Elsevier

The Lancet

Volume 357, Issue 9260, 24 March 2001, Pages 950-952
The Lancet

Hypothesis
Geographical differences in invasive pneumococcal disease rates and serotype frequency in young children

https://doi.org/10.1016/S0140-6736(00)04222-7Get rights and content

Summary

The development of glycoconjugate vaccines for Streptococcus pneumoniae that are effective in very young children has renewed interest in identification of which among the more than 90 pneumococcal serotypes are most likely to cause invasive pneumococcal disease (IPD). Serotype distribution is thought to vary geographically, even between regions as socio economically similar as western Europe and North America. To explain these variations, we note the considerable variation that exists between reported rates of IPD in young children in the USA and west European countries. We postulate that this variation is attributable to different blood-culture rates and practices, and that mild IPD is probably underdiagnosed and under-reported in western Europe. On the basis of a comparison of serotype distributions between the two regions, we also postulate that those serotypes found at similar frequencies in both regions are virulent and rarely cause mild disease. As a result, reported distributions of IPD serotypes, especially when expressed as percentages, might be strongly skewed by the distribution of clinical presentations in a particular study population.

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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