Objective: To investigate the clinical characteristics of respiratory syncytial virus(RSV)bronchiolitis and molecular biological characteristics of RSV in children in Beijing. Method: In a systematic retrospective study, 2 296 nasopharyngeal aspirates (NPA) were collected from children diagnosed with bronchiolitis from July 2006 to June 2016 for respiratory virus screening using direct immunofluorescence assay (DFA). For specimens positive for RSV, subgroup A or B was confirmed by real time RT-PCR and genotype of RSV was determined by amplifying the full G glycoprotein gene and sequencing. Clinical data were evaluated by the modified Tal score to compare the severity between RSV subtypes, as well as genotypes. Statistical analyses were performed using t test, Mann-Whitney U test and χ² test. Result: In 2 296 bronchiolitis cases, 961(41.9%) were RSV positive, including 719(74.8%) RSV A and 236 (24.6%) RSV B. The dominant RSV subtype changed from year to year: A-A-B-B-A-A-B-AB-A-AB and more bronchiolitis cases were identified in RSV A dominant years. Six genotypes of RSV A (NA1, NA2, NA3, NA4, GA5 and ON1) and 5 genotypes of RSV B (BA3, BA7, BA9, BA10 and CB1) were prevalent in Beijing. The dominant genotypes of RSV A were NA1 (55.9%) with high rates (50.0%-100%) before 2014 and ON1 (39.1%), mainly detected after 2014, while BA9 (90.6%) was the absolute dominant RSV B genotype. No significant difference in the severity of bronchiolitis was shown between cases of RSV A and B. Children positive for NA1 were more likely to stay longer in hospital (Median time: 8 days) compared to the group positive for ON1(Median time: 6 days ) (U=1.035, P=0.005) and had higher proportion of moderate to severe degree symptoms (Moderate: 41.0%, Severe: 10.0%) compared with ON1 group (Moderate: 22.9%, Severe: 4.3%) (U=9.785, P=0.008). In the group positive for ON1, more children had fever (ON1: 38.6%, NA1: 15.0%) (χ²=11.064, P=0.001) and more were younger than 3 months(ON1: 54.3%, NA1: 33.0%) (χ²=77.408, P<0.001). Conclusion The dominant RSV subgroup changed from year to year with a shifting pattern. The correlation between RSV genotypes and the severity of disease was documented in the study.

AIM: Through the Monte Carlo simulation to monitor the change of MIC in late-onset sepsis of gram-positive cocci in neonates, through the cumulative fraction of response to evaluate the changing trend of bacterial resistance in our center and analyze the possibility of inducing drug resistance of bacterial, to reduce the occurrence of bacterial drug resistance in clinical work. METHODS: This study retrospectively investigated the basic information, pathogen species and drug sensitivity results of neonatal late-onset sepsis of gram-positive cocci in Neonatal Intensive Care Units of Beijing Maternity Hospital from 2016 to 2019, and divided them into four groups by year. Crystal ball software was used to calculate the annual CFR of sensitive antibiotics (Vancomycin) against the gram-positive cocci by Monte Carlo simulation. RESULTS: From 2016 to 2019, there were 58 cases of late-onset sepsis caused by gram-positive cocci in neonates, and the number of pathogens detected each year showed no significant change, and there was no statistical difference in the affected population each year. Among them, the top three were 31 strains of Staphylococcus epidermidis (53.5%), 9 strains of Enterococcus faecium (15.5%), and 6 strains of Enterococcus faecalis (10.3%). Drug sensitivity tests showed that the resistance rates of Staphylococcus epidermidis, Enterococcus faecium and Enterococcus faecalis to Vancomycin and Linezolid were 0%. The CFR of Vancomycin against gram-positive cocci from 2016 to 2019 calculated by Monte Carlo simulation were 82%, 88.72%, 81.73% and 78.53%, respectively, which showed a downward trend. CONCLUSION: By using Monte Carlo simulation method, CFR can reflect the change of bacterial drug resistance with drug sensitivity test as the standard, and evaluate the current treatment plan, which should be paid attention to in clinical work.