This study is to observe the carriage rate of Streptococcus pneumoniae (S.p.), Haemophilus influenzae Type B (Hib) and Moraxella catarrhalis (M.Cat.) in healthy Chinese children aged 12-18 months in order to estimate the prevalence of pathogens that commonly cause infection in Chinese young children. The antibiotic resistance of all isolates and the serotypes distribution of S.p. isolates will also be tested. Potential risk factors for nasopharyngeal carriage will be collected.