认真阅读下列短文，并根据所读内容在文章后表格中的空格里填入一个最恰当的单词。
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The most serious health problem in the world used to be infectious(传染的)diseases such as typhoid fever, flu, bubonic plague(黑死病). In the 14th century, for example, bubonic plague killed roughly one-third of the population of Asia and about half of the population of Europe. A flu epidemic（传染病） in 1918 killed millions of people around the world. Today, however, vaccines and antibiotics have prevented the spread of many serious diseases. In fact, in many parts of the world today, infectious diseases are no longer considered to be the most serious health problem. In the United States, the number one health problem is the new epidemic of obesity（肥胖）.
