Towards standardised definitions for monitoring the continuum of HIV care in Europe.

The continuum of HIV care is a simple conceptual framework for monitoring HIV programmes, comprising a series of stages that people living with HIV (PLHIV) pass through to access antiretroviral treatment (ART) and achieve viral suppression [1,2]. Individual benefits of suppression include reduced risk of morbidity and mortality. At the population level, viral suppression reduces the risk of onward transmission and enables epidemic containment [3]. Transmission risk may be further reduced by lowering the number of undiagnosed PLHIV [4,5]. Complete continua are, therefore, constructed beginning with the total number of PLHIV in a given population and ending with the number virally suppressed. Intervening stages have included the numbers diagnosed, linked to HIV care, retained in care, eligible for ART, on ART and adhering to ART. Although people can move between stages, the continuum is typically conceptualized as a ‘snapshot’ at one time-point. As the Joint United Nations Programme on HIV and AIDS (UNAIDS) announced the target of reaching ‘90-90-90’ by 2020, which envisions 90% of PLHIV diagnosed, 90% of those diagnosed on ART and 90% of those on ART virally suppressed [6], interest in constructing HIV care continua to inform national programmes and policies has grown [7–11]. However, there has been limited consistency in the methods used to construct these measures and the stages presented in publications. Key stages are often missing or continua entirely absent for many countries, including in Europe, particularly the Eastern region [7,8,11–15]. Drawing from a review of recent literature and expert opinion, we highlight the methodological inconsistencies, the challenges associated with constructing each stage and recommend a standardized way forward for monitoring the continuum of HIV care in Europe.