Needle sharing is a major cause of blood-borne diseases making understanding needle sharing behavior imperative to devising strategies to reduce the disease burden. A DNA-based method, using highly informative genetic markers of short tandem repeats (STRs) is being proposed as a gold standard measure to identify single-use and multi-use syringes. Self-reports of needle sharing, which have been the main source of sharing information for research, will be compared to the genotypic results to validate the responses on such risk behavior. Genotypic information from four autosomal STRs will be used to differentiate DNA from a single versus multiple individuals in syringe exudates obtained from injection drug users (IDUs) from the Baltimore needle exchange program (BNEP) studied by ALIVE II. Detecting three or more distinct alleles at an autosomal STR in the syringe exudates provides evidence that the syringe has been shared by at least two individuals. Matching probabilities will be used to match the genotypic profile of the individual(s) checking in and returning the syringe to allele(s) observed in the syringe exudates, and a mixture discrimination probability will be used to measure the likelihood of single vs. multi genome in the syringe samples. Behavioral surveillance to document the rapid spread of infectious disease from needle sharing among high-risk sub-population such as IDUs are critical for global public health along with the development and implementation of timely interventions.
