Seroprevalence of IgG antibodies to pertussis toxin in the Slovene population.

ABSTRACT

BACKGROUND: The use of pertussis vaccines has reduced the morbidity and mortality of whooping cough. Immunity following the natural disease or vaccination is not life-long and reinfections causing an increase of pertussis antibodies can occur. In this study, the distribution of IgG antibodies to pertussis toxin (anti-PT IgG) among different age groups in Slovenia was determined. METHODS: The seroprevalence of anti-PT IgG antibodies to Bordetella pertussis was investigated in 3418 persons (49.1% males). The population under study was stratified into 27 age groups. The serological results were assigned to five groups, according to their titer levels. The geometric mean titers (GMT) were calculated. RESULTS: In 11.5% sera tested, no IgG antibodies to pertussis toxin were detected. High titers (> or =125 U/ml) were confirmed in 2.3% sera. There were no statistically significant differences between age groups in the proportion of antibody levels. Pre-school children from three to five years of age had the lowest anti-PT IgG GMTs (9.6-10.7 U/ml). Vaccinated children (aged from one to two years) and adolescents from 17-18 years of age had the highest GMTs (>20 U/ml). GMTs were not statistically significantly different between males and females. CONCLUSIONS: The study demonstrated an early decline of anti-PT IgG after vaccination. According to the serological profile, school-age children and adolescents have the highest rate of infection. The large proportion of seropositive adults indicates that reinfection with B. pertussis is relatively common.