一起医院内甲型H1N1流行性感冒暴发原因的病例-对照研究

目的 了解影响甲型H1N1流行性感冒(简称流感)医院内暴发的流行病学因素. 方法 主要采用面对面访谈和电话问答方式,调查2009年8月11-18日暴露于小儿外科的39名住院患者、56名陪护家属及37名医务人员(共132名),将符合甲型H1N1流感诊断定义的35例罹患流感者纳入患者组,余97名对象纳入对照组,采用病例-对照研究方法探讨影响疫情暴发的因素,应用分层分析方法检测因素间的交互作用. 结果 调查发现人群总罹患率为26.5%(35/132),患者组中12例为确诊患者,23例为疑似患者,无重症患者.首例患者为一住院患儿,8月11日入住小儿外科前已有流感样症状.35例患者发病时间为8月7-17日.患者分布在13间病房的9间里,患者分布无房间聚集性(x2=0.00,P＞0.05).25份咽拭子标本检出12例甲型H1N1流感病毒核酸阳性.病例-对照研究结果表明灌肠室暴露[病例组暴露率93.10%(27/29),对照组暴露率72.73%(48/66),OR=5.06,95%CI=1.01～34.23]、长时间暴露于病区[病例组暴露率71.43%(25/35),对照组暴露率44.33%(43/97),OR=3.14,95%CI=1.27～7.90]和近距离接触刘护士[病例组暴露率76.46%(26/34),对照组暴露率50.52%(49/97),OR=3.18,95%CI=1.22～8.54]是危险因素.而长时间开窗[病例组暴露率27.59%(8/29),对照组暴露率68.18%(45/66),OR=0.14,95%CI=0.05～0.39]和勤洗手[病例组暴露率25.71%(9/35),对照组暴露率76.29%(74/97),OR=0.11,95%CI=0.04～0.28]是保护因素.同时病区暴露时间越长风险越大(暴露时间0～、2～和5～d的人群,患者与非患者的比分别是4:20、6:34和25:43,x2趋势=5.737,P＜0.05),而每天洗手频率越多(洗于次数0～、2～和4～次的人群,患者与非患者的比分别是26:23、7:9和2:65,x2趋势=37.136,P＜0.01)、开窗时间越长(开窗频率为不开、一会和大半天的人群,患者与非患者的比分别是21:21、4:13和4:32,x2趋势=13.830,P＜0.01)则患病风险越小.但是,利用分层分析发现病区暴露时间长并不是危险因素[在勤洗手人群中,病例组暴露率6.90%(2/29),对照组暴露率7.14%(1/14),OR=0.97,95%CI=0.06～29.51;在长时间开窗的人群中,病例组暴露率21.21%(7/33),对照组暴露率8.33%(1/12),OR=2.55,95%CI=0.26～60.87].因此,此次甲型H1N1流感暴发的危险因素主要是灌肠室暴露与近距离接触患病医护人员. 结论 院外甲型H1N1流感患儿入住小儿外科病区导致本次甲型H1N1流感院内感染,患病坚持在岗的医护人员或灌肠室等共同暴露导致病毒传播;而勤洗手和长时间开窗是预防甲型H1N1流感感染的经济有效的方法.

Abstract：

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 (x2=0.00,P＞0.05).Twelve of 25 oropharyngeal swabs were influenza A (H1N1) nucleic acid positive.The casecontrol 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(2-4days) and 25:43 (≥5 days)x2trend = 5.737,P ＜ 0.05).In contrast,hand washing with more frequeucies (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) ;x2trend =37.136,P ＜0.01) and the longer time window opening (ratios of cases to control were21:21 (no),4:13 (a few) and 4:32 (often);x2trend= 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 (H1 N1) infection.

A case-control study of an influenza A (H1N1) outbreak in a hospital

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 (x2=0.00,P＞0.05).Twelve of 25 oropharyngeal swabs were influenza A (H1N1) nucleic acid positive.The casecontrol 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(2-4days) and 25:43 (≥5 days)x2trend = 5.737,P ＜ 0.05).In contrast,hand washing with more frequeucies (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) ;x2trend =37.136,P ＜0.01) and the longer time window opening (ratios of cases to control were21:21 (no),4:13 (a few) and 4:32 (often);x2trend= 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 (H1 N1) infection.