Where do these data come from?
- Data in this section comes from the Public Health Ontario Laboratory (PHOL), which conducts centralized HIV diagnostic and viral load (VL) testing for the province.
- PHOL’s HIV diagnostic and VL databases were combined and used to create a group (also known as a cohort) of people living with diagnosed HIV in Ontario – referred to as the Ontario HIV Laboratory Cohort – whose cascade engagement can be monitored over time. The cohort includes all people in the laboratory databases who have record of a nominal HIV-positive diagnostic test and/or at least one VL test, and have not been administratively lost-to-follow-up (LTFU). For more information on who is and isn’t included in this cohort, go here.
- All information in the PHOL databases is confidential, and only de-identified aggregate data are shared with OHESI partners.
What are some of the limitations of these data?
- An important limitation is the inability to determine who in the cohort has died or migrated out of the province when estimating the number of people with diagnosed HIV living in Ontario. If a diagnosed individual in the cohort does not have a VL test in a given year, it is not possible to determine the reason (e.g. migration out of the province, death or actual disengagement from care) from the laboratory data. To account for possible migration or death, individuals were removed from the cohort (administratively LTFU) if they had no record of a VL test for more than two consecutive years. However, it is possible that some of these individuals were still living in the province (but not connected to care), and therefore the number of individuals in the cohort may be lower than the actual number living with diagnosed HIV in the province. If a person administratively LTFU subsequently re-engages in care, they are re-entered into the cohort and counted as being a diagnosed person living with HIV in the province in all years since their last VL test.
- The exclusion of non-nominal HIV-positive diagnoses from the cohort may mean the number of people with diagnosed HIV is underestimated. However, many people diagnosed non-nominally end up receiving either a nominal HIV-positive diagnostic test or a nominal VL test when they enter care and would therefore be included in the cohort.
- We included non-nominal HIV-positive diagnoses and extended the administrative LTFU criteria to three years to create an “Upper” estimate of the number diagnosed.