Background: Harm reduction services such as safer injection supply distribution are essential to reducing morbidity and mortality among people who use drugs (PWUD); however, local use of harm reduction supplies (e.g., tourniquets, saline solution) is difficult to routinely and systematically monitor. The purpose of this study was to develop and validate a systematic social observation tool designed to assess use of harm reduction supplies at the street block level.Methods: Data collection took place on a random sample of 150 blocks located throughout the Kensington neighborhood of North Philadelphia from November 2021 to January 2022. We measured inter-rater reliability by two-way mixed-effects intra-class correlation coefficients (ICC) with the consistency agreement definition and internal consistency reliability using Cronbach's alpha and McDonald's omega. Exploratory factor analysis with principal component extraction and promax rotation assessed internal consistency. We validated scales against locations of public syringe disposal boxes, a proxy measure for areas of concentrated drug use, using logistic regression.Results: Naloxone canisters, syringe caps, saline and sterile water solution bottles showed the highest reliability (ICC >= 0.7). Items also showed high internal consistency (alpha, omega>0.7). Exploratory factor analysis identified one, three-item scale with high internal consistency: syringe caps, vials, and baggies (alpha = 0.85; omega = 0.85)-all supplies used concurrently with drug injection but not discarded in syringe disposal boxes. Drug use (OR = 1.78, 95 % CI = (1.48, 2.23)), harm reduction (OR = 3.53, 95 % CI = (2.20, 6.12)), and EFA scales (OR = 1.85, 95 %CI = (1.51, 2.34)) were significantly and positively associated with being within walking distance (<= 0.25 miles or 0.4 km) of a syringe disposal box.Conclusion: This study provides an efficient tool with high reliability and validity metrics to assess community uptake of harm reduction supplies designed for use by community organizations, policy makers, or other groups providing resources to PWUD.
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