Case-control study of risk factors for hospitalization caused by pandemic (H1N1) 2009

We conducted a case-control study to identify risk factors for hospitalization from pandemic (H1N1) 2009 virus infection among persons >16 years of age in Sydney, Australia. The study comprised 302 case-patients and 603 controls. In a logistic regression model, after adjusting for age and sex, risk factors for hospitalization were pregnancy (odds ratio [OR] 22.4, 95% confidence interval [CI] 9.2-54.5), immune suppression (OR 5.5, 95% CI 2.8-10.9), pre-existing lung disease (OR 6.6, 95% CI 3.8-11.6), asthma requiring regular preventive medication (OR 4.3, 95% CI 2.7-6.8), heart disease (OR 2.3, 95% CI 1.2-4.1), diabetes (OR 3.8, 95% CI 2.2-6.5), and current smoker (OR 2.0, 95% CI 1.3-3.2) or previously smoked (OR 2.0, 95% CI 1.3-3.0). Although obesity was not independently associated with hospitalization, it was associated with an increased risk of requiring mechanical ventilation. Public health messages should give greater emphasis on the risk for severe disease among pregnant women and smokers.     

甲型H1N1流感密切接触者感染危险因素的病例对照研究

目的 了解甲型H1N1流感密切接触者感染甲型H1N1流感病毒的危险因素.方法 选择2009年5月16日～9月15日在北京发现的7 099名甲型H1N1流感密切接触者作为研究对象,根据流行病学调查资料,将其中感染甲型H1N1流感病毒者纳入病例组,未感染者纳入对照组,开展病例对照研究,通过单因素和多因素非条件Logistic回归分析探寻甲型H1N1流感密切接触者感染流感的危险因素.结果 多因素分析结果显示:与＞50岁的甲型H1N1流感密切接触者相比较,20～ 50岁(OR=3.57,95％ CI:1.63～7.81)和＜20岁(OR=8.29,95％ CI:3.76 ～ 18.29)的密切接触者更有可能出现甲型H1N1流感病毒感染;与原发病例关系为家庭成员的密切接触者(OR=4.87,95％ CI:3.32 ～7.13)、暴露于症状期原发病例的密切接触者(OR=1.87,95％ CI:1.25～2.82)以及与原发病例暴露时间＞12h的密切接触者(OR=1.81,95％ CI:1.24～2.63)更易出现甲型H1N1流感病毒感染.结论 密切接触者年龄低、与原发病例关系密切、暴露于症状期的原发病例、长时间暴露于原发病例是甲型H1N1流感密切接触者发生感染的危险因素.     

Risk factors for 2009 pandemic influenza A (H1N1)-related hospitalization and death among racial/ethnic groups in New Mexico

Objectives. We assessed risk factors for 2009 pandemic influenza A (H1N1)–related hospitalization, mechanical ventilation, and death among New Mexico residents.Methods. We calculated population rate ratios using Poisson regression to analyze risk factors for H1N1-related hospitalization. We performed a cross-sectional analysis of hospitalizations during September 14, 2009 through January 13, 2010, using logistic regression to assess risk factors for mechanical ventilation and death among those hospitalized.Results. During the study period, 926 laboratory-confirmed H1N1-related hospitalizations were identified. H1N1-related hospitalization was significantly higher among American Indians (risk ratio [RR] = 2.6; 95% confidence interval [CI] = 2.2, 3.2), Blacks (RR = 1.7; 95% CI = 1.2, 2.4), and Hispanics (RR = 1.8; 95% CI = 1.5, 2.0) than it was among non-Hispanic Whites, and also was higher among persons of younger age and lower household income. Mechanical ventilation was significantly associated with age 25 years and older, obesity, and lack of or delayed antiviral treatment. Death was significantly associated with male gender, cancer during the previous 12 months, and liver disorder.Conclusions. This analysis supports recent national efforts to include American Indian/Alaska Native race as a group at high risk for complications of influenza with respect to vaccination and antiviral treatment recommendations.Rates of 2009 pandemic influenza A (H1N1)–related hospitalization and death in Arizona and New Mexico have been reported to be higher among American Indians/Alaska Natives (AIANs) than among non-AIAN populations.¹ An investigation in 12 states, comprising 50% of the country''s AIAN population, reported that death rates among AIANs were 4 times higher than among non-AIANs.¹ Other studies have reported similar patterns of higher pandemic H1N1–related hospitalization and death among other indigenous populations compared with nonindigenous populations.^2–4 Health outcome differences by race/ethnicity are not fully understood but might be explained by the prevalence of underlying chronic medical conditions, access to medical care, and socioeconomic status (SES).^5,6The New Mexico Department of Health (NMDOH) began conducting statewide active surveillance of pandemic H1N1–related hospitalizations and deaths in September 2009. Statewide surveillance in New Mexico includes data primarily from 3 major racial/ethnic groups: American Indians (AIs), Hispanic Whites, and non-Hispanic Whites. In New Mexico, varied socioeconomic, cultural, and geographic factors exist that might influence access to medical care and health outcomes identified through surveillance. Given that most individuals with H1N1 illness are not hospitalized, the true denominator of H1N1 disease is difficult to determine; we therefore focused on severe illness. Specifically, we conducted this analysis to assess risk factors, including race/ethnicity, for increased pandemic H1N1–related hospitalization, mechanical ventilation, and death among New Mexico residents.     

Genetic factors in severe cases of (H1N1) 2009 influenza

The pandemic influenza (H1N1) 2009 raised a number of issues, of which we address the following: Why did between 25 and 30% of severe influenza cases show no obvious risk factor? We hypothesize that an element that can contribute to the answer are host genetic risk factors involved in poor disease progression. Several indications led us to this hypothesis: i) studies of familial aggregation in Iceland and Utah Mormons show some heritability of influenza mortality; ii) nearly 300 known human genes are necessary for the replication of the influenza virus, and iii) the most severe cases of influenza A (H1N1) 2009 showed a deregulation of the adaptive immune system. We are addressing this problem through a case-control design (hospitalized cases of influenza (H1N1) 2009 confirmed against outpatient cases, also confirmed for (H1N1) 2009), which will be genotyped for more than a million single nucleotide polymorphisms (SNPs) and copy number variations (CNVs).     

Risk of convulsions in children after monovalent H1N1 (2009) and trivalent influenza vaccines: a database study

The monovalent H1N1 (2009) pandemic influenza vaccine used predominantly in the UK in 2009/10 was a split virion vaccine with a novel oil-in-water adjuvant (ASO3). While this was highly immunogenic it was also reactogenic especially for fever in children. There is a paucity of comparative data on reactogenicity of trivalent influenza vaccine (TIV). Using the General Practice Research Database (GPRD) we investigated whether there was an increased risk of convulsions in children vaccinated with monovalent H1N1 influenza vaccine in the 2009/10 season and also the risk after vaccination with the seasonal TIVs using the self-controlled case-series method. A total of 2366 children aged under 10 years with at least one convulsion recorded in the GPRD and who had received at least one influenza vaccine at anytime (2858 doses of TIV and 1895 doses of the monovalent H1N1 influenza vaccine) were identified between May 2000 and April 2010. Over this period these 2366 children had a total of 3846 convulsion episodes. There was no increase in the incidence rate ratio (IRR) in the week after vaccination for either the monovalent H1N1 influenza vaccine (IRR 0.99, 95% CI 0.61-1.60) or the first dose of TIV (IRR 0.89, 95% CI 0.53-1.52). A signal of an elevated risk in the first few days after the second dose of monovalent H1N1 influenza vaccine was seen with an IRR for days 1-3 post vaccination of 3.48 (95% CI 0.86-14.07). This is consistent with findings of increased fever in a clinical trial. These results neither provide evidence of an increased risk of convulsions following TIV over a 10-year surveillance period nor following a single dose of the ASO3 adjuvanted monovalent H1N1 vaccine in 2009/10.     

影响医务人员感染甲型H1N1流行性感冒因素的病例-对照研究

目的 探讨影响医务人员感染甲型H1N1流行性感冒(简称流感)的因素.方法 搜集2009年8月30日至2010年1月31日北京市公立医院中医务人员甲型H1N1流感确诊病例.按1:4配对的病例-对照研究设计,在医院内分别选择感染过和未感染过甲型H1N1流感的医务人员做为病例组(54例)和对照组(216名).通过问卷调查,收集其工作和家庭卫生信息.运用条件logistic回归分析医务人员感染甲型H1N1流感的影响因素.结果 研究对象年龄为(29.6±7.4)岁,其中男性占17.4%(47/270).病例组和对照组医务人员中,分别有3例(5.6%)和74名(34.3%)接种了甲型H1N1流感疫苗,10例(18.5%)和88名(40.1%)在甲流期间使用了防护级别更高的口罩,33例(61.1%)和161名(74.5%)延长了戴口罩的时间,13例(24.1%)和85名(39.4%)使用一次性纸巾擦手,24例(44.4%)和46名(21.3%)认为根据以往经验自己比他人更易患呼吸道传染病.单因素条件logistic回归分析显示使用一次性纸巾擦手(OR=0.15,95%CI=0.04～0.57)、延长戴口罩的时间(OR=0.43,95%CI=0.20～0.92)、使用防护级别更高的口罩(OR=0.26,95%CI=0.11～0.58)、接种甲型H1N1流感疫苗(OR=0.04,95%CI=0.01～0.32)、据以往经验自己比别人更易患呼吸道传染病(OR=2.85,95%CI=1.44～5.62)等与感染甲型H1N1流感有关.多因素条件logistic回归分析结果表明,甲型H1N1流感疫苗接种史(OR=0.18,95%CI=0.06～0.51)、使用防护级别更高的口罩(OR=0.05,95%CI=0.01～0.35)、据以往经验自己比别人更易患呼吸道传染病(OR=3.69,95%CI=1.58～8.63)等3个因素与感染甲型H1N1流感有关.结论 接种甲型H1N1流感疫苗、疾病流行期间使用更高防护级别的口罩、提高自身对呼吸道疾病的抵抗能力等措施是医务人员预防甲型H1N1流感的重要手段.     

2009年上海市甲型H1N1流感疫苗大规模人群接种免疫学效果评价

目的评价2009-2010年上海市甲型H1N1流行性感冒疫苗(甲流疫苗)的免疫学效果。方法以公安人员、中小学生、医务人员这三类重点人群作为免疫学评价的对象,采用分层抽样的方法在上海市4个区县抽取公安人员110人,中小学生146人,医务人员306人,于甲流疫苗接种前和接种后5~6周分别采集外周静脉血,检测甲型H1N1流感(甲流)抗体水平,进行甲流疫苗免疫学效果评价。结果总体上,甲流抗体阳性率由接种前34.9%提高到98.9%,抗体几何平均滴度(GMT)由接种前1∶17提高到1∶351,抗体≥4倍增长率为85.6%。结论 2009年上海市大规模人群接种的甲流疫苗具有良好的免疫学效果。     

一起寄宿制学校甲型H1N1流感暴发危险因素分析

目的探讨一起甲型H1N1流感在寄宿制学校暴发的危险因素,为制定甲型H1N1流感疫情的防控措施提供科学依据。方法采用RT-PCR方法以及血凝抑制试验,进行甲型H1N1流感病毒核酸及血清抗体检测;同时进行面对问卷调查并查阅校医门诊记录,运用病例对照研究,分析甲型H1N1流感病毒感染的危险因素。结果一次疫情暴发后,学生甲型H1N1流感感染率为32.69%。2χ检验表明,同班同学发热(OR=2.257,95% CI=1.664~3.060)、同宿舍室友发热(OR=2.270,95%CI=1.782~2.891)、宿舍每天开排气扇(OR=0.776,95% CI=0.617~0.976)、宿舍朝向与当时季节风向不一致(OR=1.417,95%CI=1.114~1.801)均与甲型H1N1流感感染有关。结论加强晨检、及时发现传染源并采取单间隔离或居家隔离是控制甲型H1N1流感暴发疫情的重要手段,加强居室通风是切实可行的预防措施。     

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.     

Analysis of the effectiveness of interventions used during the 2009 A/H1N1 influenza pandemic

Background  

Following the emergence of the A/H1N1 2009 influenza pandemic, public health interventions were activated to lessen its potential impact. Computer modelling and simulation can be used to determine the potential effectiveness of the social distancing and antiviral drug therapy interventions that were used at the early stages of the pandemic, providing guidance to public health policy makers as to intervention strategies in future pandemics involving a highly pathogenic influenza strain.     

Effectiveness of the monovalent influenza A(H1N1)2009 vaccine in Navarre, Spain, 2009-2010: cohort and case-control study

We defined a population-based cohort (596,755 subjects) in Navarre, Spain, using electronic records from physicians, to evaluate the effectiveness of the monovalent A(H1N1)2009 vaccine in preventing influenza in the 2009-2010 pandemic season. During the 9-week period of vaccine availability and circulation of the A(H1N1)2009 virus, 4608 cases of medically attended influenza-like illness (MA-ILI) were registered (46 per 1000 person-years). After adjustment for sociodemographic covariables, outpatient visits and major chronic conditions, vaccination was associated with a 32% (95% CI: 8-50%) reduction in the overall incidence of MA-ILI. In a test negative case-control analysis nested in the cohort, swabs from 633 patients were included, and 123 were confirmed for A(H1N1)2009 influenza. No confirmed case had received A(H1N1)2009 vaccine versus 9.6% of controls (p<0.001). The vaccine effectiveness in preventing laboratory-confirmed influenza was 89% (95% CI: 36-100%) after adjusting for age, health care setting, major chronic conditions and period. Pandemic vaccine was effective in preventing MA-ILI and confirmed cases of influenza A(H1N1)2009 in the 2009-2010 season.     

The 2009 influenza A (H1N1) pandemic

Prior to 2009, The Netherlands had prepared itself extensively for a potential pandemic. Multidisciplinary guidelines had been drafted to control transmission and limit adverse outcomes for both a phase of early incidental introduction and for a phase with widespread transmission. The Ministry of Health had ensured a supply and distribution schedule for antivirals and negotiated a contract for vaccine purchases. During the pandemic, existing surveillance was expanded, the established infectious disease response structure was activated, and the previously prepared protocols for communication, diagnostics, use of antivirals, and vaccination implementation were operationalized and implemented. When the pandemic turned out to be less severe than many had anticipated, risk communication and rapid modification of guidelines and communication became a major challenge. Antivirals and pandemic vaccines were reserved for those at high risk for severe outcomes only. Overall, the impact of the pandemic was comparable to the impact of an average seasonal influenza epidemic, but with a shift in (severe) outcomes from the very young and elderly toward young adults. Established prepared protocols enabled timely coordinated responses. In preparing for the worst, sufficient attention must be given to preparing for a mild scenario as well.     

社区甲型流感临床特征分析与比较

目的分析和比较社区散发新型甲型H1N1流感和季节性流感临床特征,为临床诊治甲型流感提供参考依据。方法回顾性分析2009年5-10月来医院发热门诊就诊的具有流感样症状的患者,均经实时荧光定量PCR检测。结果在确诊的129例甲型流感患者中,新型甲型H1N1流感65例,占50.4%,季节性甲型流感64例,占49.6%;新型甲型H1N1流感组平均年龄21岁,季节性甲型流感组36岁,两组差异有统计学意义(P<0.01);新型甲型H1N1流感组学生占47例,占72.3%,季节性甲型流感组13例,占20.3%,两组差异有统计学意义(P<0.01);从临床表现比较,除流涕、扁桃体肿大,两组差异有统计学意义(均P<0.01)外;其他差异均无统计学意义。结论医院确诊的甲型流感患者均为轻型;新型甲型H1N1流感以年轻学生为主;两组甲型流感临床特征相似,需经PCR检测确诊分型。     

北京市2009年甲型H 1N 1流感防控效果定量评价

目的 定量评价北京市甲型H1N1流感的防控措施效果,为制定和调整传染病防控策略提供依据.方法 利用北京市2009年甲型H1N1流感流行病学数据,基于传染病传播动力学机制,考虑了甲型H1N1流感的季节性,并引入疫苗接种量,建立定量评价甲型H1N1流感防控效果的数学模型.结果 2009年北京市甲型H1N1流感的平均潜伏期约为1.82 d,平均感染期约为2.08 d, 前中后三期有效再生数分别为1.13、1.65 和 0.96;北京市采取了一系列甲型H1N1 流感防控措施使2009年甲型H1N1流感报告的实际病例数远远小于其自然状态下的累计例数;接种甲型H1N1流感疫苗使2009年累计病例数减少24.08%,且使发病高峰时间推后.结论 北京市采取的一系甲型H1N1流感防控措施整体上显著有效,接种甲型H1N1流感疫苗不仅降低了疫情规模, 还能延迟疫情达到高峰的时间 .     

Distribution and risk factors of 2009 pandemic influenza A (H1N1) in mainland China

Data from all reported cases of 2009 pandemic influenza A (H1N1) were obtained from the China Information System for Disease Control and Prevention. The spatiotemporal distribution patterns of cases were characterized through spatial analysis. The impact of travel-related risk factors on invasion of the disease was analyzed using survival analysis, and climatic factors related to local transmission were identified using multilevel Poisson regression, both at the county level. The results showed that the epidemic spanned a large geographic area, with the most affected areas being in western China. Significant differences in incidence were found among age groups, with incidences peaking in school-age children. Overall, the epidemic spread from southeast to northwest. Proximity to airports and being intersected by national highways or freeways but not railways were variables associated with the presence of the disease in a county. Lower temperature and lower relative humidity were the climatic factors facilitating local transmission after correction for the effects of school summer vacation and public holidays, as well as population density and the density of medical facilities. These findings indicate that interventions focused on domestic travel, population density, and climatic factors could play a role in mitigating the public health impact of future influenza pandemics.