In this issue of the journal, Supervie et al., using a back-calculation approach, estimated the number of undiagnosed HIV-infected individuals in France. To respond to the HIV threat, one key step is to provide updated estimates of the number of persons living with HIV, thereby better understanding the burden of the disease, assessing healthcare needs, and designing public health interventions. An accurate estimate of the prevalence of undiagnosed HIV infection, along with knowledge of characteristics of this population, is particularly important for designing appropriate and effective HIV prevention and testing strategies.
Supervie et al. estimated that in 2010 in France, 29 000 (95% confidence interval: 24 200–33 900) out of 83 800 individuals newly infected with HIV between 2000 and 2010 had been living with undiagnosed HIV infection. Using different methodological approaches, in the United Kingdom and the Netherlands, the proportion of undiagnosed HIV persons was estimated at 24 and 40%, respectively [2,3]. The number of undiagnosed HIV infection when compared with overall HIV-infected patients is not negligible in western Europe, attesting to the fact that HIV testing efforts remain a public priority in this region.
Persons living with undiagnosed HIV infection, as illustrated by Supervie et al., do not have timely access to treatment: 59.6% had a CD4+ cell count less than 500/μl and were eligible for antiretroviral treatment based on French guidelines. They are, therefore, at higher risk of morbidity and mortality . In addition, undiagnosed persons constitute the principal fraction of the community viral load reservoir, driving HIV transmission and contributing to sustaining the epidemic. In the United States, it has been estimated that almost 50% of new HIV infections arose from those who had been undiagnosed . In France, undiagnosed HIV-infected persons may be responsible for 43–60% of transmissions . Their impact upon transmission is growing with time given that important efforts are currently focusing on providing therapy earlier in the course of the disease in diagnosed patients (i.e. the concept of treatment as prevention, TasP ).
The findings of Supervie et al. suggest that about two-thirds of those with undiagnosed HIV infection are either MSM or non-French heterosexuals. Thus, testing strategies should target these populations (i.e. a risk-factor-based testing strategy). However, studies have demonstrated the weak efficiency of risk-factor-based HIV testing. Individuals may not consider themselves at risk and healthcare providers may fail at risk assessment. In a recent study in France, among MSM who had had a medical encounter during the 3-year period prior to HIV diagnosis, only 48% had informed the healthcare provider that they belonged to a risk group . In France, as in the United Kingdom, the incidence of HIV among MSM remains high and stable, and has even increased [9–11].
Since 2006, recognizing the need to reconsider the approach to HIV testing, the Center for Disease Control recommends routine screening in the United States . Since 2012, based on new evidence of the clinical and public health benefits of early identification of HIV, the US Preventive Services Task Force (USPSTF) has assigned a grade A recommendation for screening for HIV in the general population, with important policy implications (i.e., public and private health plans provide coverage for USPSTF-recommended preventive services without patient copayments). Mainly because of the lower prevalence of HIV and the higher numbers of nonroutine HIV tests performed, routine HIV testing strategies have not been used in Europe. However, the proportion of undiagnosed HIV persons in many western European countries is no less than that in the United States [2,13,14]. Moreover, the specific impact of undiagnosed patients upon HIV transmission is probably even higher in European countries such as UK and France where, because of a better linkage and adherence to care, diagnosed patients more frequently have undetectable viral loads and are consequently less infectious than in the United States [2,13,14]. Finally, previous studies illustrated that routine HIV testing in a general population in these settings is cost-effective . In 2009, new French guidelines recommended one-time routine voluntary HIV screening strategy for people without a past history of HIV testing. However, those recommendations have not been applied because of their budget impact and problems of feasibility . General practitioners, the point-of-entry into the healthcare system, do not adhere to routine HIV testing, considering a very small number of patients will test positive.
Supervie et al. demonstrate that 70% of patients with undiagnosed HIV infection are men. As most women are tested for HIV at least once during pregnancy, a more efficient and cost-effective strategy might involve one-time routine HIV testing for men. This nonrisk-factor-based strategy will detect MSM, the core of the HIV epidemic. In addition, it will have a lower budget impact and, as a result, will be easier to implement. However, in order for this strategy to be applicable, it is important to reconsider, at the public health and population level, the role of healthcare providers such as general practitioners, who are currently primarily focused on individual care.
In addition to testing initiated by the healthcare provider, we must implement other screening strategies to increase the number and the frequency of HIV testing, in particular among persons at highest risk of new infection. Community HIV testing in nonclinical settings represents one opportunity for diagnosing HIV infection among individuals who may not have contact with health services, especially in hard-to-reach groups such as migrants, and for testing more frequently MSM . Although the optimal self-testing paradigm has yet to be established , rapid self-testing offers another unique opportunity for improving HIV testing [19,20].
In a recent editorial, Walensky and Bassett  stated that ‘Whatever the next hottest, scientifically proven HIV treatment or prevention strategies are, they will share a common denominator for implementation: the HIV test’. One of the major priorities in the future will be to design and implement the most effective and cost-effective HIV testing strategies. The study by Supervie et al. gives us insight into characteristics of the hidden epidemic and is of great importance for implementing efficient HIV testing strategies.
Conflicts of interest
Y.Y. has received travel grants, lecture fees and consulting honoraria from Abbott/Abbvie, Bristol-Myers Squibb Gilead, Roche, Schering-Plough/Merck, Tibotec and ViiV Healthcare.
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