To determine the antibody titer for the diagnosis of tsutsugamushi disease by indirect immunofluorescent test in Korea, the antibody titers of 6572 sera of the residents and 296 sera of the 109 patients confirmed as tsutsugamushi disease in the Chungcheung area were analyzed.
At cut-off point of 1：40, specificity was 98％ and sensitivity, positive predictive value and negative predictive value were 49％, 90％, 86％ during the first week after onset, 85％, 94％, 95％ during the second week, and 96％, 95％, 99％ during the third week.
At cut-off point of 1：80, specificity was 99％ and sensitivity, positive predictive value and negative predictive value were 47％, 94％, 86％ during the first week, 85％. 97％ 95％ during the second week, and 96％ 97％ 99％ during the third week.
At cut-off point of 1：160, specificity was 100％ and sensitivity, positive predictive value and negative predictive value were 31％, 99％, 82％ during the first week, 69％, 100％, 91％ during the second week, and 89％, 100％, 97％ during the third week.
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