F2 and pertussis: In this study, we wanted to determine concentrations of IgG antibodies to PT among healthy population in Guangdong province, in order to gain an insight into seroepidemiology of pertussis in China, incidence of pertussis infection estimated in adolescents and adults and level of anti-PT IgG antibodies in children (less than 7 years old) vaccinated with DTP vaccines before the life of two years.