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

Samoff, Erika MPH, PhD*; Cope, Anna B. MPH, PhD; Maxwell, Jason BS*; Thomas, Francina BS*; Mobley, Victoria L. MD, MPH*

doi: 10.1097/OLQ.0000000000000637
Original Studies

Compare syphilis investigation yield among patient groups using number needed to interview.

Goal 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.

Results 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.

Conclusions 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.

We assessed syphilis investigation efficiency using number of patients and contacts needed to find new cases. Patient information, including information on newer partner-finding practices, did not increase syphilis investigation efficiency.

From the *North Carolina Division of Public Health Communicable Disease Branch, Raleigh, NC; and †Centers for Disease Control and Prevention, Division of Sexually Transmitted Disease Prevention, Atlanta, GA

Acknowledgements: The authors gratefully acknowledge the effort and contribution of the disease investigation staff whose work is analyzed here. The authors are also grateful to Aaron Fleischauer, Roger Follas, and Mike Cassell for thoughtful comments on the analysis.

Financial support: This project was supported by the US Centers for Disease Control and Prevention and the State of North Carolina but did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily reflect the official position of the Centers for Disease Control and Prevention, or the authors' affiliated institutions.

Correspondence: Erika Samoff, MPH, PhD, North Carolina Division of Public Health Communicable Disease Branch 1902 Mail Service Center Raleigh, NC 27699-1902. E-mail:

Received for publication January 27, 2017, and accepted April 4, 2017.

© Copyright 2017 American Sexually Transmitted Diseases Association