Invasive pneumococcal disease in children: geographic and temporal variations in incidence and serotype distribution

We examined published studies from the United States, Europe, and Latin America to better understand geographic and temporal variability in the epidemiology of invasive pneumococcal disease (IPD) in young children. A comparison of IPD incidence levels reported for children < 5 years of age within the United States (CDC) surveillance system over the past 5 years revealed little variation over that time period. Within the Danish national surveillance system, a 3-4 fold increase in bacteremic IPD in that age group was reported over the past 15 years. Nonetheless, the United States IPD incidence remains 4-8 fold higher than that reported for Denmark or other Western European countries. A retrospective analysis at one North American hospital spanning 40 years indicated that the seven serogroups represented in the licensed pneumococcal conjugate vaccine (4, 6, 9, 14, 18, 19, 23) consistently comprised 80%-90% of all serogroups causing IPD in young children. More recent retrospective comparisons in Spain, the United Kingdom, France, Belgium, and Denmark suggest modest increases in vaccine serogroup coverage over the past 10-20 years. However, in European children vaccine serogroups consistently account for 10%-20% less of the overall IPD burden as compared to North American children. Conclusion: factors that likely underlie a significant proportion of these apparent temporal and geographic differences include variability in blood culturing rates, in antibiotic resistance levels, and in the precise age distributions of the populations studied.