Why look at patterns in HIV testing?
- HIV testing is an early step in the HIV prevention, engagement and care cascade (Figure i) and is a critical step for people living with HIV to know their status and be linked to care. HIV testing is also an important gateway to services for people who are HIV-negative. This step is closely tied to the first UNAIDS 90-90-90 target (see box below).
- Trends in HIV testing can be useful for measuring the success of HIV testing initiatives and for interpreting trends in new HIV diagnoses.
- HIV test positivity rates can provide insight into which sub-populations have a higher level of HIV risk. However, HIV positivity rates should be interpreted with caution as they are influenced by both HIV risk as well as those being diagnosed for the first time in Ontario after previously being diagnosed elsewhere (known to be HIV-positive at the time of testing).
- This report includes information on the number of HIV tests in Ontario. It does NOT include information on the number of unique individuals tested. This means trends may reflect changes in both the number of times an individual is tested in a year as well as the total number of unique people who are tested.
Where do these data come from?
- Data in this report come from the Public Health Ontario Laboratory (PHOL), which conducts centralized HIV diagnostic testing for the province.
- When someone is tested for HIV in Ontario, the health care provider conducting the test (e.g. a physician, nurse or HIV counselor) fills out an HIV test requisition form that is sent to PHOL. The requisition collects information on the individual being tested for HIV, including their age, sex, geographic location and HIV risk factors.
- When a test is HIV-positive, a Laboratory Enhancement Program (LEP) form is sent to the health care provider who conducted the test to collect more information on the individual tested. However, only data from the test requisition are used in this report, as LEP data is not available for HIV-negative tests.
- With rapid/point-of-care (POC) tests, an HIV test requisition form is completed and submitted to PHOL with a sticker attached indicating the result of the POC test. POC tests are included in the total numbers of tests in this report, and reactive POC tests with confirmatory laboratory tests are included as positive HIV tests in the positivity rates.
- Prenatal HIV tests are part of an HIV testing program offered to all pregnant individuals as part of their prenatal care. Prenatal HIV testing results are presented separately here and are not included in the number of HIV tests or population testing rates in this report. However, to calculate HIV positivity rates, HIV-positive prenatal tests are included in the numerator while HIV-negative prenatal tests are not included in the denominator. From 2013 to 2017, the annual number of HIV-positive prenatal tests ranged from four to 15.
- More information on the source of these data can be found here.
What are some of the strengths of these data and our approach to presenting it?
- All HIV diagnostic testing conducted by health care providers in Ontario is done by PHOL and therefore included in this report.
- Age, sex and geography data on the test requisition are very complete and available for more than 96% of HIV tests since 2008.
- Trends in HIV tests are presented as numbers and, where possible, as an HIV testing rate (i.e. the number of tests per 1,000 people). While the number of tests is influenced by the size of the underlying population (i.e. greater population = greater number of tests), rates take population size into account and remove it as a possible explanatory factor for any observed differences over time or between populations.
What are some of the limitations of these data?
- For this report, information about new HIV diagnoses is limited to what can be obtained from the HIV test requisition form alone (and not the LEP); therefore, not all information about duplicate diagnoses (including those being diagnosed for the first time in Ontario after being diagnosed previously elsewhere) is reflected in the HIV positivity rates.
- Before 2018, the HIV test requisition did not collect information on race/ethnicity, country of birth and transgender identity. Lack of race/ethnicity and country of birth information means it was not possible to look at HIV testing by priority population in this report. In early 2018, PHOL implemented a revised HIV test requisition that collects these data.
- In this report, HIV tests are broken down by exposure categories, which are meant to represent an individual’s most likely risk of HIV infection based on risk factors documented on the HIV test requisition. The HIV response in Ontario focuses on priority populations or populations most effected by HIV, which are a combination of risk factors (e.g. men having sex with men, injection drug use) and race/ethnicity (e.g. from countries where HIV is endemic). As information on race/ethnicity was not available on test requisition forms up to and including 2017, we are unable to report on priority populations here. Exposure categories do not capture the burden of HIV in communities. In particular, the classification of endemic exposures is inadequate to address HIV in African, Caribbean and Black communities. More information on Exposure categories can be found in the technical notes.
- For over half of test requisition forms risk factor information is missing or indicated as “none”. Because an exposure category could not be assigned for these tests, they were excluded from the exposure category section of this report. Due to the extent of missing information, exposure category data are presented as the proportion of HIV tests where exposure category was known. The total number of tests by exposure category is not presented as they are underestimates.
- If information is more likely to be missing for one specific exposure category than others (e.g. injection drug use), that exposure category may be underrepresented in the data and could introduce bias into the findings of this report.
- Tests are reported as a rate per 1,000 people. It is possible that an individual may test more than once per year and, therefore, the number of unique individuals tested may be lower than the total number of tests.
- All HIV tests that were not linked to a previous positive result at the public health lab are included here. This includes any retest in Ontario that cannot be linked and any first time positive in Ontario. This means that some proportion of tests were carried out on people who were already aware of their status. See “New HIV Diagnoses in Ontario, 2017” report for more detail.