Longitudinal study on pneumococcal carriage during the first year of life in Bangladesh

Background: The strong herd immunity effect and the serotype replacement associated with the use of the pneumococcal conjugate vaccine have highlighted the importance of asymptomatic pneumococcal carriage. To describe the development of pneumoccoccal carriage in a developing country setting we carried out a longitudinal pneumococcal carriage study in Bangladesh. Methods: Ninety-nine children, born in Savar, Bangladesh between May 2000 and April 2001, were enrolled in the study with their families. Nasopharyngeal samples were collected at prescheduled 2-4 week intervals from the index children and from their family members. The nasopharyngeal swabs were cultured for pneumococcal growth and pneumococci were identified and serotyped by standard methods. Results: We collected 1459 samples (92% of those planned) from the 99 index children and 2865 samples from other family members. The data showed high point prevalences of pneumococcal carriage among newborns (40-50% from 8 weeks of age on), a rapid pneumococcal acquisition with age (50% of the children had been colonized by pneumococci at least once by the age of 8 weeks) and a wide range of different serogroups/types (SGT). SGT 6 and 19 accounted for 35% of the pneumococci isolated from children < 1-year-old. followed by SGT 15, 23, and 10 for a total of 56%. The SGT distribution in children up to 9-year-old was similar to that among the < 1 year olds, with SGT 6 and 19 predominating. Older children and adults differed from the younger children by not having clearly predominating SGTs. Conclusions: The features found in our study are typical of pneumococcal carriage in developing countries. We believe that results from longitudinal modeling of carriage based on these extensive data can have wide geographic application.