Background: Despite the addition of two teteanus-diphteria-acellular-pertussis (Tdap) booster doses in 2005 and 2008, the Israeli Ministry of Health surveillance data reveals a marked increase in the incidence of pertussis. We aim to assess the rate of positivity in the laboratory diagnosis and changes in B. pertussis genotype and phenotype following the introduction of two Tdap boosters.
Methods: For polymerase chain reaction (PCR), B. pertussis detection was based on the amplification of Insertion Sequence 481. Pulse field gel electrophoresis (PFGE) utilized the SpeI restriction enzyme. The Pertactin (Prn) protein was detected by western immunoblot.
Results: There was a change in the B. pertussis PCR positivity, 40/408 (9.8%), 66/491 (13.4%), 111/504 (22%) and 87/572 (15.2%) for 2010, 2011, 2012 and 2013, p<0.001, respectively. A similar trend was evident for positive- culture specimens. Several PFGE restriction patterns from 2009-2012 were identified and referenced 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 new profiles, E (n=2, 5%), F (n=1, 3%), G (n=3, 8%), H (n=1, 3%), and I (n=2, 5%) emerged. The proportion of Prn negative isolates increased significantly over 2005-2006, 2011-2012 and 2013-2014, 1/15 (6.6%) vs. 1/17 (7.1%) vs. 11/33 (33.3%), p<0.03.
Conclusions: The increase in pertussis laboratory detection is associated with changes in B. pertussis genetics and the circulation of isolates not expressing Prn. Studies should explore whether these divergent strains are caused by high Tdap coverage.
