In response to the growing number of notified cases of pertussis (whooping cough) in the vaccinated population, the aim of this study is to determine the concentration of IgG antibodies against the pertussis toxin (PT) in the population of children. The other aim investigated in this study is to determine the number of children with the symptom of long-term cough (lasting more than three weeks), where the diagnosis of pertussis has been established. The method of ELISA was used to examine 254 samples of sera from children at the age of 0 – 18 years, who had visited the immunological-allergological outpatients’ as well as that of general practitioner for children and adolescents in the period of 29 November 2004 to 14 March 2005 and who were taken blood samples for other examinations indicated. Ten children, who were not vaccinated against pertussis proved to have negative IgG against pertussis. Among the remaining 244 vaccinated children, 180 individuals (73%) had negative IgG antibodies against pertussis. The long-term cough in anamnesis was detected in 71 children of the group. In 29 of them (40%) the diagnosis of pertussis was established. The data obtained indicate that pertussis should be considered in differential diagnosis of long-term cough and, in certain conditions, the serological determination of IgG antibodies against PT by ELISA in a single sample may be considered as sufficient to confirm or exclude this diagnosis. It appears suitable to consider an adjustment of vaccination schedule and to include re-vaccination of children around the age of nine years with acellular vaccine.

        Key words: pertussis, vaccination, pertussis toxin, cough