方法采用分组对照研究的方法，检查组与对照组对结核菌素纯蛋白衍化物（PPD）试验的反应情况。
METHODS In a cross-sectional survey, we studied purified protein derivative(PPD) test in exposure group and control group.
方法采用分组对照研究的方法，检查组与对照组对结核菌素纯蛋白衍化物（PPD）试验的反应情况。
METHODS In a cross-sectional survey, we studied purified protein derivative(PPD) test in exposure group and control group.
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