Identifying population-specific HIV diagnosis gaps in Western Africa and assessing their impact on new infections: a modelling analysis for Côte d'Ivoire, Mali and Senegal

International audienceBACKGROUND: Progress towards HIV elimination in Western Africa may be hindered by diagnosis gaps among people living with HIV (PLHIV), especially among key populations (KP) such as female sex workers (FSW), their clients, and men who have sex with men (MSM). We aimed to identify largest gaps in diagnosis by risk group in Mali, Côte d'Ivoire, and Senegal, and project their contribution to new HIV infections.METHODS: Deterministic models of HIV transmission/diagnosis/treatment that incorporate HIV transmission among KP were parameterized following comprehensive country-specific reviews of demographic, behavioural, HIV and intervention data. The model was calibrated to country- and group-specific empirical outcomes such as HIV incidence/prevalence, the fractions of PLHIV ever tested, diagnosed, and on treatment. We estimated the distribution of undiagnosed PLHIV by risk group in 2020 and the population-attributable-fractions (tPAFs) (i.e. fraction of new primary and secondary HIV infections 2020-2029 originating from risk groups of undiagnosed PLHIV).RESULTS: From 46% (95% UI: 38-58) to 69% (59-79) of undiagnosed PLHIV in 2020 were males, with the lowest proportion in Mali and the highest proportion in Senegal, where 41% (28-59) of undiagnosed PLHIV were MSM. Undiagnosed men are estimated to contribute most new HIV infections occurring over 2020-2029 (Table). Undiagnosed FSW and their clients contribute substantial proportions of new HIV infections in Mali, with tPAF=20% (10-36) and tPAF=43% (26-56), respectively, while undiagnosed MSM in Senegal are estimated to contribute half of new infections. A lower proportion of new HIV infections are transmitted by undiagnosed KP in Côte d'Ivoire (tPAF=21%(10-38)).CONCLUSIONS: Current HIV testing services and approaches are leaving members of KP behind. Increasing the availability of confidential HIV testing modalities in addition to traditional tests may substantially reduce gaps in HIV diagnosis and accelerate the decrease of new HIV infections in Western Africa since half of them could be transmitted by undiagnosed KP