. influenzae serotype b, considered to be monomorphic (clonal), yielded 29 STs from 241 strains (129). These results indicate that the M. catarrhalis species comprises a panmictic population of isolates, although serosensitive lineage isolates appear to be more clonal than the seroresistant lineage (153).…”