The Number of Interviews Needed to Yield New Syphilis and Human Immunodeficiency Virus Cases Among Partners of People Diagnosed With Syphilis, North Carolina, 2015

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To increase investigation efficiency.

Study Design

Retrospective review of North Carolina 2015 syphilis investigations, using the number of cases needed to interview (NNTI) and the total number of cases and contacts needed to interview (TNTI) to compare yield of new syphilis and human immunodeficiency virus diagnoses between patient groups.


We reviewed 1646 early syphilis cases and 2181 contacts; these yielded 241 new syphilis cases (NNTI, 6.9; TNTI, 16.4) and 38 new human immunodeficiency virus cases (NNTI, 43). Interviews of women (prevalence difference [PD] = 6%, 95% confidence interval [CI], 12–16), patients <30 years old (PD = 5%, 95% CI, 1–8), and patients with titer >1:16 (PD = 5%, 95% CI, 1–9) yielded more new syphilis cases in our adjusted model; no other patient factors increased investigation yield.


The NNTI and TNTI are useful measures of efficiency. Prioritizing early syphilis investigation by gender, rapid plasmin reagin titer, and age provides small increases in efficiency; no other factors increased efficiency.

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