目的：肺炎是小儿时期，尤其是3岁以下儿童的常见疾病，有较高的发病率和病死率。在发展中国家，病原菌以细菌感染相对多见，而病原菌的分布则随着年代不同而发生变化。该研究的目的是了解3岁以下肺炎住院患儿的深部痰液的病原学种类及分布，以期更好的指导临床用药。方法：对苏州儿童医院2006年3月至2007年1月 316 例肺炎患儿进行呼吸道深部吸痰，对其进行常见病原学检测，并分析比较。结果：316例患儿痰标本中，病原体检出率为60.8%，其中细菌检出率为51.3%，病毒总检出率为6.3%。细菌、病毒混合检出率为3.5%；细菌感染中以流感嗜血杆菌（14.6%）和肺炎链球菌（10.1%）为主；病毒感染则以呼吸道合胞病毒（4.0%）和腺病毒（3.6%）为主。结论：苏州地区3岁以下儿童的肺炎主要是由细菌感染引起的，以革兰阴性杆菌为主，流感杆菌是主要的致病菌，其次是肺炎链球菌。

OBJECTIVE: To understand the etiology of pneumonia in hospitalized patients less than 3 years of age. METHODS: A total of 316 children with pneumonia admitted to the Children's Hospital of Suzhou University in Jiangsu Province from March, 2006 to January, 2007 were enrolled in this study. Sputum samples were obtained by deep nasotracheal aspiration technique for bacterial and viral cultures. RESULTS: Of the 316 samples, specific microbial etiology was obtained in 192 cases (60.8%). Bacterial infection was found in 162 cases (51.3 %), viral infection in 19 cases (6.3%), and compound infection with virus and bacteria in 11 cases (3.5 %). Haemophilus influenzae was the most common agent (46 cases; 14.6%) in bacterial infection, followed by Streptococcus pneumoniae (32 cases; 10.1%). Respiratory syncycial virus (RSV) was the most common agent (12 cases; 4.0%) in viral infection, followed by adenovirus (11 cases; 3.6%). CONCLUSIONS: Bacterial infection was a leading cause of pneumonia in children less than 3 years of age in Suzhou area. Haemophilus influenzae was the most common agent, followed by Streptococcus pneumoniae.