We used data from the USHER Trial to inform a critical, policy-relevant question regarding the revised HIV screening guidelines: does the economic efficiency of HIV screening depend on how the screening programs are designed and staffed? We found that counselor-based, compared to provider-based, routine HIV screening in an emergency department setting is cost-effective, as assessed by contemporary criteria for cost-effectiveness 
. With very similar cost-effectiveness ratios for the two rapid, point-of-care screening programs, the results also suggest roughly the same return on investment from counselor-based and provider-based screening. Why? Because, the mechanics of the screening program have little impact on either long-term costs or long-term benefits. What drives both costs and benefits in the long-run is the pathway of care and treatment triggered whenever and however a case of infection is detected and successfully linked to care. Consequently, whichever program maximizes the total number of patients linked to care is the better choice. Findings in favor of counselor-based screening were robust under assumptions intended to generalize our results beyond the USHER Trial setting including variations in undiagnosed HIV prevalence and programmatic costs.
Our results are consistent with previous studies linking the cost-effectiveness of HIV testing to the costs and benefits of downstream HIV care 
. Those studies are founded upon the grounds that HIV-infected individuals have an enormous amount of health benefit to gain from routine access to HIV care 
– benefits that could not be realized without an HIV diagnosis. Cost-effectiveness studies also demonstrate the relative insensitivity of those findings to HIV screening costs 
; the fact that screening costs can increase 10-fold without impacting cost-effectiveness results is due to the comparatively small component of screening costs in the overall costs of care that HIV-infected patients ultimately generate. More recent work has reported that, on a national level, the revised HIV screening guidelines will cost $2.7 billion over the next 5 years; only 18% of that budget increase is due to testing costs 
Although testing costs have little influence on the cost-effectiveness ratios, such costs are critical to the budgetary planning of screening program development. Indeed, a cost-effective program must also be affordable for it to be effectively implemented, and the affordability of new counseling personnel must be seriously considered. Our findings regarding the resource utilization required of emergency medicine personnel to conduct HIV testing were consistent with a survey of HIV screening costs in 45 hospitals 
. We note that the approximate 5 minutes required for “test offer” is likely an overestimate for most other settings now that laws requiring time-intensive, written informed consent for HIV screening have been amended in most states. Among the biggest time and cost commitments in the provider arm of the USHER Trial was the delivery of reactive results by the attending physician. Though these events are relatively rare in any domestic screening program, it should be recognized that newly diagnosed HIV-infected patients will require due time and attention. This time may be hard for a busy emergency department staff to allocate but is essential to a clinically sensitive screening environment.
These results hinge upon the practical truth that in most ED settings, current staff are stretched too thin to perform point-of-care rapid HIV tests on all ED patients and to provide the spectrum of support services that such testing would require. Hiring of relatively inexpensive personnel, like HIV counselors, to improve screening coverage is worth the investment. However, if the current ED personnel have the capacity to increase coverage – such that screening program participation approaches that of the counselors – the value of additional personnel is diminished.
Results are also sensitive to the capacity of ED providers to “target” screen their patients; that is, the providers' ability to identify and test those patients at highest risk for HIV infection. While providers may excel at recognizing and testing patients who present with symptoms consistent with an AIDS-defining illness, such clinical presentations are relatively rare. Previous reports have demonstrated that providers often do not routinely nor comfortably inquire about sexual and substance use habits 
. Some findings from the USHER Trial suggest that providers preferentially tested younger patients: the rate of test offer was similar across all ages in the counselor arm, but decreased with increasing age in the provider arm. However, among the factors measured, the trial data did not suggest differences in provider test offer rates, stratified by subjects' self-reported high sexual or substance abuse risk; differences in provider offer rates may well exist among unmeasured factors 
Placing program efficacy and efficiency outcomes side-by-side highlights important trade-offs demonstrated in the USHER Trial. Provider-based screening is cheaper on a per result basis. However, weaving HIV screening activities into the demands on the time of an already overstretched staff has its downsides – fewer patients may be tested. In contrast, hiring dedicated counselors for these activities ensures that a greater number of patients actually receive an HIV test but does so at greater costs. Our cost-effectiveness results suggest that there is good value to be obtained by investing in larger, counselor-based HIV case identification.
Notably, the efficacy-versus-efficiency tradeoff may become less stark in the future. With streamlined consent processes and advancing technology for non-rapid HIV tests, it may soon be feasible to HIV screen all phlebotomized emergency department patients 
without ancillary staff 
. That such programs are still hindered by lower rates of linkage to care speaks to the continued need for counselor support and the applicability of our results.
Our results have several noteworthy limitations. First, Massachusetts remains one of three states where laws requiring written informed consent for HIV testing persist. Per person testing costs in both trial arms may be higher than those observed in states with more streamlined testing. However, all of our results point to the robustness of our findings in the face of varying program costs.
Second, we employed data obtained directly from the USHER Trial to develop base case estimates of test offer, acceptance and resource utilization parameters for both the Provider and Counselor strategies. Importantly, a single base case value of 0.4% was estimated for the prevalence of undetected HIV, and this value was applied to both the Provider and Counselor strategies in our analysis. In the base case, we chose not to make use of the difference in new HIV diagnoses observed in the two arms of the USHER Trial (7/631 in the provider arm versus 0/1371 in the counselor arm). We made this choice because we intended to examine the cost-effectiveness of alternative HIV screening strategies when applied to a single population of ED clients, not to two differing populations of such clients. Since the USHER Trial findings suggested some degree of targeting in the provider arm, we did conduct extensive sensitivity analyses assuming different prevalence values for patients served by providers and patients served by counselors. We also examined other parameters describing areas where programs may function differently, including rates of test offer and acceptance. Because the cost-effectiveness results were sensitive to the difference in prevalence by testing strategy, we urge readers to interpret our conclusions regarding the comparative value of the Counselor strategy – and the important impact of the potential for providers to target test – with caution.
Finally, our analysis does not capture the large potential impact of improved case detection on secondary HIV transmission. Our failure to estimate ART's preventive benefits to the broader population remains a handicap that almost certainly understates both the health benefits and cost-effectiveness findings reported here. We believe that our modeling approach can be justified on the grounds that it is conservative – i.e., taking the preventive benefits of ART into consideration would only serve to strengthen the already-favorable findings. However, we also acknowledge that there is an important qualitative difference between an attractive incremental cost-effectiveness ratio of ~$60k/QALY and an even-more-attractive ratio several tens of thousands of dollars smaller and that this difference may, in fact, result in policy differences in some settings. Therefore, incorporating population-level transmission benefits into future analyses represents an important next step.
We found that HIV screening in the emergency department setting – whether conducted by emergency department staff or dedicated counselors – resulted in screening costs ranging from $8–$31 per test result received. While provider-based screening was cheaper on a per result-received basis, counselor-based testing ultimately screened more patients and conferred sufficient value ($64,500/QALY) to justify the additional outlay. However, cost-effectiveness does not imply affordability. In settings where resources may be insufficient to support the implementation of full-scale, counselor-based screening, provider-based approaches will continue to represent an excellent, cost-effective alternative to no screening at all.