The status of invasive pneumococcal disease among children younger than 5 years of age in north-west Lombardy, Italy

Background: Streptococcus pneumoniae is a leading cause of invasive infection in young children causing morbidity and mortality. Active surveillance systems of invasive pneumococcal disease (IPD) are recommended worldwide. The aim of this study was to estimate the current incidence of IPD and to describe the serotype distribution and the antimocrobial susceptibility of S. pneumoniae isolates in children aged less than 5 years residing in North-West Lombardy, Italy. Methods: A twelve-month prospective active surveillance system recruited all children aged less than 5 years admitted for suspicion of IPD at emergency room of ten hospitals located in the monitored area. Blood samples were taken in all participants for confirmation of IPD based on isolation of S. pneumoniae from blood. Pneumococcal meningitis and sepsis were additionally confirmed by cerebrospinal fluid analysis. Serotyping and antimicrobial susceptibility testing were performed on isolates from blood. Results: A total of 15 confirmed cases of IPD were detected among 135 recruited children, including pneumonia (n = 8), bacteremia (n = 4), sepsis (n = 2) and meningitis (n = 1). The annual IPD incidence rate was 50.0/100,000 (95% CI, 30.5-82.5/100,000). Incidence was 58.3/100,000 (28.8-120.1/100,000) among children aged less than 2 years and 44.4/100,000 (22.9-87.5/100,000) among children aged 2-4 years. Thirteen isolates were typified. The most common serotype was 19A (23.1%) that together with serotypes 1, 7F and 19F accounted for 69.2% of typified isolates. Serotypes 14, 23F, 12B and 15C were also identified. The 7 and 13 valent pneumococcal conjugate vaccines covered respectively 30.8% and 84.6% of typified IPD cases. One isolate (serotype 15C) was penicillin-resistant and caused meningitis. Conclusions: The inclusion of the 13-valent pneumococcal conjugate vaccine in immunization programs of young children might be considered to reduce incidence and morbidity of invasive pneumococcal disease in this surveilled population.