The descriptive epidemiology of Streptococcus pneumoniae and Haemophilus influenzae nasopharyngeal carriage in children and adults in Kilifi district, Kenya.

BACKGROUND: Transmission and nasopharyngeal colonization are necessary steps en route to invasive pneumococcal or Haemophilus influenzae disease but their patterns vary geographically. In East Africa we do not know how these pathogens are transmitted between population subgroups nor which serotypes circulate commonly. METHODS: We did 2 cross-sectional nasopharyngeal swab surveys selecting subjects randomly from a population register to estimate prevalence and risk-factors for carriage in 2004. H. influenzae type b vaccine was introduced in 2001. RESULTS: Of 450 individuals sampled in the dry season, 414 were resampled during the rainy season. Among subjects 0-4, 5-9, and 10-85 years old pneumococcal carriage prevalence was 57%, 41%, and 6.4%, respectively. H. influenzae prevalence was 26%, 24%, and 3.0%, respectively. Prevalence of H. influenzae type b in children <5 years was 1.7%. Significant risk factors for pneumococcal carriage were rainy season (odds ratio [OR]: 1.65), coryza (OR: 2.29), and coculture of noncapsulate H. influenzae (OR: 7.46). Coryza was also a risk factor for H. influenzae carriage (OR: 1.90). Of 128 H. influenzae isolates, 113 were noncapsulate. Among 279 isolates of Streptococcus pneumoniae, 40 serotypes were represented and the distribution of serotypes varied significantly with age; 7-valent vaccine-types, vaccine-related types, and nonvaccine types comprised 47%, 19%, and 34% of strains from children aged <5 years. Among older persons they comprised 25%, 28%, and 47%, respectively (P = 0.005). CONCLUSIONS: The study shows that pneumococcal carriage is common up to 9 years of age and that the majority of serotypes carried at all ages are not covered specifically by the 7-valent pneumococcal conjugate vaccine.

Diagnosis of invasive pneumococcal disease among children in Kenya with enzyme-linked immunosorbent assay for immunoglobulin G antibodies to pneumococcal surface adhesin A.

Diagnostic techniques for invasive pneumococcal disease (IPD) in children are insensitive and underestimate both the burden of disease and the cost-effectiveness of pneumococcal conjugate vaccination (PCV). Consequently, there is little demand for the highly effective PCV outside the United States and Europe. In Kenya, diagnosis of pneumococcal pneumonia in adults was achieved with a sensitivity of 0.70 and a specificity of 0.98 using enzyme-linked immunosorbent assays (ELISAs) of paired plasma samples for immunoglobulin G (IgG) to pneumococcal surface adhesin A (PsaA). We aimed to validate the same technique in children. We assayed paired blood samples from 98 children with IPD, 95 age-matched children with malaria/anemia, and 97 age-matched healthy controls by using an ELISA for anti-PsaA IgG. Sensitivity and specificity were determined in IPD patients and healthy controls. Specificity (0.97; 95% confidence interval [CI], 0.91 to 0.99) and sensitivity (0.42; 95% CI, 0.32 to 0.52) were optimized at a 2.7-fold rise in anti-PsaA antibody concentration. Sensitivity was improved to a maximum of 0.50 by restricting testing to children of <2 years old, by excluding IPD patients who were not sampled on the first day of presentation, and by incorporating high existing antibody concentrations in the analysis. Assay performance was independent of nasopharyngeal carriage of pneumococci at recruitment. This assay improves on existing diagnostic tools for IPD in children but would still leave over half of all cases undetected in epidemiological studies. Effective diagnosis of pneumococcal disease in children is urgently required but poorly served by existing technology.