Characteristics of Invasive Pneumococcal Disease in Young Children before the Introduction of PCV13 in Lombardy, Italy

An active surveillance system of invasive pneumococcal disease (IPD) started on September 2008 in Lombardy, Italy, among children aged less than 60 months and admitted for suspicion of IPD at emergency room of ten hospitals. This study examined the clinical characteristics of children enrolled up to December 2010, that is just before the introduction in this region of voluntary mass vaccination, free of charge, based on the 13-valent pneumococcal conjugate vaccine (PCV13). Two hundred fifty one children were suspected and 20 were confirmed as having IPD, based on isolation of Streptococcus pneumoniae from blood. Thirty-nine percent of children had received pneumococcal vaccination previously, and full vaccination with three doses of hepta-valent vaccine (PCV7) had been administered in 21.4%. Co-morbidity conditions were more frequent in children with confirmed than non-confirmed IPD (10.0% vs. 0.9%). The annual incidence rate of confirmed IPD was 28.6/100,000 (binomial 95% confidence interval, 18.6 to 44.1/100,000. Among confirmed IPD children, 11 exhibited pneumonia with bacteremia, 6 bacteremia without focus, 2 septicemia, 1 meningitis. Seventeen (85%) isolates were identified, and nine serotypes. The overall serotype coverage was 29.4% for PCV7 and 82.3% for PCV13. In non-vaccinated children, the coverage of PCV7 and PCV13 was 41.7% and 75.0%, respectively. Non-vaccine serotypes 12B, 15C, and 23B were identified. Antibiotic resistance was found in seven children, that is against penicillin (serotype 15C), erythromycin (14, 19A, 19F), tetracycline (15C, 19F), chloramphenicol (23F), and trimethoprim-sulfamethoxazole (23F). Two of these children had received antibiotic therapy (penicillin or azithromycin) during the week before hospital admission. The coverage vaccination rate in Lombardy was relatively low during the surveillance period and serotype distribution widespread. The introduction of PCV13 and a mass vaccination program in young children might impact positively on invasive pneumococcal disease in this surveilled population. Active long-term surveillance of non-vaccine serotypes is required wordwide.