The utility of index case recruitment for establishing couples’ eligibility: An examination of consistency in reporting the drug use of a primary partner among sexual minority male couples.

Sexual minority men are disproportionately impacted by substance use, which is associated with greater HIV transmission behaviors. Novel approaches to drug use prevention and treatment are needed. Couple-based approaches have garnered significant attention. The recruitment of couples into substance use interventions has proven challenging. We evaluate an index-case approach to screening participants in couples' research. Seventy index cases, aged 18-29, and their main partner (140 individuals), were recruited. At screening, index participants reported their drug use and their partners' drug use for the previous 30 days. At baseline, both partners reported their drug use over the past 30 days. Individuals' self-reports and perceptions of their partner's concurrency were compared within couples using the κ (Kappa) coefficient. We found high levels of personal predictive accuracy from screening to baseline for cannabis ( κ = .81, p < .01) and cocaine/crack ( κ = .70, p < .01). Predictive accuracy of index case reporting of their partner's drug use behavior were moderately high among cocaine/crack use ( κ = .68, p < .01) and MDMA/GHB/Ketamine ( κ = .56, p < .01). Perceived partner similarity for recent drug use was also high for all drugs, with the highest levels among cocaine/crack ( κ = .82) and prescription drugs ( κ = .81). This study demonstrates that index partners report drug use with differing levels of agreement between drug types. Index recruitment has advantages in determining drug use-related eligibility requirements. Discrepancies in reporting were more frequently false positives, which reduces the risk of screening out potentially eligible couples.