Dynamics of the population structure of Bordetella pertussis as measured by IS1002-associated RFLP: comparison of pre- and post-vaccination strains and global distribution.

The effect of temporal and geographic factors on the population structure of Bordetella pertussis was studied using IS1002-based RFLP analysis. Among the 106 strains analysed, 36 different RFLP types were observed. For the Dutch strains, there was evidence for a shift in the population structure in time since the majority of strains were found in different families of related strains in successive periods. Most pronounced were the differences observed between 1950-1954 and later periods. This difference may have been caused by the introduction of the whole-cell vaccine in 1953, resulting in the expansion of strains which are less affected by vaccine-induced immunity. Strains with RFLP types identical to the vaccine strains were observed in the period 1950-1954, but not later, suggesting a decreased frequency of such strains due to vaccination. Analysis of strains from the 1994 Dutch pertussis epidemic revealed that 71% of the strains belonged to two RFLP types, indicating that pertussis epidemics are caused by clonal expansion. IS1002-based RFLP analysis of strains from different countries suggested a partial geographic isolation of B. pertussis populations. One RFLP type was found to have a wide distribution in time and in space.