Table 1. Operational definitions for the six stages of the cascade of HIV care in Estonia, 2013.

Stage	Operational definition, data with respective time period	Data source(s)
Living with HIV	The Spectrum estimate for 2013	UNAIDS
Diagnosed with HIV (alive in 2013)	Aggregated number of confirmed HIV-positive tests (individuals) minus the aggregated number of deaths (AIDS deaths, specified proportion of deaths related to illicit drug overdose) Time period: 1 January 1988a– 31 August 2013b	EHB; ECDR
Linked to HIV care (alive in 2013)	The number of individuals with at least one HIV-related healthcare visit, based on individual anonymised reimbursement claims of HIV-related healthcare services: visit dates, medical services provided to PLHIV (with dates), healthcare providers issuing the claims Time period: 3 February 2000c–31 August 2013b	EHIF
Retained in HIV care	The number of individuals with two or more HIV-related healthcare visits (at least three months apart) within the past 12 months Time period: 1 September 2012–31 August 2013d	EHIF
On ART	Step 1: The proportion of individuals on ART among those retained in care, based on individual anonymised data from E-HIV: HIV confirmation date, ART initiation date, dates and results of CD4+ T-cell and HIV RNA tests, dates of other provided medical services Step 2: The number of individuals on ART among those retained in care according to EHIF, when applying the proportion obtained in Step 1 to individuals retained in care according to EHIF Time period: 1 September 2012–31 August 2013d	E-HIV; EHIF
Virally suppressed	Step 1: The proportion of individuals on ART with the most recent (within the past 12 months) HIV RNA level < 200 copies/mL, based on individual anonymised data from E-HIV Step 2: The number of individuals virally suppressed according to EHIF, when applying the proportion obtained in Step 1 to individuals on ART according to EHIF Time period: 1 September 2012–31 August 2013d	E-HIV; EHIF

AIDS: acquired immunodeficiency syndrome; ART: antiretroviral therapy; ECDR: Estonian Causes of Death Registry; EHB: Estonian Health Board; EHIF: Estonian Health Insurance Fund; E-HIV: Estonian HIV Cohort Study; HIV: human immunodeficiency virus; PLHIV: people living with HIV; UNAIDS: Joint United Nations Programme on HIV/AIDS.

^a The first HIV case in Estonia was diagnosed in 1988.

^b End of our study period.

^c Earliest date appearing on an HIV-related medical service reimbursement claim (the date of opening the medical service account) in the EHIF electronic database since its inception.

^d To evaluate the situation in 2013, data from this 12-month period were used.