The undiagnosed HIV epidemic in France and its implications for HIV screening strategies.

BACKGROUND: Describing the undiagnosed HIV-infected population is essential for guiding HIV screening policy, implementing interventions, and resource planning. METHODS: We used French national HIV surveillance data and a back-calculation approach to estimate the number of undiagnosed HIV-infected individuals in France and the distribution of time since HIV infection among undiagnosed individuals. We also used data on CD4⁺ cell count decline to assess the CD4⁺ cell count distribution among undiagnosed individuals. RESULTS: We estimated that 29,000 [95% confidence interval (CI): 24,200-33,900] individuals were living with undiagnosed HIV infection at the end of 2010. Of these, 28.7% (95% CI: 27.1-30.4) were infected less than a year ago, 16.4% (95% CI: 15.0-17.8) more than 5 years ago, and 59.6% (95% CI: 59.2-59.8) were eligible for antiretroviral treatment (CD4⁺ cell count less than 500 cells/µl) according to the 2010 French guidelines. Men represented 70.0% of the undiagnosed HIV-infected individuals and had lower CD4⁺ cell counts than women. The numbers of undiagnosed infections in MSM, non-French national heterosexuals, and French national heterosexuals were similar (9200, 9300, 10,000, respectively). However, because of differences in group size, undiagnosed HIV prevalence varied significantly between these groups (2.95, 0.36, 0.03%, respectively; P less than 0.001). CONCLUSION: Our findings suggest that many undiagnosed HIV-infected individuals were eligible for treatment and, thus, lack of HIV diagnosis is a lost chance for them; many more heterosexuals than MSM will need to be tested to find those undiagnosed; and universal screening of men may be cost-effective, especially in the areas most affected by the epidemic, such as the Paris region.