Background: In recent years, despite widespread vaccination, Bordetella pertussis has become increasingly prevalent. Bacterial genetic drift is thought to prompt the emergence of new strains. We previously described two dominant, closely related pulsed-field gel electrophoresis (PFGE) profiles, 2007-2008, named A and B. Profiles C and D were also identified. The predominant PFGE profile A, had the same PFGE cluster as the dominant European strain, 1999- 2004 known as PFGE cluster IVβ, whereas profile B was identical to cluster IVα.
Aim: To analyze selected circulating pertussis isolates utilizing PFGE during the high incidence rate years, 2009-2012, one year after the introduction of the sixth catch-up dose.
IMethods: All the Bordetella pertussis isolates (n=38) were analyzed by PFGE using SpeI as restriction enzyme. A chi-square statistical analysis was performed using Winpepi program.
Results: Several PFGE restriction patterns from 2009-2012 were identified and compared to our 2007-2008 profiles. Profile A decreased from 54% (n=44) to 26% (n=10), p<0.006, whereas B increased from 41% (n=34) to 50% (n=18), p>0.43, respectively. Profiles C and D disappeared and five new profiles, E (n=2, 5%), F (n=1, 3%), G (n=3, 8%), H (n=1, 3%), and I (n=2, 5%) emerged.
Conclusions: Following the implementation of additional vaccine doses, a significant decrease in the frequency of PFGE profile A (cluster IVβ) occurred as well as an increase of profile B (cluster IVα). New PFGE patterns emerged. Similar profile dynamics have also been described in Europe. Further studies should explore whether this genetic drift may be prompted by the recent vaccine selection pressure.
