流行病教学课件 case-control.pptxVIP

CASE-CONTROL STUDIES Cross-sectional study 这是神马研究？ Critical design issue: Directionality Directionality defines when exposure variable is observed relative in time to when the health outcome is observed Time Exposure Disease Backward directional study Compares previous exposures in persons with and without the disease Case-control studies Common types of controls Population controls – selected from the same community as the cases Hospital-based controls – selected from the same health care institutions as the cases Example of a case-control study: legionnaires’ disease（军团病） outbreak in Bogalusa, LA Report: From October 10 through November 13 1989,33 patients were hospitalized with legionnaires disease (LD) in Bogalusa, Louisiana Research Question: What exposure factors in the previous 10 days were more commonly found among LD cases compared to LD-free controls? Twenty-eight LD case-patients confirmed by laboratory testing were included in the study Two controls per case were selected randomly from office records of the physicians who hospitalized the case-patients Case-patients and controls were interviewed by telephone using a standardized questionnaire. Participants were asked if during previous 10 days they visited or shopped at locations that were near previously identified sources of aerosolized water Results Case-patients were more likely than controls to have shopped at grocery store A (93% vs. 52%) in the 10 days before illness Employees of grocery store A were more likely than employees of other grocery stores to have high antibody titers（抗体滴度） to Legionella pneumophila serogroup 1 (Lp-1) Lp-1 was isolated from water in the reservoir of the mist machine. “Aerosols from a grocery store mist machine were the source of this outbreak.” 特 点 疾病发生后进行 分成病例组与对照组 暴露是由研究对象从现在对过去的回顾 由果推因 分析暴露与疾病的联系 病例的选择 1.要求 诊断可靠，尽量使用金标准 选择确诊的新病例 2.来源 总体人群中的全部病例或者随机样本人群中的全部病例 医院住院或门诊的病例 对照的选择 1.要求 病例和对照要求来自同一人群 对照一旦发生所研究的疾病便成为病例 组的研究对象 2.来