Background: Mounting evidence of high HIV prevalence rates among persons with serious mental illness underscores the importance of identifying and treating this population in order to prevent morbidity, mortality and the spread of the disease. Continual monitoring of services and costs is important for public health purposes to insure that persons with serious mental illness receive care for their HIV disorder that is at least comparable to those with HIV only and that the care is considered to be of equal quality. Aim of Study: This current study examines 2003 Medicaid expenditures associated with the treatment of adults with both serious mental illness and HIV, compared to those with HIV and serious mental illness only. The degree to which the occurrences of co-morbid conditions affect overall expenditures is examined, providing the first published co-morbidity expenditure ratios showing the additional cost burden associated with having these dual disorders. Also, changes in the composition of service costs for the co-morbid population are examined before and after the advent of newer antiretroviral and atypical antipsychotic medications. Methods: Study participants were adult Medicaid recipients age 1964 with serious mental illness and Hill receiving services from a large urban city program in 2003. The expenditures were derived from Medicaid claims records. Differences between groups were compared using Chi-square and ANOVA tests of significance. To determine the relative cost burden of having a co-morbid versus a single disorder, a co-morbidity expenditure ratio was constructed using the total expenditure per person of those with a co-morbid disorder compared to the total expenditures of those with SMI-only and HIV-only. In order to determine the relative change in inpatient, outpatient and pharmacy service costs, the composition of service costs in 1996 is compared to the service cost composition in 2003 using the share of total costs that each service contributes. Results: In 2003, 788 persons with both SMI and HIV had the highest treatment expenditures at $23,842 per person followed by 2984 persons with HIV-only at $13,183, while the SMI-only group of 19,664 individuals was $11,860 per person. The comparison group had expenditures of $4,793 per person. The co-morbidity expenditure ratio in 2003 for the co-morbid population compared to the SMI-only group was 2.0 and 1.8 for the co-morbid population to the HIV-only population. Extensive redistribution of cost occurred between service categories in the co-morbid group between 1996 and 2003. The share of inpatient cost was reduced from 64% of total costs in 1996 to 30% of total cost in 2003. Conversely, the outpatient cost share increased from 17% of total costs in 1996 to 42% of total costs in 2003 as did the pharmacy share, which rose from 19% of total costs in 1996 to 27% of total costs in 2003. Discussion: Consistent with previous studies, the co-morbid group is a costly population with respect to treatment, despite the fact that inpatient care has decreased. The co-morbidity expenditure analysis indicates little cost saving associated with treating individuals with the co-morbid conditions compared to the cost of treating either conditions separately. This may suggest a lack of coordination or effective care management in the current system warranting further investigation. Also, we find no difference in the percent of the co-morbid population receiving HIV medication compared to the HIV population alone. This suggests that the co-morbid SMI population was being treated similarly to the HIV only group for their HIV disorders. Finally, though all groups had changes between 1996 and 2003 in the proportion of expenditures allocated to each of the service categories, the redistribution of cost between inpatient and outpatient care was the greatest in the co-morbid group. Implications for Future Research: Although the study data suggests that individuals with both HIV and serious mental illness are receiving similar treatment for their HIV disorder as those with HIV alone, a concern that requires further investigation is the finding that HAART treatment is being used by less than 50% of the co-morbid and HIV only study population. Further investigation is required to determine the reason for the relatively low utilization of HAART medications in both HIV groups. Also, the use of a co-morbidity expenditure ratio offers a promising approach for comparing the cost burden associated with multiple disorders.
