To our knowledge, this is the first study to estimate the population effects of insurance coverage on the use of health services and ART among community-recruited HIV-positive unstably housed individuals. We conclude that insurance continuity and, to a lesser extent, increasing durations of observed coverage were positively associated with increased health services use in this population. Ninety-five percent of study participants reported some type of insurance during at least one interview and 28% had a break in coverage. These results support conclusions reached by Sommers et al. regarding the retention of Medicaid and SCHIP recipients, namely that enrolling eligible persons is not the primary program limitation, rather that public insurance programs need to retain those enrolled (Sommers 2007
). Conducted in San Francisco, this study represents the impact of insurance coverage among a high-need population in a resource-rich area. Therefore, we would expect that ambulatory care use and ART use among persons with one year of continuous coverage would be at least 3 times higher than those without insurance coverage ( and ), and likely more in resource-poor areas where the uninsured have fewer options (Buchmueller et al. 2005
Our finding that consistent and longer durations of insurance coverage did not result in lower odds of inpatient hospitalization () is consistent with earlier studies (Buchmueller et al. 2005
; Hahn 1994
; Long, Marquis, and Rodgers 1998
). Taken together, these results suggest that while inpatient care is suboptimal, it is necessary, and persons without insurance are unable to receive either necessary or optimal care. This hypothesis is supported by data suggesting that while Medicaid recipients access services more frequently, their uninsured counterparts experience poorer health status resulting in higher service need once care is finally sought (Gilman, and Green 2008
Similar to inpatient care, the findings presented here do not support the hypothesis that consistent and longer durations of insurance coverage result in lower odds of emergency department use. This pattern of care seeking among insured patients may reflect an inability to obtain timely appointments with primary care providers (Newton et al. 2008
) or difficulties in establishing clinically appropriate care patterns (Sudano, and Baker 2003
). This pattern of care may also reflect recent findings by Rodriguez et al., which suggest that emergency department visits are often made to address hunger, shelter, and safety rather than medical need (Rodriguez et al. 2009
). While the current study adjusted for competing and unmet need during each 3-month interval, it did not account for need at the time of emergency department visits. Future studies among impoverished people may be strengthened by including data regarding both medical and social reasons for each emergency department visit.
Confounding variables included in the final treatment models were CD4 cell count, viral load, ART use in the previous quarter, primary care use in the previous quarter, insurance in the previous quarter, age, monthly income, year of observation and crack cocaine withdrawal. A failure to include factors such as heroin withdrawal or heavy alcohol use in the final treatment model does not indicate that these issues are unimportant with regard to services use; rather it indicates that, on a population-level, these issues do not confound the association between insurance status and services use. The confounding of the association between insurance and the use of services by cocaine withdrawal suggests that drug treatment and attempts to reduce drug-related withdrawal may lead to improved levels of health service use and thus improved health among HIV-infected unstably housed persons. Additionally, after controlling for changes in insurance, withdrawal and income, neither race nor gender confounded the relationship between insurance status and health services use. This result extends earlier findings indicating that racial minorities and women experience the least optimal health services use among HIV-infected persons (Shapiro et al. 1999
) by showing that, when adjustment is made for confounding due to competing needs which may disproportionately effect people of color and women, ethnicity and gender have less influence on health services use.
The results of this study should be considered in light of potential limitations. First, study participants may have underreported behaviors such as drug use, due to social desirability, or health services use, due to complexities or uncertainty in the system. However, in this case, we would expect results to have been biased toward the null, indicating that effects are at least as strong as those reported here. Second, restricting the sample population to persons with 5 consecutive interviews may have biased the population to higher functioning individuals. Comparisons of persons included and not included failed to show significant differences, suggesting that any resulting bias was minimal; however, it is possible that unmeasured differences exist. Third, we attempted to minimize biases related to obtaining insurance during a hospital visit by adjusting for insurance and health services in the previous quarter; however, residual confounding may exist. Finally, regardless of insurance status, there are a variety of factors that may predispose some individuals to use more services than others (Gelberg et al. 2000
). By adjusting for insurance and health service use in the previous quarter, we minimized potential confounding due to such predisposing factors. Strengths of this study include a reproducible community-based sample of unstably housed persons, including those in and outside of the health care system; frequent data collection over a 12-month observation period; detailed information on a broad spectrum of issues specific to marginalized populations; and statistical control for time-dependent confounding.
Economic crises that lead to homelessness often reorder priorities among HIV-infected persons, deemphasizing consistent medical care (Riley et al. 2007
). The results presented here suggest that consistent insurance may counteract some of these barriers and, while the impact of inconsistent insurance is not as strong, it is still effective. Given the array of competing and unmet needs in this population, maintaining consistent health insurance, much like consistent medical care, is not likely to be a priority for many unstably housed individuals. The seemingly insignificant nature of insurance coverage in the context of poverty, and additional difficulties such as being located for insurance recertification when an individual is homeless, suggest the need for health care policy efforts aimed at decreasing barriers to consistent coverage in vulnerable populations.
Costs and benefits associated with extending health insurance coverage depend on the ways in which health insurance affects the utilization of medical care, and these influences are expected to vary across different populations (Buchmueller et al. 2005
). The results presented herein indicate that for HIV-infected unstably housed persons, a 3-fold potential increase in use of ambulatory services and ART are expected when insurance coverage is consistent. Sustained use of ART is the strongest predictor of survival among HIV-infected unstably housed persons (Riley et al. 2005
), and increased costs associated with initiating antiretroviral therapy are offset by marked decreases in costs for overall HIV care (Hill, and Gebo 2007
; Merito et al. 2005
). Thus, these results suggest that, despite a host of competing needs in this population, consistent insurance coverage strongly influences factors with the most potential to reduce morbidity and mortality as well as the associated costs among unstably housed persons.