Swine influenza (swine flu) is an acute viral infection of the respiratory tract in pigs caused by type A influenza virus.
猪流感是一种发生在猪身上的高度传染性急性呼吸道疾病，由A型流感病毒引起。
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Theory Background: Acute viral upper respiratoryinfection is a most common clinic infective disease, and about 70%-80% of it is caused by virus.
理论背景急性上呼吸道感染是临床最常见的一种感染性疾病，约有70% - 80%由病毒引起。
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Objective to study the common virusinfection of elderly hospitalized patients admitted because of acuterespiratory tract infections during winter and spring in Lanzhou district.