在
托福阅读真题再现：
第一个传染阶段，主要是由于医疗差，人口发展，开始农业，人与人，以及动物之间的接触越来越多，疾病开始大规模的传染。第二，医疗得以发展，传染病被克服，但是由于经济的发展，生活水平不断上升，慢性病开始占据主导地位，比如心脏病，肺结核等。第三，到了现代社会，传染病重新出现，慢性病也没有被克服，细菌产生了抗力，很多以前没有出现的疾病开始出现了。
相关背景：
Only some diseases such as influenza are contagious and commonly believedinfectious. The micro-organisms that cause these diseases are known aspathogens and include varieties of bacteria, viruses, protozoa and fungi. Infectious diseases can be transmitted, e.g. byhand-to-mouth contact with infectious material on surfaces, by bites of insects or other carriers of the disease, and from contaminatedwater or food (often via fecal contamination), etc. In addition,there are sexually transmitteddiseases. In some cases, microorganisms that are not readily spread fromperson to person play a role, while other diseases can be prevented orameliorated with appropriate nutrition or other lifestyle changes. Somediseases, such as most (but not all) forms of cancer, heart disease, and mental disorders,are non-infectious diseases. Manynon-infectious diseases have a partly or completely genetic basis (see genetic disorder) and may thus betransmitted from one generation to another. Social determinants of health are the social conditions in whichpeople live that determine their health. Illnesses are generally related tosocial, economic, political, and environmentalcircumstances. Social determinants of health have been recognized by severalhealth organizations such as the Public Health Agency of Canada and the World Health Organization togreatly influence collective and personal well-being. The World HealthOrganization's Social Determinants Council also recognizes Social determinants of health inpoverty. When the cause of a disease is poorly understood, societies tend tomythologize the disease or use it as a metaphor or symbol of whatever that cultureconsiders evil. For example, until the bacterial cause of tuberculosis was discovered in 1882, expertsvariously ascribed the disease to heredity,a sedentary lifestyle, depressedmood, and overindulgence in sex, rich food, or alcohol—all the social ills of the time.
Disease burden is the impact of a health problem inan area measured by financial cost, mortality, morbidity, or other indicators.There are several measures used to quantify the burden imposed by diseases onpeople. The years of potentiallife lost (YPLL) is a simple estimate of the number of years that a person'slife was shortened due to a disease. For example, if a person dies at the ageof 65 from a disease, and would probably have lived until age 80 without thatdisease, then that disease has caused a loss of 15 years of potential life.YPLL measurements do not account for how disabled a person is before dying, sothe measurement treats a person who dies suddenly and a person who died at thesame age after decades of illness as equivalent. In 2004, the World HealthOrganization calculated that 932million years of potential life were lost to premature death. The quality-adjusted life year (QALY) and disability-adjusted life year (DALY) metrics are similar, but takeinto account whether the person was healthy after diagnosis. In addition to thenumber of years lost due to premature death, these measurements add part of theyears lost to being sick. Unlike YPLL, these measurements show the burdenimposed on people who are very sick, but who live a normal lifespan. A diseasethat has high morbidity, but low mortality, has a high DALY and a low YPLL. In2004, the World Health Organization calculated that 1.5 billiondisability-adjusted life years were lost to disease and injury. Inthe developed world, heartdisease and stroke cause the most loss of life, but neuropsychiatric conditions like majordepressive disorder cause themost years lost to being sick.
(编辑：Sally)