Background We described the impact of different lengths of lookback window (LW), a retrospective time period to observe diagnoses in administrative data, on the prevalence and incidence of eight chronic diseases. Methods Our study populations included people living with HIV (N = 5151) and 1:5 age-sex-matched HIV-negative individuals (N = 25,755) in British Columbia, Canada, with complete follow-up between 1996 and 2012. We measured period prevalence and incidence of diseases in 2012 using LWs ranging from 1 to 16 years. Cases were deemed prevalent if identified in 2012 or within a defined LW, and incident if newly identified in 2012 with no previous cases detected within a defined LW. Chronic disease cases were ascertained using published case-finding algorithms applied to population-based provincial administrative health datasets. Results Overall, using cases identified by the full 16-year LW as the reference, LWs ≥8 years and ≥ 4 years reduced the proportion of misclassified prevalent and incidence cases of most diseases to < 20%, respectively. The impact of LWs varied across diseases and populations. Conclusions This study underscored the importance of carefully choosing LWs and demonstrated data-driven approaches that may inform these choices. To improve comparability of prevalence and incidence estimates across different settings, we recommend transparent reporting of the rationale and limitations of chosen LWs.

T he personal and public health benefits of early initiation of antiretroviral treatment (ART) are well documented. [1][2][3][4][5] In addition to decreasing morbidity and mortality rates among people living with HIV/ AIDS, 1-3 ART has also been shown to reduce the incidence of HIV cases in a population. 4,5 This evidence led to the conception of HIV treatment as prevention (TasP), the scaling-up of testing followed by the immediate initiation of ART, as a strategy for reducing AIDS-related morbidity and death, as well as the spread of HIV. [6][7][8] The success of TasP for HIV transmission relies on the ART-led suppression of HIV replication, resulting in sustained undetectable viral load in bodily fluids and a risk of sexual transmission of HIV that is effectively zero -referred to as "undetectable = untransmissible" (U=U). 9,10 To achieve the goal of ending AIDS as a pandemic by 2030, the United Nations Joint AIDS Programs (UNAIDS) proposed the TasP-based 90-90-90 target, whereby at least 90% of people living with HIV have a diagnosis, 90% of people with an HIV diagnosis are treated with ART and 90% of ART-treated people living with HIV are virologically suppressed by 2020. 11 Meeting the 90-90-90 target would result in a substantial decrease in AIDS-related morbidity and mortality rates and new HIV infections within a decade. 12,13 The global progress toward the 90-90-90 target has been encouraging, despite political, fiscal and programmatic challenges. [14][15][16][17][18]

No abstract