A new approach to measuring the synergy in a syndemic: Revisiting the SAVA syndemic among urban MSM in the United States

Abstract

ABSTRACT Syndemic theory hypothesises that observed clusters of diseases are the result of harmful social conditions. Critiques of syndemics present the theory as ambiguous and lacking empirical evidence. Syndemics are evidenced through qualitative assessments drawing on observations, epidemiology, and biomedical evidence to explain bio-bio and bio-social interactions. Quantitative syndemic studies commonly apply a summative approach, whereby the outcome is a result of the cumulative effect of the individual elements. More recently, quantitative studies apply analyses to assess mechanical interactions among conditions. This paper applies a synergy factor analysis to measure synergy – the enhancement of the effect of one element on the effect of the others. Data from the canonical quantitative syndemic analysis study was reanalysed to assess synergy among the elements of the SAVA syndemic (substance ab/use, violence, HIV/AIDS). Contrary to original study findings, which applied a summative approach, no synergy was measured. Synergistic interactions were confirmed among a subset of the study population; the effects of substance ab/use and violence on HIV were more than two times greater in White MSM than the predicted joint effect (SF = 2·32, 95%CI 1·02–5·11, p = 0·044), indicating synergy. Synergy factor analysis presents an accessible tool to measure syndemic interactions and facilitate timely global health responses.