应用电子计算机拟合麻风年龄患病专率的改进催化模型

本文通过电子计算机对江苏省八个地区麻风年龄患病专率的理论拟合,提出了适用于麻风年龄患病专率分布的改进催化模型及其变量代换公式,并对结果进行了分析探讨。作者认为,麻风年龄患病专率可以用改进的催化模型来模拟;它是一条S形曲线,开始上升缓慢,然后快速上升,达到顶点后又缓慢下降;这反映了麻风病潜伏期和病期长、发病率低的特点。两级催化模型中的三个参数a、b、k,分别代表了疾病感染力、疾病消除速度和防治效果指数;可以应用催化模型对不同时期、不同地区的疾病年龄患病率拟合分析,对疾病的感染力。人群消除疾病的能力和防治效果进行综合评价。     

应用两级催化模型对自然人群乙肝表面抗原携带率年龄分布的分析

1959年Muench,H介绍了流行病学催化模型的简单、可逆、两级三个基本型的原理、方法和应用,之后,国内外一些学者,在疾病防治实践中,越来越多地应用该模型阐明某些疾病的流行特征、人群感染和免疫的规律,评价防治效果,定量地测量传染病在人群中的传播速度等,收到了满意的效果.本文试用两级催化模型,对泰安市自然人群乙型肝炎病毒表面抗原(HBsAg)年龄别阳性资料进行拟合,以分析人群年龄分布特征、流行程度及感染力等.1 模型与材料1.2 模型 设某易感人群暴露于一恒定的感染力中,人群易感者以a频率转变为感染者x,又以b频率     

人群华支睾吸虫感染的两级催化模型拟合分析

Ｍｕｅｎｃｈ提出的流行病学催化模型以数学模型概括一些传染病的年龄分布,定量地测定某一疾病在某地的“感染力”,反映该病在人群中的传播速度,比较不同地区或者地区防治前后某疾病的流行情况,从而评价防治效果［１］。此模型用于寄生虫病的流行病学分析,国内外已有...     

用灰色模型探讨南丹县麻风流行趋势

用磷以模型对南丹县麻风发现率进行拟合及动态预测，分析防治效果，推断未来发展趋势，其模型拟合良好，接近实际水平。研究表明南丹县麻风流行趋势已得到控制，灰色模型在麻风领域有应用价值。     

甲、乙型病毒性肝炎催化模型

1959年Mueach根据化学反应原理,提出了一组流行病学催化模型(Catalytic Epidemic Model),即将人群中的易感者比作原始反应物,用“感染力”表示催化剂,假设某疾病以一恒定“感染力”作用于人群,那么随时间变化,易感者将逐步转变成感染者(生成物分子)。应用这一类似化学中催化反应的过程,推导出一定的数学方程,描述疾病流行特征,由“感染力”定量测知传染病在人群中的传播速度,对于寻找流行因素,制订防治对策乃至评价防治效果均有较大意义。本文选择了王海涛,米尔英等人对甲型肝炎中发区的北京和乙型肝炎低发区的山西省的资料,用催化模型进行拟合分析,结果如下:     

麻风菌素试验和结核菌素试验阳性率的催化模型

催化模型(Catalytic model))原用于描述化学反应过程中催化作用的数学模型;muen-ch 将催化模型用于流行病学,提出了一组流行病学催化模型。该模型能模拟某些传染病的年龄患病率以及某些指标的年龄阳性率,以数学形式概括其年龄分布特性,定量地测量这些传染病在人群中传播的平均速度,估计某疾病的。感染力”,这对于了解疾病流行特点,评价防治效果具有一定的意义。     

可逆与两级复合型催化模型在钩虫感染流行病学中的应用

本文应用可逆与两级复合型催化模型拟合分析了我地1984、1989年不同年龄钩虫感染率资料。并应用复合模型分析拟合了潼南县、中江县、遂宁县、南充县不同地区钩虫感染率资料,通过x~2配合适度检验,结果表明拟合良好(P>0.50)。根据模型中不同的a、b、c 值可比较分析不同地区、时间、人群该病传播的平均速度,探讨影响流行分布的因素,评价防治措施的效果。     

应用可逆与两级复合型催化模型对不同地区人群乙肝感染指标的分析

<正> 应用可逆与两级复合型催化模型对不同地区人群抗—HB_S,抗—HB_C和乙肝总感染率进行了拟合,拟合良好,结果满意。人群乙肝感染指标阳性率与年平均阳转率a值呈显著正相关,与年平均阴转率b值和阴转后不再感染的比率C值呈显著负相关,并由此可建立直线回归方程。人群中抗—HB_C年平均阳转率和阴转率实际值与理论值无显著差别。表明此模型可用于分析不同     

部队人群中甲、乙型肝炎感染率的催化模型分析

应用催化模型拟合部队人群中甲、乙型肝炎感染率的横断面调查资料,并用随后一年半时间的随访结果加以验证,结果尚称满意。所计算的人群平均感染力(r值)可以基本反映相对固定人群中甲、乙型肝炎的感染动态,可以用于甲、乙型肝炎感染在人群中动态的预测。本文通过对某航校2053人1983年12月普查结果进行分析,用简单催化模型拟合HAV感染率,计算结果:ŷ=0.9849(1-e^-0.1117t),r (感染力)=0.1117,与横断面调查结果符合良好,R²=0.9758;与随访一年半HAV新感染密度111.8/1000人年十分相近。用可逆催化模型拟合HBV感染率,计算结果为:ŷ=0.6736(1-e^-0.06t),r (感染力)=(a+b)=0.06,其中a (阳转率)=0.041,b (阴转率)=0.019,拟合结果与实际调查结果十分相近,R²=0.9487。经过一年半随访,看到HBV感染标记在相对固定人群中确呈双向改变,其阳转率大于阴转率(77.08/1000人年对10.11/1000人年),与计算的a>b总趋势相符。人群HBV感染是受多因素影响的复杂过程,所用于拟合的公式需进一步改进。     

两级催化曲线模型在肺吸虫病流行病学上的应用

本文应用两级催化模型对浙江省永嘉县的小长坑、黄过坑两村人群肺吸虫感染进行拟合,得曲线方程:ŷ（小）=1.0480（e^-0.01375t-e^-0.3t）;ŷ（黄）=1.0661（e^-0.0155t-e^-0.25t）。模型较成功地模拟了两村人群感染肺吸虫的年龄分布情况,定量测知该两村人群肺吸虫平均感染力分别为0.30、0.25。同时,通过模型分析了两村肺吸虫感染状况、人群感染的年龄分布特征等。认为感染力“a”值是一个定量估计流行区肺吸虫感染程度的指标,可作为比较各地流行状况,评价防治效果等。     

探讨低流行区麻风病疫情监测的策略

放松低流行区疫情监测工作,麻风病极有可能卷土重来。文章探讨了在麻风病低流行区,特别是麻风病处于基本消灭后的地区应采取尽可能利用现有卫生资源、注重成本一效益、主要以被动方式早期发现病人的基本策略。阐述了疫情监测工作要充分利用防病体制改革带来的资源优势;基础工作应从专业机构转移到综合性医院;注重培训方法,提高综合性医院医生参与防病的意识与责任感;主动检查家庭内接触者;采取被动监测复发的策略并强调消除疫情监测中基本消灭不等于完全控制、LEC不能取代疫情监测以及基层防保人员不再是疫情监测的主力军的认识上的几个误区。     

Leprosy: too complex a disease for a simple elimination paradigm

Can leprosy be eliminated? This paper considers the question against the background of the WHO programme to eliminate leprosy. In 1991 the World Health Assembly set a target of eliminating leprosy as a public health problem by 2000. Elimination was defined as reaching a prevalence of < 1 case per 10 000 people. The elimination programme has been successful in delivering highly effective antibiotic therapy worldwide. However, despite this advance, new-case detection rates remain stable in countries with the highest rates of endemic leprosy, such as Brazil and India. This suggests that infection has not been adequately controlled by antibiotics alone. Leprosy is perhaps more appropriately classed as a chronic stable disease than as an acute infectious disease responsive to elimination strategies. In many countries activities to control and treat leprosy are being integrated into the general health-care system. This reduces the stigma associated with leprosy. However, leprosy causes long-term immunological complications, disability and deformity. The health-care activities of treating and preventing disabilities need to be provided in an integrated setting. Detecting new cases and monitoring disability caused by leprosy will be a challenge. One solution is to implement long-term surveillance in selected countries with the highest rates of endemic disease so that an accurate estimate of the burden of leprosy can be determined. It is also critical that broad-based research into this challenging disease continues until the problems are truly solved.     

A Bayesian approach to study the space time variation of leprosy in an endemic area of Tamil Nadu, South India

Background

In leprosy endemic areas, patients are usually spatially clustered and not randomly distributed. Classical statistical techniques fail to address the problem of spatial clustering in the regression model. Bayesian method is one which allows itself to incorporate spatial dependence in the model. However little is explored in the field of leprosy. The Bayesian approach may improve our understanding about the variation of the disease prevalence of leprosy over space and time.

Methods

Data from an endemic area of leprosy, covering 148 panchayats from two taluks in South India for four time points between January 1991 and March 2003 was used. Four Bayesian models, namely, space-cohort and space-period models with and without interactions were compared using the Deviance Information Criterion. Cohort effect, period effect over four time points and spatial effect (smoothed) were obtained using WinBUGS. The spatial or panchayat effect thus estimated was compared with the raw standardized morbidity (leprosy prevalence) rate (SMR) using a choropleth map. The possible factors that might have influenced the variations of prevalence of leprosy were explored.

Results

Bayesian models with the interaction term were found to be the best fitted model. Leprosy prevalence was higher than average in the older cohorts. The last two cohorts 1987–1996 and 1992–2001 showed a notable decline in leprosy prevalence. Period effect over 4 time points varied from a high of 3.2% to a low of 1.8%. Spatial effect varied between 0.59 and 2. Twenty-six panchayats showed significantly higher prevalence of leprosy than the average when Bayesian method was used and it was 40 panchayats with the raw SMR.

Conclusion

Reduction of prevalence of leprosy was 92% for persons born after 1996, which could be attributed to various intervention and treatment programmes like vaccine trial and MDT. The estimated period effects showed a gradual decline in the risk of leprosy which could be due to better nutrition, hygiene and increased awareness about the disease. Comparison of the maps of the relative risk using the Bayesian smoothing and the raw SMR showed the variation of the geographical distribution of the leprosy prevalence in the study area. Panchayat or spatial effects using Bayesian showed clustersing of leprosy cases towards the northeastern end of the study area which was overcrowded and population belonging to poor economic status.     

Effects of dependent errors in the assessment of diagnostic test performance

Latent class models can be used to assess diagnostic test performance when there is no perfectly accurate gold standard test available for comparison. These models usually assume independent errors between the tests, conditional on the true disease state of the subject. Maximum likelihood estimates of the prevalence of the disease and the error rates of diagnostic tests are then obtained. This paper examines the impact of error dependencies between binary diagnostic tests on the parameter estimates obtained from the latent class models. The independence model often gives parameter estimates having relatively small bias, but in some situations (for example, when disease prevalence is low and the tests have low specificity, such as in population screening) the bias may be more serious. © 1997 John Wiley & Sons, Ltd.     

A seroepidemiologic study of hepatitis A virus infections: statistical analysis of two independent cross-sectional surveys in Okinawa, Japan

To investigate the endemic situation of hepatitis A virus infection in the past in Okinawa, Japan, the authors analyzed two sets of cross-sectional data on age-specific prevalence of antibody to hepatitis A virus (anti-HAV) obtained in 1968-1973 and 1980-1981 by fitting a catalytic model. For these two sets of data, the asymptotic level of infectious force of hepatitis A virus, namely lambda infinity, was estimated as 0.121 and 0.149, the maximum slope of the time-dependent force of hepatitis A infection, namely alpha, was 0.566 and 0.529, and the year when the force of hepatitis A infection had decreased to the half of lambda infinity, namely beta, was 1966 and 1964, respectively. In the test for the equality of parameters for the two applications, the difference was not significant. Furthermore, the fitness of the catalytic model to the data on anti-HAV prevalence was good. The results of the analysis by fitting the catalytic model show that hepatitis A infection had been highly endemic, that is, 136 infections per 1,000 persons per year in the area studied before 1955, and it decreased rapidly during the 1960s. Since 1975, hepatitis A has been a rare disease (infection is almost zero per 1,000 persons per year) in Okinawa, Japan.     

Methods for projecting the incidence and prevalence of chronic diseases in aging populations: application to Alzheimer's disease

Projections of the incidence and prevalence of disease are important for public health planning. This paper describes methods for projecting the incidence and prevalence of a chronic disease in ageing populations. The approach uses age-specific disease incidence rates together with assumptions about survival to reconstruct disease prevalence. The methods can be used to evaluate the potential impact of public health interventions that may prevent disease or prolong survival. We used the methods to project the future prevalence of Alzheimer's disease in the United States. We found that the prevalence of Alzheimer's disease will nearly quadruple over the next 50 years. Although projections of the absolute prevalence are sensitive to assumptions about the age-specific incidence rates of disease, the proportionate growth is relatively insensitive. The increase in prevalence results from the ageing of the U.S. population. In order to perform the calculations, we have assembled U.S. Census population projections and U.S. mortality rates into computer software that is available from the authors at www.jhsph.edu/Departments/Biostats/software.h tml.     

Prospects for the elimination of leprosy as a public health problem in the State of Paraná, Brazil

Leprosy, an endemic contagious/infectious disease, is still a public health problem in most States of Brazil, despite an important decrease in the prevalence rate in recent years. The current study aims to analyze the prospects for the elimination of leprosy in the State of Paraná, based on detection and prevalence rates for the years 2000 to 2005, in addition to data on gender, age, clinical form, operational classification, and number of skin lesions. Data were obtained from the Reportable Diseases Information System (SINAN) and the Tabnet software. Leprosy detection and prevalence rates in Paraná remained unaltered during the study period. The leprosy detection rates were high or very high in the majority of the health districts in the State. In terms of prevalence, eight health districts had reached the goal of eliminating the disease. In conclusion, the State of Paraná is close to reaching the goal of eliminating leprosy. Based on the study results, actions are recommended to eliminate the disease as a public health problem.     

The use of simple epidemiological models in the evaluation of disease control programmes: a case study of trachoma

One of the problems in the quantitative evaluation of disease control programmes is the definition of a “critical” index reflecting the effect of control measures on the various aspects of a polymorphic disease. Trachoma is an example of a polymorphic disease in which its activity, intensity, severity, etc., are affected by control measures, including their timing. A simple epidemiological model indicated that the “force of infection” is a sufficient parameter to describe changes in the disease picture following a control programme. Use was made of two trachoma prevalence sample surveys in the same communities, one carried out in 1960-61 and the other in 1968-69. Total trachoma age-prevalence histograms were constructed and simple catalytic curves fitted with the help of a computer programme developed for this purpose. A reduction in the force of infection in the cohort born after the institution of control measures was found. Its projection to the whole community indicated that the control programme had reduced the disease load to 20.1%, i.e., about two-fifths of its former level.     

Human Papillomavirus Vaccination at a Time of Changing Sexual Behavior

Human papillomavirus (HPV) prevalence varies widely worldwide. We used a transmission model to show links between age-specific sexual patterns and HPV vaccination effectiveness. We considered rural India and the United States as examples of 2 heterosexual populations with traditional age-specific sexual behavior and gender-similar age-specific sexual behavior, respectively. We simulated these populations by using age-specific rates of sexual activity and age differences between sexual partners and found that transitions from traditional to gender-similar sexual behavior in women <35 years of age can result in increased (2.6-fold in our study) HPV16 prevalence. Our model shows that reductions in HPV16 prevalence are larger if vaccination occurs in populations before transitions in sexual behavior and that increased risk for HPV infection attributable to transition is preventable by early vaccination. Our study highlights the importance of using time-limited opportunities to introduce HPV vaccination in traditional populations before changes in age-specific sexual patterns occur.