HIV Datamart

PHOL conducts centralized HIV diagnostic and viral load (VL) testing for Ontario, and maintains databases that contain information on the vast majority of such testing in the province. These databases were integrated to form the HIV Datamart. In the datamart, a person’s diagnostic and VL test records are linked together.* All information in the HIV Datamart is confidential, and only de-identified aggregate data is shared with OHESI partners.

The HIV diagnostic and VL testing databases used to create the datamart are described in further detail below. These data are collected for clinical purposes and completeness is reliant on clinicians and other providers completing the test requisitions and other related forms.

HIV diagnostic database (1985 onwards)

The HIV diagnostic testing database contains records for all individuals who have had an HIV-negative and/or HIV-positive diagnostic test result in Ontario. All HIV diagnostic testing conducted by health care providers in Ontario is done by PHOL. This includes tests conducted in Canada as part of an immigration medical exam. The databases at PHOL include information on test results and the two forms which are completed as part of the testing process (test requisition and LEP form). Tests conducted for purposes of blood/tissue/organ donation and life insurance eligibility are conducted outside of the public health laboratory system and are not included in the databases. Prenatal tests with HIV-negative results are not included in the testing section of this website as they are part of an HIV testing program that is offered to all pregnant individuals as part of their prenatal care. Of note, HIV-positive prenatal tests ARE included for calculation of positivity rates, but the annual number of these tests is relatively low (five to 16 in recent years).

When someone gets an HIV test in Ontario, the health care provider conducting the test fills out an HIV test requisition that collects information on the individual getting tested for HIV, including age, sex and HIV risk factors. With most HIV testing in Ontario, a blood sample is also taken and sent with the form to PHOL. However, with rapid/POC testing, a blood sample is only taken and sent to the laboratory if the test is reactive (i.e. suggestive of an HIV-positive result). This is done in order for the result to be confirmed through additional testing at the laboratory. A blood sample may also be taken and sent to the laboratory if a rapid/POC test is non-reactive but there is reason to believe the person is in the window period. This is done in order for the sample to be tested using an HIV test with a shorter window period.

If laboratory testing confirms an HIV-positive result and the person has no previous HIV-positive test in the laboratory database system, a second form is sent to the health care provider who ordered the test in order to collect information that may have been missed on the HIV test requisition. This second form was implemented in 1999 and is referred to as the LEP form. The LEP form was changed in 2009 to collect information on race/ethnicity and country of birth, both of were only collected on the HIV test requisition since 2018. Data from the requisition and LEP forms are combined and used for describing trends in new HIV diagnoses (i.e. HIV-positive tests) in Ontario. However, only data from the test requisition are used in the HIV testing section of this website, as LEP data is not available for HIV-negative tests.

In Ontario, individuals testing for HIV may use either their full name (nominal) or a code assigned in specific primary care settings (coded), or test without a code or name at designated HIV testing clinics (anonymous). Coded and anonymous testing are both forms of non-nominal testing.

New HIV diagnosis definition

Only individuals with a confirmed HIV-positive test result and no previous HIV-positive test in the database system are considered to be a new HIV diagnosis. Exclusion of those with a previous diagnosis occurs when that individual’s previous positive result is identified by PHOL. Most excluded individuals are those who have had two or more HIV-positive tests conducted nominally or using the same code within Ontario, since these tests include identifying information that can be used to link tests.

It is not possible to exclude all individuals with a previous HIV-positive result from the new diagnoses numbers. Many individuals who test HIV-positive through coded or anonymous testing also test HIV-positive a second time through nominal testing (e.g. confirming an HIV-positive test is standard practice for some healthcare providers when an HIV-positive person first presents to care). Since these two tests cannot be linked together, both are reported as a new diagnosis – leading to double-counting of these individuals. This means that the reported number of new HIV diagnoses each year is likely higher than the true number of diagnoses. This also means that trends in diagnoses may be influenced by the number of people testing HIV-positive through anonymous and coded testing.

Of note, individuals diagnosed with HIV for the first time outside of Ontario, but who subsequently moved to the province and tested again, are included as a new diagnosis. This means that changes in migration can potentially influence trends in new diagnoses in Ontario.

HIV viral load database (1996 onwards)

VL testing was implemented in 1996 and the database at PHOL contains records for all individuals who have had a VL test in Ontario. In addition to VL test results, the database contains information from the VL test requisition form (completed by the provider), including most recent CD4 count and whether the patient was on ART at the time of testing. Providers complete the information on ART on approximately 80% of VL test requisition forms. As of the end of 2015, all VL tests in the database were conducted nominally.

* It is not possible to link non-nominal HIV-positive diagnostic tests (coded, anonymous) to VL tests in the datamart, as no identifying information is available to facilitate linkage.