Nasopharyngeal colonization of infants in southern India with Streptococcus pneumoniae

To investigate the dynamics of nasopharyngeal colonization with Streptococc us pneumoniae, and to determine the prevalent serogroups/types (SGT) and th eir antimicrobial susceptibility, we studied 100 infants attending our well -baby clinic. Nasopharyngeal swab specimens were obtained at 6, 10, 14, 18 and 22 weeks and at 9 and 18 months of age and submitted for culture, serot yping and antimicrobial susceptibility testing of S. pneumoniae. Colonizati on with pneumococcus was seen on at least one occasion in 81 infants. The m edian age of acquisition was 11 weeks and the median duration of carriage w as 1.3 months. The common SGTs identified were 6, 19, 14 and 15. SGT 1, whi ch was a common invasive isolate in children in our hospital during this pe riod, was not isolated from these children. Sequential colonization by 2, 3 or 4 SGTs was observed in 18, 5 and 2 children, respectively. Resistance t o penicillin, chloramphenicol, cotrimoxazole and erythromycin was observed in 0, 13 (6 %) 11 (5 %) and 5 (3 %) isolates, respectively. There was a sig nificant difference in susceptibility to cotrimoxazole between colonizing a nd invasive isolates (5 % vs. 40%, P < 0.0001).