Genetic diversity and population dynamics of Bordetella pertussis in China between 1950-2007.

Pertussis is an acute respiratory infectious disease caused by the bacterium Bordetella pertussis. Although pertussis vaccination was introduced in the 1960s, pertussis is still an endemic disease in China. To better understand the genetic diversity of the Chinese B. pertussis population, we characterized 115 clinical isolates obtained in China during 1950-2007 using multilocus variable-number tandem repeat analysis (MLVA). Forty-six different B. pertussis MLVA profiles (MTs) were identified, of which 13 were new MTs. Analysis using a minimum-spanning tree showed that distinct MTs were prevalent during different periods, suggesting that a dynamic change in B. pertussis MTs occurred over time in China. The predominant MTs in recent isolates from China were different from those of many developed countries. A decreasing trend in genetic diversity of the B. pertussis population was observed following the introduction of pertussis vaccines. Similar to the pertactin 2 (prn2) allele, the novel pertussis toxin promoter (ptxP3) allele first emerged in 2000, but unlike trends elsewhere, ptxP1 remained predominant among the isolates, further reflecting the unique temporal trends in the B. pertussis population in China. Our results suggest that temporal changes in the B. pertussis population may be closely associated with vaccination coverage and the vaccine types used. These data may lead to an improved understanding of the virulence mechanism of B. pertussis and facilitate new strategies for controlling this infectious disease.