HypothesisGeographical differences in invasive pneumococcal disease rates and serotype frequency in young children
Section snippets
IPD incidence
Signs of invasive pneumococcal disease range from mild, usually transient, occult bacteraemic without a focus of infection, to localised infections, bacteraemic pneumonia, sepsis, and meningitis. In most cases, IPD is detected by blood culture. Thus, variations in local blood-culture practices for young children could affect IPD incidence rates.18 In Europe, most paediatric blood isolates were obtained from children in hospital7, 10, 11, 12, 19 and are likely to show serious disease. By
IPD serogroup incidence
Figure 2A shows the absolute incidence of IPD calculated for each of the most common serogroups from young children from both western Europe and the USA. We selected studies that provided both total IPD incidence and serogroup distributions, and were derived from the same monitoring system over similar or identical periods. US serogroup data are from 3884 clinical isolates (92% invasive), obtained between 1978 and 1994,3, 20 from children younger than 6 years. European data are from: Finland
Hypothesis
We suggest that a large proportion of geographical variation in serotype distribution is attributable to differences in selection of patients and blood-culture practices. However, some true regional variations in serotype prevalence—eg, serotype 21—probably exist, especially outside the USA and Europe.
Testing the hypothesis
Direct testing of our hypothesis would require a prospective investigation of serotype monitoring and IPD rates in several countries, in which precise ages, disease manifestations, and blood-culture practices were carefully controlled and described.
Implications
Blood culture practices in different regions of the world could substantially affect the perceived coverage of multivalent pneumococcal-conjugate vaccines. The new 7-valent vaccine might prevent a greater proportion of overall IPD burden in European and Latin American children than previously thought.1 The public health and economic importance of prevention of mild IPD could depend on whether patients come into contact with a health-care system (and at what level), and if they are prescribed
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