Modelling potential responses to severe acute respiratory syndrome in Japan: the role of initial attack size, precaution, and quarantine

BACKGROUND: There has been an outbreak of the severe acute respiratory syndrome (SARS) worldwide. With the use of detailed epidemiological data from other countries, this article describes the possible reason for the SARS epidemic not appearing in Japan, and simulates the impact of different control strategies that can break the transmission cycle of SARS associated coronavirus. METHOD: Mathematical modelling is used for predicting the epidemiological outcome and simultaneously for evaluating the effect of interventions on SARS. The study estimates the initial attack size that would result in failed invasion. Three different interventions have been incorporated into the public health response policies; precautionary public health measures, isolation of infected people, and quarantine of exposed humans. RESULTS: The maximum number of humans newly infected could be roughly estimated on the basis of the initial attack size, using simple formulas. It is seen that the introduction of only a few cases into certain communities would not lead easily to an epidemic. The possible trajectories of SARS epidemic depend on the levels of public health interventions as quarantine and precautionary public health measures greatly affected the transmissibility of the disease. It is shown that there exist threshold levels of interventions at which the SARS epidemic settles down. CONCLUSION: Initial attack size is one of the determinants of whether SARS can successfully invade the community or not. Two of the most effective policy procedures to prevent new infections would be to apply stringent precautionary measures and to impose quicker and more effective quarantine of the exposed populace.     

北京市2003年SARS疫情的多维分布及其影响因素分析

目的采用多维可视化分析研究北京市2003年严重急性呼吸综合征(SARS)疫情的扩散过程。方法以北京市SARS疫情数据,结合北京市地理信息系统,基于数据驱动和模型驱动的理论和技术,利用热点分析、空间过程分析和因子识别等数据探索分析方法,根据传染病的多维传播特性,同时利用遗传规划和模拟退火相结合的算法对易感-感染-移出(SIR)模型求解,从模型直接求取SARS流行病学参数。结果SARS密切接触者在城市内部呈现出大尺度上沿交通线聚集和在小尺度上随机分布态势;在不同发展阶段,北京市SARS发病趋势存在显著的空间聚集和扩散变化特征;地理位置、人口以及医院和医生数量是SARS空间传播的重要影响因子;通过对SIR模型直接求解,反演传染病参数,对SARS确诊病例数可进行早期预报性分析。结论对SARS密切接触者的集聚探测揭示了北京市人群存在两个空间尺度上的流动接触过程,为人-人接触性传染病的预防和控制策略制定提供重要依据;多个环境和人文因子对SARS传播起作用,其统计显著性随时间变化;有效的算法可以对SIR直接求解,使其可以用于传染病参数反演和早期预测。     

应用系统动力学模型对SARS疫情传播及主要防控措施效果的计算机模拟仿真研究

目的　(1)应用系统动力学方法建立数学模型,宏观地模拟严重急性呼吸综合征(SARS)疫情在自然人群和医院内传播的过程,以及患者通过就诊和社区隔离措施移出传播链的过程。(2)通过计算机对该模型的仿真模拟,分析在突发 SARS疫情的情况下,代表主要防控措施的变量对疫情曲线的影响模式和相对强度。(3)重点分析发热监测措施对疫情的影响,根据分析结果对今后SARS防控工作提出政策建议。方法　采用面访、问卷调查、文献检索、个案分析等方式,获取SARS传播的重要参数。应用系统动力学理论及计算机仿真系统建立数学模型,并进行 What if仿真分析。结果　建立了能够反映SARS自然传播、患者就诊及医院内传播、社区隔离措施、发热监测过程的计算机仿真模型,通过宏观模拟SARS患者从发病到被移出传播链的过程得出下列结果:(1)患者从发病到就诊的时间、患者每日平均接触人数、就诊时医院内接触人数等是对 SARS的院内、院外传播过程影响最大的几个变量;(2)隔离强度、接诊医生对 SARS的警惕性、医院通风消毒、医院优化患者流动路线、医生防护强度是影响疫情控制的主要变量;(3)医院入口的体温筛查措施对疫情控制的作用不大。结论　按照目前制定的SARS防治预案,卫生系统能够快速控制突发的SARS疫情。     

Efficiency of quarantine during an epidemic of severe acute respiratory syndrome--Beijing, China, 2003

During March--July 2003, an epidemic of severe acute respiratory syndrome (SARS) in Beijing, China, accounted for 2,521 probable cases (attack rate: 19 per 100,000 population). To control the epidemic, public health officials initiated enhanced surveillance, isolation of SARS patients, use of personal protective equipment (PPE) by health-care workers, and quarantine of contacts of known SARS patients. Approximately 30,000 Beijing residents were quarantined in their homes or quarantine sites. To guide future quarantine policy, the Chinese Field Epidemiology Training Program (China FETP) of the Chinese Center for Disease Control and Prevention (China CDC) conducted a survey to estimate the risk for acquiring SARS among quarantined residents of Haidian District (2001 population: 2.24 million), Beijing, in May 2003, 1 month after the epidemic peaked. This report summarizes the results of that survey, which indicate that, as a component of a comprehensive SARS-control program, quarantine should be limited to persons who have contact with an actively ill SARS patient in the home or hospital, allowing for better focus of resources in future outbreaks.     

北京市2003年城区和郊县SARS流行情况分析

目的 了解2003年北京传染性非典型肺炎(SARS)流行的基本情况，描述城区和郊县SARS流行的基本特征。方法 应用SPSS软件对北京市疾病预防控制中心SARS疫情数据库进行分析。结果 北京市城区发病率为29．058／10万．死亡率2．213／10万，病死率为7．62％；郊县发病率为10．612／10万，死亡率0．775／10万，病死率为7．32％。城区和郊县SARS病人人口学特征基本～致。结论 北京SARS流行的特点为城市高发。     

Understanding the spatial diffusion process of severe acute respiratory syndrome in Beijing

OBJECTIVES: To measure the spatial contagion of severe acute respiratory syndrome (SARS) in Beijing and to test the different epidemic factors of the spread of SARS in different periods. METHODS: A join-count spatial statistic study was conducted and the given hypothetical processes of the spread of SARS in Beijing were tested using various definitions of 'joins'. RESULTS: The spatial statistics showed that of the six diffusion processes, the highest negative autocorrelation occurred in the doctor-number model (M-5) and the lowest negative autocorrelation was found in the population-amount model (M-3). The results also showed that in the whole 29-day research period, about hour or more days experienced a significant degree of contagion. CONCLUSIONS: Spatial analysis is helpful in understanding the spatial diffusion process of an epidemic. The geographical relationships were important during the early phase of the SARS epidemic in Beijing. The statistic based on the number of doctors was significant and more informative than that of the number of hospitals. It reveals that doctors were important in the spread of SARS in Beijing, and hospitals were not as important as doctors in the contagion period. People are the key to the spread of SARS, but the population density was more significant than the population size, although they were both important throughout the whole period.     

北京市海淀区403例传染性非典型肺炎的流行病学分析

目的　分析北京市海淀区常住人口传染性非典型肺炎 [严重急性呼吸综合征 (SARS) ]的流行病学特征。方法　对海淀区常住人口中发生的SARS病例进行个案调查和描述性分析。结果2 0 0 3年 3月 1 8日至 5月 31日 ,海淀区常住人口中共发生SARS病例 40 3例 ,发病率约为 1 8.0 1 0万 ,死亡 2 7例 ,病死率为 6 .7%。患者中青壮年占 70 .4% ,尤以 2 0～ 2 9岁组高发。全区除一个乡外均受累 ,多以散发为主 ,只有 3个街道呈现明显的家庭或学校内爆发。流行基本可以划分为初始增长期(2 7天 )、高峰期 (2 1天 )和快速下降期 (2 6天 )。患者中有密切接触史的比例随各期呈递减趋势 (趋势χ2 =8.80 0 ,P =0 .0 0 3) ;初期接触地点主要在医院 (72 .7% ) ,而迅速下降期则以家中接触为主(85 .7% ) ;各期的职业构成谱也明显不同 (χ2 =36 .41 ,P <0 .0 1 )。无明确接触史的患者中 2 6 .6 %有外出史 ,其中又有 47.6 %是去医院 ,并且 65 %在流行的高峰期光顾医院。结论　海淀区常住人口SARS流行强度与全市持平 ,医院内获得感染是SARS流行的主要原因     

Hindsight: a re-analysis of the severe acute respiratory syndrome outbreak in Beijing

OBJECTIVE: To review the severe acute respiratory syndrome (SARS) epidemic in Beijing using basic epidemiological principles omitted from the original analysis. STUDY DESIGN: Analysis of Prospective surveillance data for Beijing collected during the outbreak. METHODS: Surveillance data were reclassified according to World Health Organization criteria. Cases previously excluded without date of onset of illness were included in the epidemic curve from estimates using the average time between date of onset and date of hospitalization for cases with both dates. Cases who failed to give a contact history were now included; 7% (n=5) of cases during the import phase and 61% (n=365) during the peak phase. Previously excluded cases were included for plotting on an epidemic curve, and basic spot mapping for distribution of cases was used from attack rates recalculated for age, gender, occupation, residential location, date of onset of illness and demographics. RESULTS: The spot map effectively illustrated clusters by residency, with the inner-city sustaining the highest attack rate (33.42 per 100,000), followed by an easterly distribution 5-30km away (21.62 per 10,000), and lowest in districts 60-160km away (9.21 per 100,000). The new epidemic curve shows the outbreak commencing 10 days earlier than initially reported, with a three-fold greater increase in cases during the escalation phase than previously estimated. CONCLUSION: In hindsight, the investigation of the Beijing SARS would have benefited from the use of spot maping as an essential outbreak tool for early identification of specific geographical area(s) for quarantining. If a spot map of incidence density rates was used during the early phase of the outbreak, the inner city might have been identified as a major risk factor requiring rapid quarantining. Contact history became uncommon as the outbreak progressed, suggesting that hospitals were over-burdened or pathogenesis and environment risk factors changed, strengthening the usefulness of early spot mapping and the need to modify risk factors included as contact history as the epidemic progresses.     

天津市传染性非典型肺炎流行特点及主要控制措施效果评价

目的：分析天津市传染性非典型肺炎[严重急性呼吸综合征(SARS)]流行病学特征，对主要控制措施的效果进行初步评价。方法：采用自行设计的病例报告表，全市统一的流行病学个案调查表及病例接触者、密切接触者树状分布图，深入病房、家庭、社区、团体等对病例及接触者进行调查。结果：以发病时间计算，自2003年4月13日至5月8日，包括输入病例在内发病175例，发病率为1．9／10万，其中死亡14例，病死率达8．O％。整个流行过程不足1个月，流行特点：1例“超级传播者”直接或间接传染了全市94．3％的病例；呈现以A、B、C 3家医院聚集发病为特点的爆发性流行，占全市病例的68．6％，3家医院外的家庭聚集发病占全市病例的14．3％，同事间传播为2．3％，散发者为9．1％，这些散发者未造成接触者感染；早期医务人员发病较多，占总病例数的38．2％，流行全过程参加SARS救治工作的1975名医护人员的总感染率为3．4％；全部流行过程传染源明确，传染链清晰，全市仅3例患者未找到传染源，占病例总数的2％；在10例源头病例中仅“超级传播者”和另一病例传染了其接触者，其他传染源由于及时隔离未造成任何传播。结论：SARS是严重急性呼吸系统传染病，如能及时准确地掌握传染链并进行范围适当、及时有效的封闭及隔离措施，以科学的方法提高全民的警觉度，传染链可能在较短时间内被切断，从而控制传播。     

定量评价SARS干预措施效果的传播动力学模型

目的建立一种可以用于严重急性呼吸综合征(SARS)干预措施效果定量评价的传播动力学模型。方法根据SARS流行规律,以传染病SEIR流行模型为基础,增设病例管理人群和控制措施相关参数,从而建立起SARS的传播动力学模型。以北京市2003年SARS流行为实例,说明所建模型在干预措施效果定量评价上的应用。结果所建立的模型可以随时调整干预措施相关参数。通过干预情景假定,可以模拟各种干预措施情况下SARS的流行过程,从而对干预措施效果做出定量评价。实例研究发现,该模型可以较好地模拟北京市2003年SARS流行过程;北京市2003年4月20日前后采取的措施对SARS疫情控制起到了关键性的作用。结论所建立的SARS流行模型是可靠和稳定的,可以用于SARS干预措施效果的定量评价。     

北京市SARS流行病学分析

目的　分析北京市严重急性呼吸综合征 (SARS)流行病学特征。方法　对北京市疾病预防控制中心 2 0 0 3年SARS疫情数据库进行分析。结果　北京市SARS流行过程分五个阶段 ,各阶段发病构成如下 :输入扩散期 (3月 1～ 31日 )为 2 .7% ;上升期 (4月 1～ 15日 )为 13.6 % ;高峰期 (4月16日至 5月 4日 )为 71.0 % ;下降期 (5月 5～ 18日 )为 11.6 % ;终止期 (5月 19～ 2 8日 )为 1.1%。北京市SARS临床诊断病例 2 5 2 1例 ,发病率为 18.5 7/10万 ,死亡 192例 ,死亡率和病死率分别为 1.4 1/10万和 7.6 %。男女发病比例为 1∶0 .97,2 0～ 2 9岁组发病率最高 (30 .85 /10万 ) ,0～ 14岁组最低 (2 .5 4 /10万 ) ,患者以青壮年为主 ,占 72 .3%。城区、近郊区和远郊区 (县 )发病率分别为 32 .2 5 /10万、2 0 .5 7/10万和 8.90 /10万 ,呈现随人口密度下降发病逐渐下降的趋势。不同职业中 ,医务人员 (17.3% )、干部职员 (12 .9% )、离退休人员 (11.4 % )、工人 (9.7% )和家务待业人员 (8.8% )居发病构成前五位。病死率随年龄显著升高。结论　北京市是全球SARS流行强度最高的地区 ,但是病死率最低。     

Effectiveness of control measures during the SARS epidemic in Beijing: a comparison of the Rt curve and the epidemic curve

One of the areas most affected by SARS was Beijing with 2521 reported cases. We estimate the effective reproductive number Rt for the Beijing SARS epidemic, which represents the average number of secondary cases per primary case on each day of the epidemic and is therefore a measure of the underlying transmission dynamics. Our results provide a quantitative assessment of the effectiveness of public health control measures. More generally, our results illustrate how changes in Rt will reflect changes in the epidemic curve.     

Monitoring the severe acute respiratory syndrome epidemic and assessing effectiveness of interventions in Hong Kong Special Administrative Region

OBJECTIVE: To estimate the infection curve of severe acute respiratory syndrome (SARS) using the back projection method and to assess the effectiveness of interventions. DESIGN: Statistical method. DATA: The daily reported number of SARS and interventions taken by Hong Kong Special Administrative Region (HKSAR) up to 24 June 2003 are used. METHOD: To use a back projection technique to construct the infection curve of SARS in Hong Kong. The estimated epidemic curve is studied to identify the major events and to assess the effectiveness of interventions over the course of the epidemic. RESULTS: The SARS infection curve in Hong Kong is constructed for the period 1 March 2003 to 24 June 2003. Some interventions seem to be effective while others apparently have little or no effect. The infections among the medical and health workers are high. CONCLUSIONS: Quarantine of the close contacts of confirmed and suspected SARS cases seems to be the most effective intervention against spread of SARS in the community. Thorough disinfection of the infected area against environmental hazards is helpful. Infections within hospitals can be reduced by better isolation measures and protective equipments.     

传染病流行模型中高维非线性参数估计方法

目的研究根据流行数据逆向估计流行模型中高维非线性参数的方法。方法采用Gepasi3.3软件中的全局优化方法估计非线性传播动力学模型中的各个参数。以SARS流行模型的参数估计为例说明其应用。结果流行模型中各状态变量之间互相转换的公式可以方便地移植到Gepasi软件中的模型定义部分。选择适当的全局优化算法,容易估计出与实际流行数据拟合最佳的各个参数的取值。实例研究发现,Gepasi软件中的遗传算法可以用于估计SARS流行模型中的未知参数。采用估计参数模拟的北京每日新增SARS临床诊断病例数与实际的流行数据相比无明显差异(P>0.05)。结论Gepasi软件中的全局优化方法是强健和可靠的,可以用于流行模型中高维非线性参数的估计。     

Different epidemic curves for severe acute respiratory syndrome reveal similar impacts of control measures

Severe acute respiratory syndrome (SARS) has been the first severe contagious disease to emerge in the 21st century. The available epidemic curves for SARS show marked differences between the affected regions with respect to the total number of cases and epidemic duration, even for those regions in which outbreaks started almost simultaneously and similar control measures were implemented at the same time. The authors developed a likelihood-based estimation procedure that infers the temporal pattern of effective reproduction numbers from an observed epidemic curve. Precise estimates for the effective reproduction numbers were obtained by applying this estimation procedure to available data for SARS outbreaks that occurred in Hong Kong, Vietnam, Singapore, and Canada in 2003. The effective reproduction numbers revealed that epidemics in the various affected regions were characterized by markedly similar disease transmission potentials and similar levels of effectiveness of control measures. In controlling SARS outbreaks, timely alerts have been essential: Delaying the institution of control measures by 1 week would have nearly tripled the epidemic size and would have increased the expected epidemic duration by 4 weeks.     

突发公共卫生事件流动人口健康教育需求调查

目的了解流动人口在SARS突发事件中对健康教育的需求情况。方法对北京、太原、哈尔滨的流动人口进行个人问卷调查,对相关人员进行访谈。结果流动人口在对健康教育信息的知晓时间、渠道方面可及性差:仅有13.4%在SARS危机初现时知晓,时间段整体晚于城市、农村人群(P<0.01);知晓途径主要依赖于传统的大众媒体电视、报纸,在及时程度、信息量和信任度方面对电视的评价最高,电视宣传是流动人口最乐于接受的教育方式(73.8%)。通过在SARS期间普遍开展的健康教育活动,流动人口对疾病的主要症状和传播途径知晓程度较高,回答正确率分别为89.8%和73.4%,而对SARS病原体等知晓率低。SARS期间90.2%的流动人口采取了防护措施,但SARS后,总的行为改变率降至63.3%。流动人口对SARS期间采取的健康教育措施满意度评价与年龄、对事件的关注程度相关,总体满意率69.2%。结论针对流动人口特点,细化健康教育的策略和手段,依托基层网络,加强常规期健康教育,建立促进流动人口健康行为持续改变的长效机制,是预防突发公共卫生事件重要措施。     

SARS流行期间北京三所高校学生心理状况影响因素分析

目的 了解严重急性呼吸综合征(SARS)流行期间北京高校学生心理状况并探索其影响因素。方法 采用精神症状自评量表(SCL-90)和一般情况调查表,按分层整群抽样方法,对北京市3所重点院校6800名学生进行自评问卷调查。结果 回收有效问卷6280份。SARS流行期间学校提供了良好的社会支持系统。SCL-90阳性症状检出率为7.3％。文科学生(OR=2.00)、对防治SARS措施不了解(OR=1.91)、认为控制SARS措施无效(OR=2.25)、对战胜SARS没有信心(OR=3.57)是SCL-90阳性症状检出的危险因素,女性(OR=0.77)、研究生学历(OR=0.38)、封闭式管理对学习和个人生活无影响(OR=0.54)是SCL-90阳性症状检出的保护因素。结论 SARS流行期间,大学生心理状况受到SARS的知识和态度的影响,完善的社会支持系统有利于学生保持良好的心理健康状况。     

SARS流行期间北京市临床供血的管理

目的探讨北京市在发生重大疫情时,如何保障临床安全用血和预防因输血引起的医源性医院感染. 方法对北京在SARS期间保障临床安全用血的措施和方法进行总结和比较分析. 结果北京血液中心在SARS期间采取的应急方案,满足了临床安全用血. 结论在发生重大疫情时,通过及时有效的组织、科学有序的资源调配、安全可靠的质量保证,可以保障在发生各种灾害和事故时血液的安全供应,以预防因输血引起的医源性医院感染.     

传染性非典型肺炎分布特征及报告质量分析

目的 :分析传染性非典型肺炎 (SARS)分布特征 ,评价疫情报告质量 ,为今后制定对策提供依据。方法 :收集全国内地 SARS疫情及相关资料 ,采用统计学软件进行分析。结果 :医务人员发病率是其他人群的 5 6 .5 8倍 ;流行期间从事 SARS诊治的医务人员发病概率为 0 .5 36 /10 0人天 ,采取综合措施后下降至 0 .0 4 2 /10 0人天以下 ;6个流行强度较大的省市医务人员发病构成比明显高于其它省市 ;首发病例与北京有关省市的病死率明显高于与广东有关的省市 ;除北京外全国内地其它地区疑似病例漏报严重。结论 :医务人员的发病水平对当地 SARS流行强度影响较大 ;建议修订诊断标准和使用监测系统敏感性评价指标     

Elevation and cholera: an epidemiological spatial analysis of the cholera epidemic in Harare, Zimbabwe, 2008-2009

ABSTRACT: BACKGROUND: In highly populated African urban areas where access to clean water is a challenge, water source contamination is one of the most cited risk factors in a cholera epidemic. During the rainy season, where there is either no sewage disposal or working sewer system, runoff of rains follows the slopes and gets into the lower parts of towns where shallow wells could easily become contaminated by excretes. In cholera endemic areas, spatial information about topographical elevation could help to guide preventive interventions. This study aims to analyze the association between topographic elevation and the distribution of cholera cases in Harare during the cholera epidemic in 2008 and 2009. METHODS: We developed an ecological study using secondary data. First, we described attack rates by suburb and then calculated rate ratios using whole Harare as reference. We illustrated the average elevation and cholera cases by suburbs using geographical information. Finally, we estimated a generalized linear mixed model (under the assumption of a Poisson distribution) with an Empirical Bayesian approach to model the relation between the risk of cholera and the elevation in meters in Harare. We used a random intercept to allow for spatial correlation of neighbouring suburbs. RESULTS: This study identifies a spatial pattern of the distribution of cholera cases in the Harare epidemic, characterized by a lower cholera risk in the highest elevation suburbs of Harare. The generalized linear mixed model showed that for each 100 meters of increase in the topographical elevation, the cholera risk was 30\% lower with a rate ratio of 0.70 (95\% confidence interval=0.66-0.76). Sensitivity analysis confirmed the risk reduction with an overall estimate of the rate ratio between 20\% and 40\%. DISCUSSION: This study highlights the importance of considering topographical elevation as a geographical and environmental risk factor in order to plan cholera preventive activities linked with water and sanitation in endemic areas. Furthermore, elevation information, among other risk factors, could help to spatially orientate cholera control interventions during an epidemic.