A systematic comparison of additive and interaction approaches to modeling the effects of syndemic problems on HIV outcomes in South Africa

doi:10.1007/s10865-024-00517-y

Comparative Study

. 2024 Dec;47(6):1028-1039.

doi: 10.1007/s10865-024-00517-y. Epub 2024 Sep 21.

A systematic comparison of additive and interaction approaches to modeling the effects of syndemic problems on HIV outcomes in South Africa

Jasper S Lee^{1

2}, Sierra A Bainter³, Alexander C Tsai^{4

5

6}, Lena S Andersen⁷, Amelia M Stanton⁸, Jessica F Magidson⁹, Ashraf Kagee¹⁰, Julian May¹¹, John A Joska¹², Conall O'Cleirigh^{13

4}, Steven A Safren³

Affiliations

¹ Department of Psychiatry, Behavioral Medicine Program, Massachusetts General Hospital, One Bowdoin Square 9th Floor, Boston, MA, 02114, USA. jlee333@mgh.harvard.edu.
² Department of Psychiatry, Harvard Medical School, Boston, MA, USA. jlee333@mgh.harvard.edu.
³ Department of Psychology, University of Miami, Coral Gables, Florida, USA.
⁴ Department of Psychiatry, Harvard Medical School, Boston, MA, USA.
⁵ Center for Global Health and Mongan Institute, Massachusetts General Hospital, Boston, MA, USA.
⁶ Harvard Medical School, Boston, MA, USA.
⁷ Department of Public Health, Global Health Section, University of Copenhagen, Copenhagen, Denmark.
⁸ Department of Psychological and Brain Sciences, Boston University, Boston, MA, USA.
⁹ Department of Psychology, University of Maryland, College Park, MD, USA.
¹⁰ Department of Psychology, Stellenbosch University, Western Cape, Stellenbosch, South Africa.
¹¹ Centre of Excellence in Food Security, University of the Western Cape, Cape Town, South Africa.
¹² Division of Neuropsychiatry, Department of Psychiatry and Mental Health, HIV Mental Health Research Unit, Neuroscience Institute, University of Cape Town, Cape Town, South Africa.
¹³ Department of Psychiatry, Behavioral Medicine Program, Massachusetts General Hospital, One Bowdoin Square 9th Floor, Boston, MA, 02114, USA.

PMID: 39306630
PMCID: PMC11499001 (available on 2025-12-01)
DOI: 10.1007/s10865-024-00517-y

Comparative Study

A systematic comparison of additive and interaction approaches to modeling the effects of syndemic problems on HIV outcomes in South Africa

Jasper S Lee et al. J Behav Med. 2024 Dec.

. 2024 Dec;47(6):1028-1039.

doi: 10.1007/s10865-024-00517-y. Epub 2024 Sep 21.

Authors

Affiliations

¹ Department of Psychiatry, Behavioral Medicine Program, Massachusetts General Hospital, One Bowdoin Square 9th Floor, Boston, MA, 02114, USA. jlee333@mgh.harvard.edu.
² Department of Psychiatry, Harvard Medical School, Boston, MA, USA. jlee333@mgh.harvard.edu.
³ Department of Psychology, University of Miami, Coral Gables, Florida, USA.
⁴ Department of Psychiatry, Harvard Medical School, Boston, MA, USA.
⁵ Center for Global Health and Mongan Institute, Massachusetts General Hospital, Boston, MA, USA.
⁶ Harvard Medical School, Boston, MA, USA.
⁷ Department of Public Health, Global Health Section, University of Copenhagen, Copenhagen, Denmark.
⁸ Department of Psychological and Brain Sciences, Boston University, Boston, MA, USA.
⁹ Department of Psychology, University of Maryland, College Park, MD, USA.
¹⁰ Department of Psychology, Stellenbosch University, Western Cape, Stellenbosch, South Africa.
¹¹ Centre of Excellence in Food Security, University of the Western Cape, Cape Town, South Africa.
¹² Division of Neuropsychiatry, Department of Psychiatry and Mental Health, HIV Mental Health Research Unit, Neuroscience Institute, University of Cape Town, Cape Town, South Africa.
¹³ Department of Psychiatry, Behavioral Medicine Program, Massachusetts General Hospital, One Bowdoin Square 9th Floor, Boston, MA, 02114, USA.

PMID: 39306630
PMCID: PMC11499001 (available on 2025-12-01)
DOI: 10.1007/s10865-024-00517-y

Abstract

Much of the research on the effects of syndemics on HIV outcomes has utilized an additive approach. However, interaction effects may better account for syndemic synergy than an additive approach, but it remains difficult to specify interaction effects without empirical guidance. We sought to systematically compare additive and interaction effects approaches to modeling the effects of syndemic problems on antiretroviral therapy (ART) using empirically specified interaction terms. Participants were 194 people with HIV (PWH) who received HIV care in Khayelitsha, South Africa. In a series of linear regression models, we examined ten syndemic problems: depression, alcohol use, intimate partner violence (IPV), post-traumatic stress, social anxiety, substance use, food insecurity, poverty, housing instability, and structural barriers to care. Depression, substance use, and food insecurity were selected for interaction terms based on a prior network analysis, which found these problems to be most central. The additive models did not produce statistically significant findings. However, the interaction effects models yielded significant interaction terms in both the full model and a parsimonious model. There was a statistically significant effect of the interaction between depression and food insecurity on ART adherence (b = 0.04, Robust SE = 0.02, 95%CI [0.001-0.08], p = .012). This pattern of results was replicated in the parsimonious model. Findings suggest that when feasible, interaction effects approaches may be a helpful syndemic modeling technique. Results may inform future intervention targets, such as depression and food insecurity, and the importance of addressing both structural and psychosocial syndemic problems.

Keywords: ART adherence; Depression; Food insecurity; HIV; Interaction effects; Syndemics.

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Conflict of interest statement

Conflicts of interest Dr. Safren receives royalties for books published by Oxford University Press, Springer/Humana Press, and Guilford Publications. Dr. Tsai receives an honorarium from Elsevier for his work as Co-Editor in Chief of the Elsevier-owned journal SSM - Mental Health.

References

1. Aiken LS, West SG, & Reno RR (1991). Multiple regression: Testing and interpreting interactions. sage.
1. Biello KB, Oldenburg CE, Safren SA, Rosenberger JG, Novak DS, Mayer KH, & Mimiaga MJ (2016). Multiple syndemic psychosocial factors are associated with reduced engagement in HIV care among a multinational, online sample of HIV-infected MSM in Latin America. AIDS Care, 28, 84–91. 10.10800/9540121.2016.1146205 - DOI - PMC - PubMed
1. Blashill AJ, Bedoya CA, Mayer KH, O’Cleirigh C, Pinkston MM, Remmert JE, et al. (2015). Psychosocial syndemics are additively associated with worse ART adherence in HIV-infected individuals. AIDS and Behavior, 19, 981–986. 10.1007/s10461-014-0925-6 - DOI - PMC - PubMed
1. Blashill AJ, Brady JP, Rooney BM, Rodriguez-Diaz CE, Horvath KJ, Blumenthal J, et al. (2020). Syndemics and the PrEP cascade: results from a sample of young latino men who have sex with men. Archives of Sexual Behavior, 49, 125–135. 10.1007/s10508-019-01470-7 - DOI - PMC - PubMed
1. Borsboom D, & Cramer AO (2013). Network analysis: An integrative approach to the structure of psychopathology. Annual Review of Clinical Psychology, 9, 91–121. - PubMed

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[1] Aiken LS, West SG, & Reno RR (1991). Multiple regression: Testing and interpreting interactions. sage.

[2] Aiken LS, West SG, & Reno RR (1991). Multiple regression: Testing and interpreting interactions. sage.

[3] Biello KB, Oldenburg CE, Safren SA, Rosenberger JG, Novak DS, Mayer KH, & Mimiaga MJ (2016). Multiple syndemic psychosocial factors are associated with reduced engagement in HIV care among a multinational, online sample of HIV-infected MSM in Latin America. AIDS Care, 28, 84–91. 10.10800/9540121.2016.1146205 - DOI - PMC - PubMed

[4] Biello KB, Oldenburg CE, Safren SA, Rosenberger JG, Novak DS, Mayer KH, & Mimiaga MJ (2016). Multiple syndemic psychosocial factors are associated with reduced engagement in HIV care among a multinational, online sample of HIV-infected MSM in Latin America. AIDS Care, 28, 84–91. 10.10800/9540121.2016.1146205 - DOI - PMC - PubMed

[5] Blashill AJ, Bedoya CA, Mayer KH, O’Cleirigh C, Pinkston MM, Remmert JE, et al. (2015). Psychosocial syndemics are additively associated with worse ART adherence in HIV-infected individuals. AIDS and Behavior, 19, 981–986. 10.1007/s10461-014-0925-6 - DOI - PMC - PubMed

[6] Blashill AJ, Bedoya CA, Mayer KH, O’Cleirigh C, Pinkston MM, Remmert JE, et al. (2015). Psychosocial syndemics are additively associated with worse ART adherence in HIV-infected individuals. AIDS and Behavior, 19, 981–986. 10.1007/s10461-014-0925-6 - DOI - PMC - PubMed

[7] Blashill AJ, Brady JP, Rooney BM, Rodriguez-Diaz CE, Horvath KJ, Blumenthal J, et al. (2020). Syndemics and the PrEP cascade: results from a sample of young latino men who have sex with men. Archives of Sexual Behavior, 49, 125–135. 10.1007/s10508-019-01470-7 - DOI - PMC - PubMed

[8] Blashill AJ, Brady JP, Rooney BM, Rodriguez-Diaz CE, Horvath KJ, Blumenthal J, et al. (2020). Syndemics and the PrEP cascade: results from a sample of young latino men who have sex with men. Archives of Sexual Behavior, 49, 125–135. 10.1007/s10508-019-01470-7 - DOI - PMC - PubMed

[9] Borsboom D, & Cramer AO (2013). Network analysis: An integrative approach to the structure of psychopathology. Annual Review of Clinical Psychology, 9, 91–121. - PubMed

[10] Borsboom D, & Cramer AO (2013). Network analysis: An integrative approach to the structure of psychopathology. Annual Review of Clinical Psychology, 9, 91–121. - PubMed

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A systematic comparison of additive and interaction approaches to modeling the effects of syndemic problems on HIV outcomes in South Africa

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A systematic comparison of additive and interaction approaches to modeling the effects of syndemic problems on HIV outcomes in South Africa

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