Riley et al. Respond to “Co-occurring Health Conditions and Life Challenges”

American Journal of Epidemiology a The Author 2011. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. Vol. 174, No. 5 DOI: 10.1093/aje/kwr208 Advance Access publication: July 11, 2011 Response to Invited Commentary Riley et al. Respond to ‘‘Co-occurring Health Conditions and Life Challenges’’ Elise D. Riley*, James L. Sorensen, Kelly Moore, Jacqueline P. Tulsky, David R. Bangsberg, and Torsten B. Neilands Initially submitted May 10, 2011; accepted for publication May 25, 2011. We appreciate the insightful commentary provided by Dr. Coughlin (1) that accompanies our article (2) on the overall health status of homeless and unstably housed women. In particular, we commend the way in which Dr. Coughlin frames the challenges surrounding comorbidity within this popu- lation. As he points out, the burden of mental and physical illness is extremely high among homeless women, and we agree that more attention should be given to the presence of trauma-related disorders when considering the conditions impacting their health and well-being. Each condition does not occur in isolation; rather, the conditions influence each other as well as the risk for developing additional comorbidities. Co-occurring disorders are less often studied than specific conditions for a variety of reasons; among them are the chal- lenges of valid measurement and deduction of meaningful results. For example, issues of nonindependence, confound- ing, and interaction between the conditions must be taken into account (3). An approach commonly used to measure comor- bidity is a sum of the conditions present; however, unless weighted, it will assume the same influence from conditions that have different impacts on health, will not account for interaction between conditions, may be susceptible to ceiling effects of some condition measurements (4), and may change over time (5). Similarly, assessing the influences of comor- bidity on a separate outcome is complicated. Simple adjust- ment approaches, such as using multiple interaction terms, render the interpretation of results challenging, if not unten- able. Conversely, if adjustment is not made for the influences of comorbidity, results may inappropriately assign causal ef- fect to a single condition, which may result in negative clin- ical implications (6). The overwhelming number of interrelated comorbidities among unstably housed persons creates a paradox. A better understanding of comorbid conditions is needed to improve prevention, intervention, and effective treatments, yet their complex associations make interpretation of their combined and condition-specific effects a formidable challenge. We join Dr. Coughlin in calling for more attention to comorbid con- ditions among unstably housed individuals. We further sug- gest that this call embrace a combination of approaches, including the assessment of specific conditions, combinations of co-occurring conditions, and indices of overall health sta- tus, as multiple perspectives will offer a more comprehensive understanding of this complicated situation. By assessing overall health status, our paper offers a broad view of factors that influence the total burden of illness that, by its nature, integrates the effects of all disorders present in an individual (including interactive effects). As the objective of our study was to measure overall health status, analyses did not include specific conditions as outcomes of interest, nor did they consider influences of specific conditions as expo- sure variables because the effects were part of the outcome measure. Overall, this analysis offers a different type of in- formation from those considering specific health conditions. For instance, although the assessment of 1 or multiple co- occurring conditions may provide guidance for diagnosis and treatment, understanding influences on overall health status provides context for a treatment plan. In our study, unmet subsistence needs had a stronger influence on overall health than a variety of previously established predictors and, thus, the implication is that the treatment plans offered may not be as effective at improving overall health until an unstably housed woman’s subsistence needs are met. We look forward to considering this analysis in combination with our forth- coming studies on specific mental health conditions. In addi- tion, we hope that these results can be used with other condition-specific investigations to inform health-care deliv- ery, research, and policies that improve the health of home- less and unstably housed women. ACKNOWLEDGMENTS Author affiliations: Department of Medicine, University of California, San Francisco, California (Elise D. Riley, Am J Epidemiol. 2011;174(5):526–527 Downloaded from http://aje.oxfordjournals.org/ at University of California, San Francisco on January 20, 2016 * Correspondence to Dr. Elise Riley, 1001 Potrero Avenue, UCSF Mailbox 0874, San Francisco, CA 94143-0874 (e-mail: eriley@ epi-center.ucsf.edu).