[某医院甲型H1N1流感暴发的病例对照研究]

Chen Jian-dong, Yuan Jun, He Zheng, Yang Zhi-cong, Wang Ming

Department of Nosocomial Infection Control and Prevention, Guangzhou Center for Disease Control and Prevention, Guangzhou 510080, China.

Zhonghua Yu Fang Yi Xue Za Zhi. 2011 Feb;45(2):101-6.

OBJECTIVE

This study aimed to explore the epidemiological factors of an influenza A (H1N1) outbreak in a hospital.

METHODS

General data were collected via face-to-face interview and telephone survey. Total 132 individuals including medical and nursing staffs (37), in-patients (39) and patients' family members (56) who were exposed to the pediatric surgery ward during August 11 - 18, 2009, were investigated. The case group included 35 cases according to the diagnostic criteria for influenza A (H1N1). The other 97 persons were grouped as control. A case-control study was then conducted to explore the epidemic factors, and layering analysis was applied to determine the interactions among these factors.

RESULTS

The overall incidence in this study was 26.5% (35/132), which included 12 confirmed and 23 suspected cases, and there was no severe case. The first case was a child with the influenza-like symptoms before admission on August 11. The onsets of these cases were during August 7 - 17. The cases were distributed in 9 of 13 rooms, and there was no room aggregation in the cases distribution (χ(2) = 0.00, P > 0.05). Twelve of 25 oropharyngeal swabs were influenza A (H1N1) nucleic acid positive. The case-control study showed that exposure to the enema room accounted for 93.10% (27/29) in cases and 72.73% (48/66) in control; OR = 5.06, 95%CI = 1.01 - 34.23), long time exposure to ward was 71.43% (25/35) in cases and 44.33% (43/97) in control; OR = 3.14, 95%CI = 1.27 - 7.90), and short distance contact with the nurse LIU (76.46% (26/34) in cases and 50.52% (49/97) in control; OR = 3.18, 95%CI = 1.22 - 8.54) were the risk factors. However, keeping the window open (27.59% (8/29) in cases and 68.18% (45/66) in control; OR = 0.14, 95%CI = 0.05 - 0.39) and hand washing (25.71% (9/35) in cases and 76.29% (74/97) in control; OR = 0.11, 95%CI = 0.04 - 0.28) were the protective factors. The longer time exposure to ward had the higher risk (ratios of cases to control were 4:20 (0 - 1 day), 6:34 (2 - 4 days) and 25:43 (≥ 5 days); χ(2)(trend) = 5.737, P < 0.05). In contrast, hand washing with more frequencies (ratios of cases to control were 26:23 (0 - 1 time one day), 7:9 (2 - 3 times one day) and 2:65 (≥ 4 times one day); χ(2)(trend) = 37.136, P < 0.01) and the longer time window opening (ratios of cases to control were 21:21 (no), 4:13 (a few) and 4:32 (often); χ(2)(trend) = 13.830, P < 0.01) had the lower risk. Nevertheless, layering analysis excluded long time exposure to ward from the risk factors (for individuals with more frequent hand washing, 6.90% (2/29) exposed in cases, 7.14% (1/14) exposed in control, OR = 0.97, 95%CI = 0.06 - 29.51; for individuals keeping window open, 21.21% (7/33) exposed in cases, 8.33% (1/12) exposed in control, OR = 2.55, 95%CI = 0.26 - 60.87), indicating the main risk factors in this outbreak were exposure to the enema room and short distance contagion with the infected nurse.

CONCLUSION

The influenza A (H1N1) outbreak in this hospital was induced by an inpatient infected with influenza A (H1N1) virus before admission. Infected medical staffs keeping on work and exposure to the same place, e.g.the enema room in this study might spread the influenza A (H1N1) virus, and frequent hand washing and keeping the window open are the most effective and economic methods to prevent influenza A (H1N1) infection.

目的

本研究旨在探讨某医院甲型H1N1流感暴发的流行病学因素。

方法

通过面对面访谈和电话调查收集一般资料。对2009年8月11日至18日期间接触小儿外科病房的132人进行调查，其中包括医护人员（37人）、住院患者（39人）和患者家属（56人）。根据甲型H1N1流感诊断标准，病例组包括35例病例。另外97人作为对照组。采用病例对照研究方法探讨流行因素，并进行分层分析以确定这些因素之间的相互作用。

结果

本研究总体发病率为26.5%（35/132），其中确诊病例12例，疑似病例23例，无重症病例。首例病例为8月11日入院前出现流感样症状的儿童。这些病例的发病时间在8月7日至17日。病例分布在13个病房中的9个，病例分布无房间聚集性（χ(2)=0.00，P>0.05）。25份咽拭子中有12份甲型H1N1核酸阳性。病例对照研究显示，病例组中接触灌肠室的比例为93.10%（27/29），对照组为72.73%（48/66）；OR=5.06,95%CI=1.01 - 34.23），病例组长时间暴露于病房的比例为71.43%（25/35），对照组为44.33%（43/97）；OR=3.14,95%CI=1.27 - 7.90），与护士刘近距离接触（病例组为76.46%（26/34），对照组为50.52%（49/97）；OR=3.18,95%CI=1.22 - 8.54）是危险因素。然而，开窗通风（病例组为27.59%（8/29），对照组为68.18%（45/66）；OR=0.14,95%CI=0.05 - 0.39）和洗手（病例组为25.71%（9/35），对照组为76.29%（74/97）；OR=0.11,95%CI=0.04 - 0.28）是保护因素。暴露于病房时间越长，风险越高（病例与对照之比为4:20（0 - 1天）、6:34（2 - 4天）和25:43（≥5天）；χ(2)(趋势)=5.737，P<0.05）。相反，洗手频率越高（病例与对照之比为26:23（每天0 - 1次）、7:9（每天2 - 3次）和2:65（每天≥4次）；χ(2)(趋势)=37.136，P<0.01）和开窗时间越长（病例与对照之比为21:21（否）、4:13（偶尔）和4:32（经常）；χ(2)(趋势)=13.830，P<0.01），风险越低。然而，分层分析将长时间暴露于病房排除在危险因素之外（对于洗手频率较高的个体，病例组暴露率为6.90%（2/29），对照组为7.14%（1/14），OR=0.97,95%CI=0.06 - 29.51；对于开窗通风的个体，病例组暴露率为21.21%（7/33），对照组为8.33%（1/12），OR=2.55,95%CI=0.26 - 60.87），表明本次暴发的主要危险因素是接触灌肠室和与感染护士的近距离接触。