目的 分析极低/超低出生体重（VLBW/ELBW）早产儿晚发败血症（LOS）的临床特征及病原菌情况。方法 在2012年1月至2016年12月收治的VLBW/ELBW早产儿（胎龄<32周）中，选取发生LOS的患儿作为LOS组，每例LOS患儿匹配2例非败血症患儿作为对照组。根据是否发生院内死亡，将LOS组分为死亡亚组和存活亚组，分析LOS发生的危险因素、临床特征、病原菌分布、耐药情况及死亡危险因素。结果 共收治VLBW/ELBW早产儿513例，LOS组65例，对照组130例，LOS发生率为12.7%。LOS组死亡6例，存活59例。LOS组出生体重低于对照组（P < 0.05），LOS组经外周静脉穿刺中心静脉置管（PICC）时间、机械通气时间、住院时间长于对照组（P < 0.05）。LOS组小于胎龄儿（SGA）、机械通气、新生儿坏死性小肠结肠炎、死亡比例高于对照组（P < 0.05）。低出生体重、SGA、PICC时间长为VLBW/ELBW早产儿发生LOS的危险因素（分别OR=1.396、2.550、1.068，P < 0.05）。合并化脓性脑膜炎是VLBW/ELBW早产儿LOS死亡的危险因素（OR=13.443，P < 0.05）。LOS组共培养出65株病原菌，39株（60%）为革兰阴性菌，其中15株为产超广谱β-内酰胺酶（ESBLs）菌，67%（10/15）感染ESBLs菌的LOS患儿发病2周前应用过抗生素，高于非耐药菌（29%，7/24）（P < 0.05）。结论 出生体重低、SGA、PICC时间长为VLBW/ELBW早产儿发生LOS的危险因素，合并化脓性脑膜炎的LOS患儿更容易发生死亡。LOS病原菌以革兰阴性菌多见，发病2周前应用过抗生素可能会增加ESBLs菌感染。

Objective To study the clinical features and pathogenic bacteria of late-onset sepsis (LOS) in very low birth weight (VLBW) and extremely low birth weight (ELBW) infants. Methods Among the VLBW/ELBW infants with a gestational age of < 32 weeks who were admitted to the hospital between January 2012 and December 2016, those with LOS were enrolled as the LOS group, and those without sepsis were matched for the infant with LOS in gestational age were enrolled as the control group. According to the presence or absence of in-hospital death, the LOS group was further divided into a death subgroup and a survival subgroup. Risk factors for LOS, clinical features, distribution of pathogenic bacteria, drug resistance, and high-risk factors for LOS-related death were analyzed. Results A total of 513 VLBW/ELBW infants were enrolled, and there were 65 infants in the LOS group and 130 in the control group. The incidence rate of LOS was 12.7%. In the LOS group, 6 infants died and 59 survived. Compared with the control group, the LOS group had a significantly lower birth weight (P < 0.05) and significantly longer indwelling time of peripherally inserted central catheter (PICC), duration of mechanical ventilation, and length of hospital stay (P < 0.05). Compared with the control group, the LOS group had a significantly higher proportion of small-for-gestational-age infants, infants undergoing mechanical ventilation, infants with neonatal necrotizing enterocolitis, or infants who died (P < 0.05). Low birth weight, small-for-gestational-age infant, and long indwelling time of PICC were independent risk factors for LOS in VLBW/ELBW infants (OR=1.396, 2.550, and 1.068 respectively, P < 0.05). Purulent meningitis was an independent risk factor for LOS-related death in VLBW/ELBWIs infants (OR=13.443, P < 0.05). A total of 65 strains of pathogenic bacteria were cultured in the LOS group, among which there were 39 strains (60%) of Gram-negative bacteria, including 15 strains producing extended spectrum beta-lactamases (ESBLs), and antibiotics were applied for 67% (10/15) of the ESBL strains within 2 weeks before the onset of LOS. The rate of antibiotic use for ESBL strains was significantly higher than that for non-resistant strains[67% (10/15) vs 29% (7/24); P < 0.05]. Conclusions Low birth weight, SGA infant, and long indwelling time of PICC are independent risk factors for LOS in VLBW/ELBW infants, and death tends to occur in LOS infants with purulent meningitis. Most pathogenic bacteria of LOS are Gram-negative bacteria, and use of antibiotics within 2 weeks before disease onset may increase the risk of ESBL strain infection.