Bordetella pertussis seroprevalence among 6-14 years old school children in Ankara, Turkey

Bordetella infection remains to have a high burden in developing countries. Cases occur among older children, adolescents and adults due to waning of vaccine induced immunity and this group possesses high risk for pre-immunized infants.
The study is conducted in November 2004 in two government primary schools in Ankara with 1103 and 1127 six to fourteen years old students. A questionnaire form is sent to the parents of the children and the children whose parents gave written consent were included in the study. Six hundred seventy nine (61.6%) students from the first and 776 students (68.9%) from the second school were enrolled in the study. Seven hundred fifty of the students were male (51.5%) and 705 were female (48.5%). The Bordetella pertussis Anti-PT IgG antibodies were detected by ELISA method. The antibody titers were grouped as <10IU/ml (seronegative), 10-99.99IU/ml (seropositive) and ≥100 IU/ml (recent infection). A total of 61 students (4.2%) were seronegative, 1123 (77.2%) were seropositive, and the antibody titers of 271 students (18.6%) suggested recent infection. Both the seronegativity (5.4%) and recent infection (23.5%) prevalences were significantly higher in 12-14 years age group when compared to 6-8 (3.8, 19.1%) and 9-11 (3.6, 14.2%) age groups. The antibody titers were also higher among 12-14 years age group (p<0.05). The seronegativity and recent infection prevalences were not different between male (3.9, 9.1%) and female (4.5, 18.2%) students (p>0.05). There was no difference between seronegativity and recent infection prevalences with respect to presence of vaccination card, history of pertussis immunization and pertussis disease.
Our results suggest that the seronegativity and recent infection prevalences are high among 12-14 years old students. Waning of vaccine-induced immunity may be the reason of the high incidence of pertussis in school-children and further vaccination schedules with acellular pertussis vaccine should be considered beyond childhood.