Longitudinal Pattern of Streptococcus Pneumoniae Nasopharyngeal Carriage and Antimicrobial Susceptibility in Healthy Children Aged Less Then 5 Years, in the Area of Milan and Surroundings, Lombardy, Italy.

The objective of this active surveillance study is to make available crucial data about epidemiology, serotype distribution, and longitudinal pattern of antibiotic susceptibility of nasopharyngeal strains of Streptococcus pneumoniae carried in the population of healthy children aged less than years and living in the area of Milan and surroundings, Lombardy, Italy. * To estimate the nasopharyngeal carriage rate and longitudinal pattern of Streptococcus pneumoniae in healthy children aged less than 5 years living in the area of Milan, Italy; * To describe the circulation of antimicrobial non-susceptible Streptococcus pneumoniae strains in healthy children aged less than 5 years Secondary objectives: * To describe the nasopharyngeal carriage distribution of Streptococcus pneumoniae strains in healthy subjects less than 5 years old; * To examine the role of risk factors in the Streptococcus pneumoniae carriage rate in healthy children; * • To evaluate the possible impact of vaccination policy in the referenced population.