Trends in invasive pneumococcal disease among older adults in Olmsted County, Minnesota

SummaryObjectiveFollowing the introduction of a 7-valent pneumococcal conjugate vaccine (PCV-7) for children in early 2000 in the United States, a decrease in the incidence of invasive pneumococcal disease (IPD) was seen in adults, likely due to a herd effect. However, there have been recent increases in IPD in adults caused by Streptococcus pneumoniae serotypes not included in PCV-7, so called “replacement disease”. We performed a population-based study to further investigate this emerging concern.MethodsPopulation-based incidence study in Olmsted County, Minnesota, United States, in adults aged ≥50 years.ResultsFrom 1/1/1995 to 12/31/2007, 104 cases of IPD were identified in Olmsted County in adults aged ≥50 years. We found a 45% increase in the incidence rate of IPD from 2001–2003 (17.7 cases per 100,000 person-years) to 2004–2007 (32.1 cases per 100,000 person-years) (p = 0.029). From 2002–2004 to 2005–2007, the incidence rate of IPD caused by S. pneumoniae serotypes not included in PCV-7 increased from 9.2 to 32.8 cases per 100,000 person-years (p < 0.001).ConclusionA recent increase in the incidence of IPD in adults aged ≥50 years was demonstrated in Olmsted County, Minnesota due to serotypes not found in PCV-7. These findings are unique and merit further investigation.