EPIDEMIC, an outbreak of a disease that affects a large number of individuals. Some diseases normally attack a certain proportion of the inhabitants of any area. This proportion is called the epidemic threshold of the disease. When the number of cases rises significantly above the epidemic threshold, an epidemic is said to exist. When whole continents or the entire world is involved, the outbreak is called a pandemic. During the 20^th century there have been pandemics of influenza and cholera.

流行病，一种爆发的，影响大量个体的疾病。通常，某些疾病会攻击任何地区一定比例的居民。这种比例被称为疾病的流行阈值。当病例明显高于流行病阈值时，就是说存在流行病。当涉及整个大陆或全世界时，这种爆发就被称为流行病。在20世纪曾经就发生过流行性感冒和霍乱的大流行。

In the past, epidemiologists were concerned only with transmissible diseases, such as cholera, malaria, smallpox, and yellow fever. However, it has been shown that some other types of disease tend to prevail above the normal epidemic threshold in certain areas or among certain age or socioeconomic groups. These disorders include atheroscherosis, diabetes mellitus, certain malignant tumors, and some psychiatric disorders. This article, however, is devoted to epidemics caused by infectious agents, such as bacteria rickettsias, and viruses.

过去，流行病专家只关注可传染的疾病，诸如霍乱、疟疾、天花和黄热病。然而，情况表明，一些其它类型的疾病常常在某些地区或某个年龄或社会经济组织中超过正常的流行阈值在流行。这些疾病包括动脉粥样硬化、糖尿病、某些恶性肿瘤和一些精神疾病。然而，该文专门讨论的是由传染性病原体引发的流行病，比如，立克次体细菌，以及病毒。

COURSE OF AN EPIDEMIC

   The index case, or primary case, is the first person known to have contracted the disease and transmitted it to others. After the incubation period, which varies according to the particular disease, secondary cases appear. Individual who transmit the infective organisms to others without actually having any signs or symptoms of the disease are called carriers. They as well as persons who have mild cases of the disease are not easily detected and may continue to transmit the disease to others without being recognized as sources of infection.

流行病的过程

    索引病倒，或原发病例，是已知感染了该疾病，并将它传染给其他人的第一个人。根据特定的疾病变化，在潜伏期之后出现继发性病例。将感染的微生物传染给其他人而事实上没有任何该疾病的征兆或症状的个人被称为携带者。他们以及那些有轻微状况的人不易被发现，而且可能不断将疾病传播给他人而不被认为是传染源。

In studying the course of an epidemic, scientists draw an epidemic curve by plotting on a graph the number of reported cases, deaths, or both. They also draw an epidemic map of the affected region, showing the distribution of affected individuals according to their geographic locations. These aids are useful in tracing the source, path, and course of the infection.

    在研究流行病的过程中，科学家通过在一个记录了病例、死亡或包括了这两项数字的图表上画出流行病曲线。他们也会画一个感染地区的流行病地图，根据它们的地理位置显示受到感染个体的分布情况。这些辅助手段在帮助追溯来源、路径以及感染过程时是很有用的。

   Transmission of Infective Agents.  Disease-causing organisms may be transmitted in various ways, and some may be transmitted by more than one method. Direct contact with the skin lesions of an infected person is the most frequent method of transmitting such diseases as leprosy and yaws. Some infectious agents are airborne and may be inhaled. Diseases that are spread this way include chicken pox, cerebrospinal meningitis, measles, and whooping cough. Dried excrement on clothing or bedding may also be a source of infection.

传染性病原体的传播。致病微生物会以各种不同的方式传播，而一些生物体可以通过一种以上的方法传播。直接接触感染者损伤的皮肤是传染这类疾病最常见的方式，如麻风病和热带莓疹。一些感染的病原体是由空气传播，并且可以被吸入。用这种方式传播的疾病包括水痘、脑脊膜炎、麻疹和百日咳。衣服或床上用品上的干排泄物也可以成为感染源。

   Some infections are spread by contaminated food or water. Cholera, for example, can spread rapidly in areas where water supplies are contaminated with sewage. Object on which disease-causing organisms can survive are called fomites. Examples of fomites are eating utensils, toys, laundry, and toilet seats.

    一些传染病是由污染的食物或水传播的。例如，霍乱可在供水被污水污染的地区迅速扩散。致病微生物可生存的物体被称为污染物。污染物的例子有餐具、玩具、待洗的衣物以及马桶座圈等。

   Control Measures.  Epidemic control measures include the reporting of all cases, suspected cases, and carriers; public health programs concerning personal, household, and community hygiene; the installation of adequate facilities for sewage and refuse disposal; the provision of wholesome food and water; the isolation of infected individuals; and measures to eradicate insects and other animals that may transmit the disease. The vaccination of susceptible persons may also be valuable aid in combating an epidemic. A cordon sanitaire, an enforced isolation of the affected region is seldom effective as a control measure because migrants, travelers, and others often find a way to break through it.

    控制措施。流行病控制措施包括报告所有病例、疑似病例以及携带者；有关个人、家庭和社区卫生的公共卫生计划；安装适当的污水和垃圾处理设施；以及消灭昆虫和其它可能传播疾病的动物；在与流行病的斗争中，易感染人员接种疫苗也可能是有价值的帮助。对感染地区强制隔离的封锁线作为一种控制措施很少起到作用，因为，流动人员、旅行者以及其他的人员常常会找到突破它的办法。

   The value of a particular control measure must often be weighed against its cost. Vaccination, for example, is effective against a number of diseases. However, in some diseases, such as cholera, it is very costly because vaccinations must be repeated periodically to ensure effective immunological protection. Therefore, water chlorination and the installation of sanitary sewage facilities may be cheaper and more beneficial in the long run than large-scale vaccination programs. These measures would also help protect the population against outbreaks of other intestinal infections.

特定控制措施的价值通常必须与其成本相权衡。例如，疫苗对抗许多疾病是有效的。然而，在某些病症中，例如霍乱，代价极大，因为必须定期重复注射疫苗以保证有效的免疫防护。因此，加氯的水处理与安装生活污水处理设施会成本更低，而且从长远来看，比大规模的疫苗接种计划更有利。这些措施也会帮助保护人群防止其它肠道传染病的爆发。

FACTORS AFFECIING EPIDEMICS

   The course and severity of an epidemic are affected by a variety of factors, including the virulence of the particular disease-causing organism and the makeup of the affected population.

影响流行病的因素

    流行病的过程和严重程度受到各种因素的影响，包括特殊致病微生物的毒性和感染人群的构成。

   Causative Organism.  The virulence of the organism is important in determining the severity of an epidemic. Sometimes the virulence of the organism diminishes over the years. Syphilis, for example, was a serious disease when it swept over Europe in the 16^th century but later lost some of its virulence. On the other hand, hospital staphylococcal infections are becoming increasingly severe.

    致病微生物。微生物的毒性在确定流行病的严重程度时非常重要。有时，微生物的毒性随时间推移会逐渐减弱。例如，梅毒在16世纪时是一种横扫欧洲的严重疾病，但之后它便失去了一些毒性。另一方面，医院中葡萄球菌的感染正变得越来越严重。

   Immunity of the Population.  The immunological status of the population also helps determine the severity of the epidemic. If the disease invades a virgin population—that is, one that has not been in contact with the disease previously and has no immunity to it—the ensuing epidemic may be disastrous. During World War I, for example, tuberculosis was introduced into the Balkans, and in 1915 about 150,000 persons succumbed to the disease.

    人群的免疫。人群的免疫状态也会有助于确定流行病的严重程度。如果疾病侵入原生态人群---换言之，以前没有接触该疾病，而且对它没有免疫力的人们---因而发生的流行病可能会是灾难性的。例如，在一次大战期间，结核病传入了巴尔干半岛，在1915年有大约15万人死于这种疾病。

   The likelihood of immunity to a particular disease also varies with age. Measles, for example, is rare during the first months of life because the baby receive protective antibodies from its mother.

    对于一种特殊疾病的免疫可能性也会因年龄而异。例如，麻疹在生命的最初几个月时是很少见的，因为，婴儿从其母亲那里获得了保护性抗体。

   Sex.  The difference in disease rates between men and women is sometimes due to the diversity of their work habits. For example, women washing clothes in contaminated water easily acquire waterborne diseases. Similarly, in many parts of the world the man is often a laborer, soldier, or hunter, and because he spends much time out-of-doors is likely to be exposed to infected insects and other animals.

    性别。在男人与女人之间发病率的差别有时是由于他们工作习惯的不同。例如，在受到污染的水中洗衣服的妇女更容易得水源性疾病。同样，在世界许多的地方，男人通常是劳动者，士兵或猎人，而由于他们在户外的时间很长，有可能面对感染的昆虫和其它动物。

   Sanitary conditions.  Where sanitary conditions are poor, especially in overcrowded cities, epidemics can occur easily. Outbreaks of yellow fever, for example, are common in rapidly growing tropical cities, where the poor disposal of refuse allows the breeding of aedes aegypti mosquitoes in discarded tin cans and other containers in which water can accumulate. Unsanitary food handling and contamination of water supplies with sewage are also common predisposing factors to contracting yellow fever.

卫生条件。那些卫生条件差的地方，尤其是在拥挤的城市中，很容易发生流行病。例如，在快速发展的热带城市中黄热病的爆发就是很常见的，对垃圾的处理不当使得埃及伊蚊在丢弃的锡罐和其它可能积水的容器中繁殖。不卫生食物的处理和被污水污染的供水系统也是感染黄热病常见的易发因素。

Population Movements.  The movement of itinerant laborers, tourist, and others, as well as the large-scale migration of people following disasters such as earthquakes, floods, and wars are common factors in the spread of epidemics. During the centuries of widespread sea exploration sailors carried to many parts of the world such diseases as smallpox, measles, tuberculosis, and venereal infections. As modern man seeks new ground for urban, industrial, and agricultural development he is brought into contact with insects and other animals that may be carrying diseases transmissible to man. Outbreaks of tularemia, for example, have been a frequent scourge of newly opened agricultural lands in central Asia.

人口流动。巡回的劳动者、旅游者和其他的人，以及诸如地震、洪水和战争这样的灾难随之而来的大规模人员迁徙都是流行病传播的常见因素。在几年世纪广泛的航海探险中，水手将比如天花、麻疹、结核以及性病带到了世界许多地方。随着现代人为都市、工业以及农业发展寻求新领域时，他就会接触到可能传染给人的，带有可传染疾病的昆虫和其它动物。例如，爆发的兔热病一直是中亚新开垦农业用地的灾祸。

   Other Factors.  A susceptibility or a resistance to a particular disease by a national or ethnic group may be a result of inbreeding. Jews, for example, tend to be more resistant to tuberculosis than other groups. The type of community is also important. A closed community, such as an isolated village, a jail, an army camp, or a ship, is less likely to be subject to epidemics than an open community, one to and from which people frequently migrate.

    其它因素。一个国家或种族群体对特定疾病的易感性或抵抗力可能是近亲繁殖的结果。例如，犹太人常常比其它群体对结核心病有更强的抵抗力。社区的类型也很重要。一个封闭的社区，如一个隔离的村庄，监狱，军营，或一艘船，相比一个开放的，人员经常往来的社区不太可能成为流行病的对象。

HISTORY

   There are many theories but few available facts about the large epidemics that occurred centuries ago. Major epidemics were caused by bubonic plague, cholera, malaria, smallpox, typhus, and yellow fever, but many diseases were confused with each other—for example, syphilis was sometimes confused with measles or smallpox—and their causes were unknown.

历史

    对于几个世纪以前发生的重大流行病，有许多理论，但很少有符合事实的理论。主要的流行病是由黑死病、霍乱、疟疾、天花、斑疹伤寒和黄热病引发的，但许多疾病是相互混淆的---例如，梅毒有时就与麻疹或天花混淆---而它们的原因尚不清楚。

   A major breakthrough in epidemiology occurred in 1849 during a cholera outbreak in London. The English physician John snow observed that only those who drank water from the Broad Street pump became ill. Taking the handle off the pump so that it could not be used hastened the end of the epidemic. At about the same time, the English lawyer Sir Edwin Chadwick also fought for better sanitary conditions in Britain.

流行病的重大突破出现在1849年霍乱在伦敦的爆发期间。英国医生约翰·斯诺观察到，只有从布罗德街泵站饮水的那些人才会患病。将泵站的取水手柄卸掉，使它无法使用加速了流行病的结束。与此同时，英国律师爱德温·查德威克爵士也在为改善不列颠的卫生条件在努力。

Although bacteria had been discovered in the late 1600’s, the first scientific evidence that they can cause disease was provided in 1976 by the German physician Robert Koch, who showed that the bacterium Bacillus anthracis causes anthrax. In the years that followed, thousands of other disease-causing organisms were identified and their modes of transmission studied.

尽管细菌在17世纪末才被发现，但它们会引发疾病的第一个科学证据是由德国医生罗伯特·科赫提供的，它证明炭疽杆菌会引发炭疽热。在接下来的几年中，确定了数以千计的致病微生物，并研究了它们的传播方式。

   Today, epidemiology is a complex field. Statistical methods that allow scientist to make more refined calculations and predictions are widely used in studying epidemics. A recent concept in epidemiology is the landscape epidemiology originated by the Russian scientist Evgenii Pavlovskyi in 1939, which correlates the outbreak of disease with local ecological conditions.

今天，流行病学是一个复杂的领域。允许科学家做更多精确计算和预测的统计方法已广泛地运用于流行病的研究中。流行病学中的一个新概念是由俄罗斯科学家叶夫根尼·帕夫洛夫斯基于1939年开创的环境流行病学，它将疾病的爆发与当地的生态环境联系在一起。

                                               SOCAR FELSENFELD, M. D.

                                                  Tulane University

                                       School of Public Health and Tropical Medicine

                                            索卡·费尔森菲尔德医学博士

                                                     杜兰大学

                                               公共卫生与热带医学学院

                                                  2022年8月23日译

（译者注：该词条位列《大美百科全书》1985年版，第10卷，第506页至507页）