Evaluation of the impact of HIV-1 infection and density of common nasopharyngeal bacterial colonizers in South African children immunized with 7-valent pneumococcal conjugate vaccine

Abstract Background Due to limitations in standard culture methods, the impact of pneumococcal conjugate vaccine (PCV) immunization on nasopharyngeal bacterial carriage density is unclear, including among HIV-infected children. Methods The prevalence and density of serotype/serogroup-specific pneumococcal and other nasopharyngeal colonizing bacteria were investigated in archived swabs of HIV-infected and HIV-uninfected, PCV-7 immunized (at 6, 10 and 14 weeks of age) South African children collected at 9 and 16 months of age. During the course of the study, PCV-immunization of children in Soweto was limited to study-participants, as the vaccine had not been introduced into the public immunization program. Results At 9 months of age, the prevalence of overall pneumococcal colonization was lower in HIV-infected (58.6%) than HIV-uninfected children (69.9%, p = 0.02), mainly due to lower prevalence of non-vaccine-serotype colonization (27.8% vs. 40%, respectively; p = 0.047). The mean-log10 density of pneumococcal colonization was, however, higher in HIV-infected (4.81 CFU/ml) than HIV-uninfected pneumococcal colonized children (4.44 CFU/ml; p = 0.014); mainly due to higher mean-log10 density of PCV7-serotype colonization (4.21 vs. 3.72 CFU/ml; p = 0.014). No difference in the prevalence or density of overall pneumococci was found at 16 months of age. The prevalence of non-vaccine serotype colonization remained 1.7 fold higher in HIV-uninfected (60.4%) than HIV-infected children (50.9%, p = 0.049). Other differences included a lower prevalence of H. influenzae colonization in HIV-infected (42.3% and 56%) than HIV-uninfected children (64.2% and 73.4%) at both 9 and 16 months of age respectively; however, the density of colonization was similar. Conclusion Increased carriage density of residual PCV7-serotypes might cause HIV-infected children to have a higher risk of pneumococcal disease. The higher carriage density observed in HIV-infected children could be attributed to a combination of factors, including HIV treatment and impaired host immunity. Additional studies are needed.