Cost-Effectiveness of HIV Screening in Patients Older than 55 Years of Age

Context Although many HIV infections occur in older adults, national guidelines recommend screening only for persons age 13 to 64 years. Contribution This analysis suggests that screening persons age 55 to 75 years is reasonably cost-effective under the following circumstances: HIV prevalence is 0.1% or greater; a streamlined counseling process is implemented; and the person has a partner at risk for HIV infection. Implication This information on the cost-effectiveness of screening in older adults should inform decisions about expanding screening recommendations to older people. The Editors Recently revised HIV screening guidelines from the Centers for Disease Control and Prevention (CDC) recommend that all patients age 13 to 64 years in health care settings be tested (1). Previous work by our group (2) and others (35) has demonstrated that screening for HIV in younger patients is cost-effective even in relatively low-prevalence settings. For example, we found that screening 40-year-old persons costs less than $50000 per quality-adjusted life-year (QALY) when the prevalence of undiagnosed HIV infection is 0.05% (1 in 2000 persons) or higher (2). Although screening is cost-effective in younger age groups, approximately 19% of all people with AIDS in the United States were age 50 years or older when disease was diagnosed (6). The cost-effectiveness of screening older patients has not been evaluated and is uncertain. There are several reasons that screening patients older than age 55 years may be less cost-effective than screening younger persons. First, the prevalence of HIV, a major determinant of cost-effectiveness, is lower in older than in younger age groups (7). Second, treatment of HIV will be less cost-effective in older persons because the competing risk for death from other causes diminishes the absolute benefits of therapy. Third, if older patients have fewer sex partners, screening will be less economically attractive because reduction of HIV transmission is an important benefit of screening, and hence a determinant of cost-effectiveness (2). Finally, neither the effectiveness nor toxicity of highly active antiretroviral therapy (HAART) in patients age 55 to 75 years has been well studied; both could be less favorable than in younger patients (8). To assess the importance of these factors, we modified our previous cost-effectiveness model to assess the cost-effectiveness of HIV screening in persons older than age 55 years. Methods We estimated the health and economic effects of a program of voluntary HIV screening in patients age 55 to 75 years by using a decision model, following the recommendations of the Panel on Cost-Effectiveness in Health and Medicine. We did the analysis by using a societal perspective on health benefits and costs and applying a 3% annual discount rate (9). Decision Model We adapted a Markov model (10, 11) that was developed to assess the cost-effectiveness of voluntary HIV screening in health care settings (2) by using Decision Maker software, version 2007.0.1 (Pratt Medical Group, Boston, Massachusetts). The model tracked a cohort of older patients during their lifetime. Patients with prevalent HIV infection (asymptomatic or symptomatic HIV or AIDS) or those who were not infected could enter the model. Each month, patients who are not infected are at risk for HIV infection. Patients who have asymptomatic disease may progress to symptomatic HIV or remain in the asymptomatic health state. Patients who have symptomatic HIV infection may progress to an AIDS-defining condition or remain with symptomatic HIV. Patients with AIDS may either die from infection or remain with AIDS. Patients either were screened through a one-time voluntary HIV screening program or were followed without routine screening. Each month, the model assessed the patients' HIV status, whether their HIV status was identified, the clinical course of HIV disease, the costs and consequences of HIV transmission, and the costs and consequences of HAART for patients identified with HIV and eligible for treatment (Figure 1). Persons were also at risk for age- and sex-specific death not related to HIV. Probability estimates were based on high-quality published literature and expert clinical judgment (Table 1) (2, 9, 12156). Figure 1. The Markov model. The square node at the left represents the decision to screen or not to screen for HIV. The patient's health thereafter is simulated by a Markov model shown on the right. Patients may enter the model with prevalent HIV infection (asymptomatic or symptomatic HIV or AIDS) or they may not be infected. Each month, patients who are not infected are at risk for HIV infection. Patients who have asymptomatic disease may progress to symptomatic HIV or remain in the asymptomatic health state. Patients who have symptomatic HIV infection may progress to an AIDS-defining condition or remain with symptomatic HIV. Patients with AIDS may either die of infection or remain with AIDS. Each month, all patients may be identified either through a voluntary screening program in the HIV screening group or through symptom-based case findings in the symptomatic HIV and AIDS health states in both the HIV screening group and the no-screening group. Throughout the patients' lifetime, all patients are at risk for nonHIV-related death. Health states are further characterized by viral load level, CD4 count, and antiretroviral treatment history (not shown). HAART= highly active antiretroviral therapy. Table 1. Input Variables and Sources Patient Sample We assessed the cost-effectiveness of screening patients age 55 to 75 years who had an unknown HIV status in populations with a prevalence of unidentified HIV infection that varied from 0.1% to 1% (157). We estimated the incidence of HIV in age- and sex-specific strata based on previous models (18, 19). HIV Testing Patients who were not tested through an HIV screening program or who tested negative through screening could be selected for future testing through symptom-based case findings. We assumed that such case findings occurred only in patients with a CD4 count of 0.350109 cells/L or less and that the probability of identifying and testing for HIV increased as the CD4 count decreased. We incorporated standard HIV testing by using a serum enzyme-linked immunosorbent assay followed by confirmatory Western blot analysis. In our base-case analysis, patients received comprehensive pretest and posttest counseling with HIV testing. We explored the effects of streamlined counseling (abbreviated pretest counseling requirements) as recommended by the CDC (1) on HIV screening in sensitivity analyses. The benefits of testing and counseling accrued only to patients who received their test results and entered care. HIV Disease Progression and Treatment We modeled HIV disease progression by using HIV viral load copy number and CD4 count and drawing on natural history data (Table 1) (52, 77, 84). We assumed that treatment of HIV infection would adhere to published treatment guidelines, including appropriate prophylaxis and immunization (41, 42). We assumed that HAART was initiated when an identified HIV-infected patient's CD4 count decreased to 0.35109 cells/L or less. Once HAART was initiated, we modeled the possible increase in CD4 count, virologic suppression, treatment-related toxicity, and virologic rebound. We assumed that patients with drug-related adverse effects switched to a new regimen and had the same probability of achieving suppression as they did with the initial regimen. In contrast, we assumed that patients who had virologic failure and were identified through viral load testing were switched to a new regimen with a reduced likelihood of achieving virologic suppression (Table 1). We assumed that after being treated with 3 successive antiretroviral regimens, a patient could achieve only partial virologic suppression because of multidrug resistance. We assessed varying assumptions about the efficacy of treatment of such patients in sensitivity analysis. Effectiveness and Toxicity of HAART in Patients Older Than Age 55 Years Substantial uncertainty exists about the effectiveness of HAART and the course of HIV infection among older patients. Although patients older than age 55 years may have higher rates of virologic suppression (perhaps because of better adherence or altered pharmacodynamics), the evidence about immunologic effects in patients in this sample is inconsistent. Although several studies have suggested that older patients have a longer time to CD4 reconstitution after starting HAART (8991, 94, 98), other studies have found no differences or differences in the first year only (8, 92, 93, 9597). Studies have similarly differed about whether older age is an independent risk factor for disease progression (90, 158). The evidence about the toxicity of antiretrovirals in older patients is even more limited. Although there are many reasons to suspect that older patients do not tolerate antiretrovirals as well as younger patients (such as cardiovascular and hepatic events), the evidence for this assertion is still weak (8, 91, 94, 96). We approached the modeling of HAART effectiveness and toxicity in patients older than age 55 years, recognizing that the evidence for age effects is generally based on observational studies that are often small and with considerable potential for residual confounding. To address the uncertainty around these age effects and explore their potential impact, our base-case model assumed no difference in antiretroviral efficacy for older patients, but we included specific scenarios in which we modeled 3 effects that may be related to older age: greater failure rates with HAART, greater treatment-limiting toxicities, and greater age-specific death not related to AIDS. Transmission of HIV We included the potential costs and health benefits associated with transmission of HIV from an infected individual to their sexual partner