Invasive pneumococcal disease in children and adults in seven Italian regions after the introduction of the conjugate vaccine, 2008-2014.

OBJECTIVE To describe the trend of invasive pneumococcal disease in the years 2008-2014; to verify the impact of the conjugate vaccine and monitor the occurrence of serotype replacement. DESIGN Prospective observational study based on data from the national surveillance for invasive bacterial diseases coordinated by the Istituto superiore di sanità. SETTING AND PARTICIPANTS Seven Italian regions (A.P. Bolzano, A.P. Trento, Emilia-Romagna, Friuli-Venezia Giulia, Lombardia, Piemonte, Veneto), accounting for 43% of the national population. MAIN OUTCOME MEASURES Number of cases and incidence of invasive pneumococcal diseases: global, stratified by age groups and by serotypes included or not in the PCV13. RESULTS In 2008-2014, in the 0-4 age group IPD incidence for all serotypes decreased from 7.1 to 2.9/100,000; incidence for vaccine serotypes (VT) decreased from 5.5 to 1.1/100,000, while incidence for non-vaccine serotypes (NVT) increased from 1.6 to 2.0/100,000 (2.5 in 2013). In the >64 age group, IPD incidence increased from 5.3 to 7.5/100,000; VT incidence decreased from 3.9 to 3.2 (4.9 in 2010 and 4.3 in 2013), whereas NVT incidence increased from 1.4 to 4.4/100,000. CONCLUSION Use of the conjugate vaccine has reduced the number of cases of IPD by VT in children; the increase in IPD by NVT, above all in older age groups, suggests a serotype replacement.