Abstract: Background：Chinese Infectious Disease Surveillance of Pediatrics(ISPED)was established in 2015. The data of antibiotics resistance were collected from each hospital and summarized every year to monitor the infectious etiology changes and bacterial drug resistance among Chinese children. Objective：This study is aimed to investigate the bacterial infectious and antimicrobial resistance profiles of pathogens in Chinese children and guide the reasonable use of antibiotics. Design：A crosssectional survey. Methods：Clinical isolates were collected from 13 tertiary children hospitals in China from January 1st to December 31st in 2021. Antimicrobial susceptibility testing was carried out according to a unified protocol using KirbyBauer method or automated systems. Penicillin susceptibility of streptococcus pneumonia was detected by Etest. All of the antimicrobial susceptibility testing results were interpreted according to the criteria of Clinical and Laboratory Standards Institute (CLSI) 2021. All members used the standard methods to perform bacterial culture,identification and antimicrobial susceptibility test and reported the isolated effective strains and bacterial resistance data in a structured format every year for data summary and statistical analysis. Main outcome measures：Detect the distribution of bacteria strains in children and the changes of bacteria drug resistance. Results：A total of 63 508 isolates were collected, of which 39.9% was grampositive organisms and 60.1% was gramnegative organisms. Top ten pathogens were as follows, Escherichia coli (12.7%), Streptococcus pneumonia (12.3%), Straphylococcus aureus (11.6%), Haemophilus influenza (11.4%), Moraxella catarrhalis (6.5%), Klebsiella pneunoniae (5.2%), Pseudomonas aeruginosa (4.0%), Staphylococcus epidermidis (3.7%), Acinetobacter baumannii (2.4%) and Streptococcus pyogenes (2.1%). The distribution of the primary pathogenic bacteria in different age groups was different. Among them, Saureus had the highest isolation rate in neonates (18.7%), and S.pneumoniae was the main pathogenic bacteria in children aged from >28 d to 5 years old, arranging from 13.6% to 20.8%. E.coli was the most common pathogen in children over 5 years old (22.4%). The proportion of penicillininsensitive S.pneumoniae (PNSP) decreased to 9.6%. Multidrugresistant bacteria (MDROs) showed high levels of resistance to a variety of clinical antibiotics, and the ratios of carbapenemresistant Enterobacteriaceae (CRE), K.pneumoniae (CRKP), P.aeruginosa (CRPA), A.baumannii (CRAB) were 4.6%, 14.8%, 6.7% and 30.7%, respectively. The proportions of CRPA and CRAB showed a decreasing trend in the past 6 years. The former had a higher detection rate in the neonatal group, while the latter had a higher detection rate in the nonneonatal group. Moreover, the resistance rates of CRPA and CRAB to multiple antibiotics were significantly higher in the nonneonatal group than in the neonatal group. Methicillinresistant Saureus(MRSA) was relatively stable, with a detection rate of 33.2% in 2021. Conclusion：The detection rate of MDROs in 2021 was lower than previous years, and the resistance ratio of MDROs also decreased in pediatric patients. We must pay attention to the infection and colonization of CRPA in the neonatal population.

Key words: Bacteria, Antimicrobial resistance, Children, Infectious Disease Surveillance for Pediatrics, 2021