text: ptxP is the pertussis toxins promoter gene. There is a well documented emergence and global spread of ptxP3 strains evolving from and replacing the native ptxP1 strains, associated with an increased production of the toxin, and thus an increased virulence. Such spread has been documented in multiple countries, and sometimes but not always linked to the resurgence of pertussis in the end of the 20th century. Countries with a documented spread of ptxP3' include Australia, Denmark, Finland, Iran, Italy, Japan, the Netherlands, and Sweden.