Bordete//a pertussis specific Immunoglobulin G antibody levels among asymptomatic individuals aged 4-24 years admitted to two selected hospitals in Sri Lanka

Abstract

INTRODUCTION: Pertussis continues to circulate in the community and cases among adolescents and adults have been increasing. Waning of pertussis-specific immunity following natural infection or immunisation may contribute to the persistent circulation. Even though it is not included in the extended programme of immunization in Sri Lanka, the booster doses including the adolescent booster dose of dTap, (acellular pertussis) are included into the list of recommended immunizations in several countries. Even though the protective titre yet not established, information on immunity to pertussis in this age group is needed before any vaccination policy can be considered. OBJECTIVES: To determine the antibody levels against pertussis toxin to determine the need and the optimal age for booster immunization. METHODS: The quantitative determination of specific IgG antibodies to Bordetella pertussis toxin was done by the ELISA using sera of 385 asymptomatic individuals aged 4-24 years admitted to surgical units of Lady Ridgeway Hospital, Colombo and Colombo South Teaching Hospital, Kalubowila. Mann-Whitney U test and Kruskal-Wallis test were used in analysis and p<0.05 was taken as significant. RESULTS: Median age was 12 years (IQR 8-19) with 212 (55.1 %) females. The median (IQR) anti PT antibody level was 3.31 lU/ml (0.73-15.12) and 352 (91%) had anti PT level <55 ID/ml. Median {IQR) anti PT levels were 3.18 ILJ/ml (0.591 -8.00) for 4-7 years, 1.43 Ill/ml (0.336-6.27) for 8-11 years, 4.28 lU/ml (0.978-13.39) for 12-15 years, 6.14 lU/ml (1.44-63.25) for 16-19 years and 4.89 lU/ml {1.11 -16.78) for 20-24 years and all of these difference were statistically significant (Spearman Correlation Coefficient P=0.0121). Females (p<0.003) and those having a sibling above 12 years (p=0.017) had significantly higher anti PT lev els. CONCLUSION: The majority of the study population, especially 8 to 11 years age group had very low anti PT IgG levels. The infection may occur in early adolescents, A booster dose of acellular pertussis vaccine could be considered.