For the first time, HIDES I has demonstrated an effective indicator condition guided HIV testing strategy in Europe, effectively diagnosing individuals with HIV infection. Phase I of the study has demonstrated proof of concept, showing that such an approach is both feasible and acceptable.
All eight IDs individually fulfilled the criteria of demonstrating an HIV prevalence of >0.1%, with some variation. Despite the recognition that these IDs are related to HIV infection and occur more commonly in those infected, there are little data on previously undiagnosed HIV prevalence among individuals presenting with these conditions. Implementing this strategy across Europe would have significant resource implications. However, data from the US and France propose testing to be cost effective if it is delivered at an HIV positivity rate of 0.1% 
, and the results of HIDES I indicate this cut off is likely to be achieved for each of the eight clinical conditions investigated. However, there may be a degree of variation across Europe in regard to health care utilization and costs, and further country specific data are required to analyse cost effectiveness. Furthermore, in two of the conditions, the target fell within the 95% CI. Increased recruitment through the planned second phase (HIDES II) should be able to further address these issues.
The high HIV prevalence in individuals presenting with a STI is expected, as they share their route of transmission, and the prevalence approaches those rates reported elsewhere (8.8–15.1% among MSM attending UK GUM clinics, for example) 
. However the high detection rate in STI in HIDES I, is also likely to be influenced by the fact that clinics participating in the STI surveys routinely offer HIV tests to all attending individuals regardless of presenting complaint. This is likely to increase both the offer rate and the uptake of testing, as patients expect to be offered a test in this setting, and tests are offered by specialist clinicians in a routine manner.
The HIV prevalence in individuals presenting with a mononucleosis-like illness was also high at 3.85%, and it is possible these symptoms represented HIV sero-conversion. Diagnosis at sero-conversion has the added advantage of enabling an individual to be aware of their HIV status at their most infectious stage, and thus timely diagnosis may potentially impact on levels of onward transmission 
Furthermore, a significant number of patients diagnosed with HIV in the study overall had previously tested HIV negative, and the short median time since their last negative test would suggest early diagnosis had occurred in many of these individuals by utilising this strategy. Additionally, the presenting median CD4 count for all patients diagnosed with HIV in the study is higher than that reported at national levels 
and adds further weight to this strategy being effective in diagnosing HIV infection at an earlier stage.
The differences in the patient characteristics observed are likely to be due, in part, to different surveys being carried out in different regions: 40% of individuals in Northern Europe were included in a STI survey compared to none in East Central Europe; the majority (43%) of individuals recruited in East Central Europe were included in a hepatitis survey. Of individuals in East Central Europe, 29% were included in a MON survey, significantly higher compared to the other regions. This is due to the methodology, whereby each centre only recruited to a proportion of the eight ID (range 1–5), and the IDs were self-selected.
Although the odd ratio of testing HIV positive was higher in those with well-recognised risk-factors (MSM, non-white ethnicity and IDU) individuals presenting with an ID but not from these groups had an HIV prevalence of 0.81%, still far exceeding the 0.1% target. Given that risk-based targeted testing as a strategy to date has not been sufficiently effective, and that in many health care settings information about risk factors is not sought or elicited, indicator condition guided HIV testing is a worthy additional strategy to enhance current testing programmes.
The uptake rates reported suggest the strategy is acceptable to patients regardless of setting or ID, and is higher than that reported elsewhere 
. The offer rate, where available, varies significantly between acute and primary care settings. The offer rate in acute settings is higher than that reported elsewhere 
; in primary care it is lower than some reports 
, however it is similar to some experience outside research studies [unpublished data]. It may be the offer rate is a surrogate marker of the strategy’s acceptability to staff, or it may represent organisational factors within primary care impacting on feasibility. This discrepancy warrants further study.
Staff involved in the study identified major barriers to delivering ID guided testing, including operational, attitudinal barriers, and training needs: however in the majority of settings this was not reflected in light of the high offer and uptake rates. Some of this may be due to study staff incorrectly attributing attitudes to local clinic staff; however the clinic staff themselves did report a high level of predominantly operational barriers, along with perceptions of low risk. This is similar to that reported elsewhere 
and poses a significant challenge to rolling out any strategy calling for increased testing and aiming to ‘normalise’ the offer of an HIV test. It is possible that the introduction of indicator condition guided testing could remove some of the health provider barriers to the offer of a test. Removing the need for risk assessment and making indicator conditions a trigger for the routine offer of an HIV test has the potential to reduce HIV related stigma and discrimination and increase the number of tests offered and accepted, thus ‘normalising’ HIV testing.
shows prevalence data (where available) for the locations in which the surveys were conducted. In the majority of cases (6/8) the prevalence identified through an ID driven strategy exceeds the local prevalence, suggesting the strategy would be an effective and efficient way of identifying HIV infection, thereby helping to reduce the burden of undiagnosed disease. In one ID, hepatitis, the prevalence range includes prevalence figures for IDU and MSM populations - both high prevalence populations themselves. In the remaining two ID, lymphoma and CIN, the local prevalence data is only available for one site, which contributed less than half the HIV tests, which therefore makes comparison less reliable.
The comparator data are derived mainly from national surveillance data. Other investigational testing strategies reveal differing results, depending on whether they are targeted or general screening HIV programmes in high prevalence areas. These latter, general programmes largely produce lower prevalence figures than our ID driven testing. 
It is likely that the findings of this study overall are generalizable across the European region, albeit requiring some local adaptation. Acceptability, for example, is highly likely to be adversely influenced by issues such as stigma, and access to treatment and care. Prevalence in hepatitis will be affected by levels of IDU and access to prevention programmes such as needle exchange. The healthcare setting may also influence final prevalence rates with different severity and/or chronicity of symptoms impacting on the likelihood of underlying HIV infection. However data to date would suggest, even allowing for such regional differences, the resultant prevalence is likely still to remain above 0.1%. Close monitoring and early review after introducing such a strategy would inform the value of its continuation.
Clinics are encouraged to report audits on HIV prevalence for the various IDs and to implement surveys for new ID conditions through the HIDES II study and the HIV in Europe initiative (www.hiveurope.eu
The relatively small number of patients enrolled in HIDES I has resulted in wide CI around the prevalence estimates for some ID. However the main aim of HIDES I was to define the methodology and ascertain the acceptability and feasibility of the strategy of indicator condition guided HIV testing; with further recruitment to HIDES II more precise prevalence data should appear. There was limited information for individuals testing HIV positive regarding CD4 count at diagnosis, disease stage and access to care; this will be an additional outcome in the second phase of the study. Finally, there was very limited data available on those who declined HIV testing or were not offered a test, which may have introduced bias, as those who declined may have done so already knowing their status. Additionally, staff may have introduced bias by targeting testing on the basis of perceived risk, either high or low.
Indicator condition guided HIV testing is an acceptable, feasible and effective strategy to address the on-going HIV epidemic in Europe by reducing the level of undiagnosed HIV infection, and potentially facilitates earlier diagnosis. In line with ECDC (European Centre for Disease Prevention and Control) guidance, this study demonstrates that individuals presenting to any healthcare setting with any of the eight indicator conditions should be strongly recommended to have an HIV test.
The study has also reiterated that potential barriers to routine testing still exist with clinicians, and this requires urgent address through collaboration and information. A strategy is currently being developed in collaboration with ECDC and WHO Europe aimed at guiding the implementation of this novel public health initiative across Europe. The follow up study, HIDES II, will expand this testing strategy by increasing the number of indicator conditions and centres involved.