Methods A total of 7482 residents aged 15-69 selected in representative 30 counties through multi-stage random sampling from Zhejiang Province were surveyed by using questionnaire.
2
方法对社区人群采用多阶段分层整群随机抽样方法抽取研究对象，进行个案调查和血清学检测。
Methods Subjects were collected from community population by stratified multi-stage cluster sampling method. The data gathered from case investigation and serological detection.
3
方法采用分层多阶段随机抽样法，获取样本。并采取问卷的形式进行调查。
Methods Multistage sampling and stratified sampling were used and information was gathered by interview with questionnaires.
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