摘要：Objectives. We compared the influence of substance abuse with that of other comorbidities (e.g., anxiety, HIV) among people with mood disorder (N = 129 524) to explore risk factors for psychiatric hospitalization and early readmission within 3 months of discharge. Methods. After linking Medicaid claims data in 5 states (California, Florida, New Jersey, New York, and Texas) to community-level information, we used logistic and Cox regression to examine hospitalization risk factors. Results. Twenty-four percent of beneficiaries with mood disorder were hospitalized. Of these, 24% were rehospitalized after discharge. Those with comorbid substance abuse accounted for 36% of all baseline hospitalizations and half of all readmissions. Conclusions. Results highlight the need for increased and sustained funding for the treatment of comorbid substance abuse and mood disorder, and for enhanced partnership between mental health and substance abuse professionals. Mood disorders are currently the leading cause of psychiatric hospitalization. 1 , 2 About 46% of all psychiatric inpatients in Maryland state general hospitals, 1 for example, are admitted for major depressive disorder or bipolar disorder, and within a year of discharge, between 20% and 50% are likely to be readmitted. 3 – 5 Many researchers have concluded, however, that few clinical characteristics can reliably predict either hospitalization or rehospitalization. 3 , 4 Several studies suggest that comorbidity with substance abuse is associated with the first lifetime hospitalization for mood disorder, 2 increased risk of psychiatric hospitalization more generally, 6 and readmission after discharge. 7 Most American studies on the topic, however, have used small to midsize local samples, and findings from much larger investigations using Danish case registers, 7 for example, or information on US military populations 8 may not generalize to the US general population or to low-income people such as those receiving Medicaid. There do not appear to be any large-scale American studies comparing the role of substance abuse and other factors in either hospitalization or early readmission among Medicaid beneficiaries with mood disorder, even though Medicaid is the largest payer (covering 44% of all costs) of public mental health services. 9 It is the only insurance plan available to many low-income persons, who rely on it exclusively for coverage of outpatient mental health or substance abuse treatment. By linking 1999 to 2000 Medicaid claims data in 5 US states (California, Florida, New Jersey, New York, and Texas) to data on neighborhood characteristics (from the US Census at the zip code level and from Area Resource Files 10 at the county level), we examined hospitalization for mood disorder and readmission within 3 months of discharge. After adjusting for the effects of gender, ethnicity, age, location, community characteristics, and dual eligibility with Medicare, we (1) investigated the influence of substance abuse on hospitalization for mood disorder, (2) compared the influence of substance abuse with that of other co-occurring conditions (anxiety, personality, or major medical disorder), and (3) assessed whether the influence of substance abuse was greater with major depressive disorder or bipolar disorder. Research on comorbidity in mood disorder has yielded 3 major conclusions. 2 – 4 , 11 – 24 First, comorbid substance abuse can have harmful negative consequences, including exacerbation of mood disorders, nonadherence to psychiatric medications, poor response to prescription drugs, and physical illness (e.g., liver disease). Second, anxiety and personality disorders contribute to poor response to treatment and increased risk of psychiatric hospitalization, and substance abuse can co-occur with them. Third, for 25% to 70% of persons with mood disorder who also have 1 or more of these comorbid conditions, diagnosis and treatment is much more complex in both inpatient and outpatient settings. Apart from comorbidity, sociodemographic characteristics can increase the likelihood of hospitalization or readmission for mood disorder; their influence must be examined in studies predicting the use of hospital care from substance abuse or other risk factors. The evidence, however, is mixed. Some researchers have found that people initially hospitalized at a younger age are more likely to be rehospitalized later, 25 but others have failed to find substantial differences. 3 Similarly, Herrell et al. 8 found that Blacks were less likely than were Whites to be hospitalized for mood disorder, but other studies suggest that psychiatric hospital admission in general is more common among Blacks than Whites. 26 , 27 Similar to sociodemographic characteristics and comorbidity with substance abuse or other psychiatric disorders, medical comorbidity can affect hospitalization and readmission outcomes for mood disorder. People with mood disorders are more likely than is the general population to have health problems. 28 – 31 The side effects of medications, difficulty accessing high-quality medical care, and unhealthful behaviors such as poor diet, lack of exercise, substance abuse, and smoking all increase the risk for cardiovascular disorders, cancer, hypertension, diabetes, and hyperlipidemia. Better outpatient treatment of these and other physical illnesses is needed to prevent hospitalization, prolong life, and contribute to overall well-being. In short, there have been a variety of studies on hospitalization or readmission for mood disorder, but in the United States they are relatively small in scale, are typically cross-sectional and descriptive rather than longitudinal and predictive in nature, and they fail to focus on large numbers of low-income people who rely on Medicaid-funded services. Our study appears to be the first to examine the role of substance abuse and other risk factors in psychiatric hospitalization and readmission using a multistate sample of Medicaid beneficiaries with major depressive disorder or bipolar disorder. It also appears to be among the first to compare the impacts of substance abuse and of psychiatric or medical comorbidities after control for such local influences as median income and unemployment rate, as well as a wide variety of other factors. On the basis of published research, we hypothesized that substance abuse increases risk for both hospital admission and readmission, even after inclusion of control variables. In addition, we tested the null hypothesis that substance abuse is equally influential in admission and readmission for both major depressive disorder and bipolar disorder, as well as the alternative hypothesis that drug or alcohol use is more influential in one or the other mood disorder—for example, because of the greater biological basis of bipolar disorder. 32 Finally, we tested the null hypothesis that, after adjustment for other factors, substance abuse comorbidity is no more influential than other types of comorbidity. Because there was no strong evidence or theoretical basis for hypothesizing that substance abuse had a greater impact than did other risk factors on hospitalization for mood disorder, we chose an open-ended exploration of the various factors’ impacts.
