Short tandem repeat methodology for genotypic identi®cation of single-person versus multi-person use of syringes Sadeep Shrestha a,b , Steffanie A. Strathdee b , Heena Brahmbhatt b , Homayoon Farzadegan b , David Vlahov b,c and Michael W. Smith a Objective: To develop laboratory methods to differentiate between single- versus multi-person use of syringes by injection drug users. Methods: Forensic short tandem repeat (STR) genetic analysis was undertaken to cross-validate a test panel of trace blood contents from syringes representing single- versus multi-person syringe use. Laboratory-simulated scenarios of needle sharing generated 34 syringe washes that were blinded for evaluation. Polymerase chain reaction was used to amplify the polymorphic STR locus D6S502 from blood trace contents in used syringes. Alleles were sized and quanti®ed using a commercial gene sequencer. A statistical algorithm was developed to determine the number of alleles present in the ampli®ed DNA fragments. Syringes with more than two expected alleles were considered to represent multi-person syringe use. Sensitivity, speci®city and the kappa coef®cient were calculated. Results: Allelic matrix-based analysis of alleles from the single STR successfully characterized single-use (n  12) and multiple-use (n  22) syringes with 68% sensi- tivity and 100% speci®city upon re-analysis. The extent of agreement over and above chance (kappa  0.6; P , 0.0001) indicated good agreement for differentiating single- versus multi-person syringe use. Conclusions: These ®ndings suggest that improved genotypic STR analysis of syringe material could be an adjunct to methods for validating self-reported needle sharing, conducting behavioral surveillance of needle-sharing behaviors, and evaluating inter- ventions such as needle-exchange programs. Assays based on multiple STR loci will undoubtedly improve upon the promising results obtained from laboratory simulations of needle sharing. & 2000 Lippincott Williams & Wilkins AIDS 2000, 14:1507±1513 Keywords:Syringe sharing, risk behaviour validity, forensics, self-reporting, short tandem repeat (STR) From the a Intramural Research Support Program, Science Applications International Corp. Frederick, National Cancer Institute, Frederick Cancer Research and Development Center, Frederick, the b Johns Hopkins School of Hygiene and Public Health, Baltimore, Maryland and the c Center for Urban Epidemiologic Studies, New York Academy of Medicine, New York, New York, USA. Sponsorship: This project was funded in part with federal funds from the National Cancer Institute, National Institutes of Health, under Contract No. NO1-CO-56000, and through a grant from the National Institute on Drug Abuse (DA09225). Note: The content of this publication does not necessarily re¯ect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the US Government. Correspondence to Dr. Michael W. Smith, Science Applications International Corp. Frederick, National Cancer Institute, Frederick Cancer Research and Development Center, PO Box B, Frederick, MD 21702, USA. Tel: 1 301 846 1913; fax: 1 301 846 1909; email: Michael_W_Smith@nih.gov Received: 16 November 1999; revised: 21 March 2000; accepted: 31 March 2000. ISSN 0269-9370 & 2000 Lippincott Williams & Wilkins 1507