Syndemics of psychosocial problems and HIV risk: A systematic review of empirical tests of the disease interaction concept

Abstract

In the theory of syndemics, diseases co-occur in particular temporal or geographical contexts due to harmful social conditions (disease concentration) and interact at the level of populations and individuals, with mutually enhancing deleterious consequences for health (disease interaction). This theory has widespread adherents in the field, but the extent to which there is empirical support for the concept of disease interaction remains unclear. In January 2015 we systematically searched 7 bibliographic databases and tracked citations to highly cited publications associated with the theory of syndemics. Of the 783 records, we ultimately included 34 published journal articles, 5 dissertations, and 1 conference abstract. Most studies were based on a cross-sectional design (32 [80%]), were conducted in the U.S. (32 [80%]), and focused on men who have sex with men (21 [53%]). The most frequently studied psychosocial problems were related to mental health (33 [83%]), substance abuse (36 [90%]), and violence (27 [68%]); while the most frequently studied outcome variables were HIV transmission risk behaviors (29 [73%]) or HIV infection (9 [23%]). To test the disease interaction concept, 11 (28%) studies used some variation of a product term, with less than half of these (5/11 [45%]) providing sufficient information to interpret interaction both on an additive and on a multiplicative scale. The most frequently used specification (31 [78%]) to test the disease interaction concept was the sum score corresponding to the total count of psychosocial problems. Although the count variable approach does not test hypotheses about interactions between psychosocial problems, these studies were much more likely than others (14/31 [45%] vs. 0/9 [0%]; χ2=6.25, P=0.01) to incorporate language about “synergy” or “interaction” that was inconsistent with the statistical models used. Therefore, more evidence is needed to assess the extent to which diseases interact, either at the level of populations or individuals, to amplify HIV risk.

Syndemics and Health Disparities: A Methodological Note

“…The extent to which these and other psychosocial and structural problems co-occur has typically been represented in the literature with the aid of Venn diagrams [13]; correlation matrices demonstrating nonzero, statistically significant values on the off-diagonals [16]; or similar matrices of unadjusted odds ratios [17]. Among the 40 studies included in the systematic review by Tsai & Burns [11], 27 (68%) demonstrated the co-occurrence of psychosocial and structural problems using one of these representations. Such analyses demonstrate that psychosocial and structural problems co-occur in at-risk populations -- thereby supporting one aspect of the theory of syndemics -- but do not necessarily implicate synergy or mutual causality.…”

“…As summarized by Tsai & Burns [11], most studies in the syndemics literature have not subjected their data to the empirical test described in Eq. (2).…”

“…These assumptions could potentially be justified on the basis of prior theory, but we are unaware of any studies in the literature that have made such appeals to theory. Furthermore, in the event that other patterns of findings are obtained for b 9 and b 10 (even assuming β 4 = β 5 = β 6 = 0), it is unclear whether the sum score specification can provide evidence in support of the theory of syndemics [11]. …”

“…For this reason, in the remainder of this essay we use the term “syndemic problems” to refer specifically to co-occurring and mutually enhancing psychosocial and structural problems, while retaining the more cumbersome term “psychosocial and structural problems” to refer to settings in which these problems have not necessarily been shown to be mutually enhancing or mutually causal. Most studies that have been conducted with the expressed aim of generating empirical support for the theory of syndemics have not operationalized the concept of disease interaction in a way that actually supports the theory’s predictions about mutually enhancing epidemics [11]. These findings are then frequently leveraged to argue that there is an evidence-based need for multi-component interventions that address multiple co-occurring psychosocial and structural problems in order to effectively address or prevent HIV-related health disparities [12].…”

The Utility of a Syndemic Framework in Understanding Chronic Disease Management Among HIV-Infected and Type 2 Diabetic Men Who Have Sex with Men

“…However, nearly one third of the sample had inadequate glycemic control, which was correlated with other markers of disease (e.g., hypertension, depression) and independently associated with substance use, high triglycerides, and unsuppressed HIV viral load. Although the small size of this sample precluded a full analysis of interactions between these potentially syndemic factors [37], our findings suggest that the management of co-occurring chronic conditions is complex and may be challenging for some patients and providers. Our findings also demonstrate the promise of syndemic theory to inform the design of future research that seeks to understand and improve health in this population.…”