Refining HIV surveillance on new HIV diagnoses in Ontario


  • In Ontario, the number of new HIV diagnoses has increased in recent years. Challenges to interpreting diagnosis trends include:
    • The double-counting of individuals diagnosed through anonymous testing (duplicate diagnoses).
    • The inclusion of people who were diagnosed outside of the province and later moved to Ontario and tested again (‘out-of-province’ diagnoses).
  • In recent analyses led by OHESI, removing duplicates decreased the number of diagnoses in 2017 from 935 to 916. Also removing ‘out-of-province’ diagnoses further reduced this number to 797.
  • These analyses also suggest that the overall increase in new diagnoses between 2016 and 2017 was the result of an increase in ‘out-of-province’ diagnoses, rather than an increase in new HIV transmissions in the province.

Surveillance data on new HIV diagnoses are often used by front-line service providers and policy makers to inform their work. Information collected on diagnoses, such as sociodemographics and HIV risk factors, is commonly used to:

  • guide the planning and delivery of appropriate HIV care.
  • inform HIV prevention initiatives and evaluate their success (as new diagnoses are often used as an indirect way of measuring new infections).

This blog post describes the challenges of using Ontario surveillance data for the above purposes, OHESI’s recent work in refining these data and the impact of these refinements on recent trends.

Information collected during HIV testing in Ontario

Before discussing refinements to HIV surveillance, it is important to understand the HIV testing process and how information on newly diagnosed individuals is collected in Ontario.

When a person is tested for HIV in the province, the health care provider ordering the test fills out an HIV test requisition form. This form collects information on the person tested, including sex, date/year of birth, HIV risk factors and either the person’s name (nominal testing) or an anonymous code (anonymous testing).

When a person tests positive for HIV, Public Health Ontario sends a second form – the Laboratory Enhancement Program (LEP) questionnaire – to the health care provider who ordered the initial test. The purpose of this second form is to supplement the HIV test requisition and provide a more comprehensive understanding of who is being diagnosed with HIV in Ontario. Data collected on the LEP form includes some of the same information documented on the requisition form, as well as other information, such as race/ethnicity, country of birth and HIV testing history.[1]

Double-counting of diagnoses

In Ontario, a new diagnosis is defined as an individual’s first HIV-positive test result in the province. This means that if a person receives more than one HIV-positive test in Ontario (see Box below), only the first test is counted as a new diagnosis in order to avoid double-counting. Duplicate diagnoses are identified and removed when test information is entered into the laboratory surveillance databases at Public Health Ontario.

Why might a second HIV diagnostic test be conducted?

There are several possible reasons. For example, some physicians order an HIV test to confirm an individual’s diagnosis when the person first enters care.

Anonymous testing provides an important option for people concerned about privacy; however, it complicates the accurate collection of surveillance information and can result in an individual being counted twice in the data. With anonymous testing, duplicate diagnoses are difficult to identify due to the lack of identifying information collected on the person tested. For example, someone who initially received an HIV-positive diagnosis through anonymous testing, and later had a nominal HIV test when entering care, may be counted twice as a new diagnosis.[2] Individuals who receive more than one anonymous HIV-positive test may also be counted twice.

When people are double-counted, the number of new diagnoses included in Ontario surveillance reports is higher than the actual number of diagnoses.

‘Out-of-province’ diagnoses

Interpretation of diagnosis trends is also complicated by individuals who were initially diagnosed outside of Ontario and then moved to the province and tested for HIV again (for example, as part of the immigration process or when entering care). These ‘out-of-province’ diagnoses are counted as a new diagnosis in Ontario and their inclusion means that trends can be influenced by migration patterns to the province, in addition to other factors. This makes it difficult to interpret trends. For example, an increase in new diagnoses could be due to more HIV transmissions occurring in Ontario, more HIV-diagnosed individuals moving to and being re-tested in Ontario, or a combination of both.

Refining Ontario’s HIV surveillance data

OHESI (a collaboration between Public Health Ontario and the Ontario HIV Treatment Network, AIDS Bureau of the Ontario Ministry of Health and Long-Term Care, and Public Health Agency of Canada) is dedicated to providing the best possible provincial surveillance numbers for Ontario. By refining the new diagnosis data, we may be able to better estimate the actual number of people who receive a first time HIV-positive diagnosis in Ontario, as well as improve our ability to interpret trends.

Recently, OHESI conducted new analyses to determine how information collected on HIV testing history (on the LEP form) could help improve these data. This LEP-based information includes when and where an individual has previously tested positive for HIV.[3]

In these new analyses:

  • diagnoses with history of a previous HIV-positive test result within Ontario were removed in order to reduce double-counting (as these diagnoses are duplicates and would have already been counted as a new diagnosis with their first positive test in Ontario).
  • individuals with history of a previous HIV-positive test result outside of Ontario (‘out-of-province diagnoses) were removed in order to better assess trends in new HIV infections that occurred in the province (as these individuals were most likely infected with HIV outside of Ontario).

Note: Diagnoses with history of a previous HIV-positive test result are referred to as ‘previous positives’ in the remainder of this post.

What is the impact of removing previous positives?

Trends in the number of new diagnoses in Ontario between 2008 and 2017 are shown in the figure below, along with the impact of excluding previous positives.


Line graph showing new diagnoses with previous positives removed (over time)

The top line displays the trend in new diagnoses when the LEP is not used to remove any previous positives. This line shows a decrease in diagnoses in the earlier part of the past decade, followed by an increase between 2013 and 2017.

When the LEP form is used to address double-counting and remove duplicate diagnoses with history of a previous positive test result within Ontario (the middle line), the trend is identical but there are an average of 22 fewer diagnoses each year.

When ‘out-of-province’ diagnoses are also removed (the bottom line), the difference is more noticeable. In this scenario, the trend is identical until 2016 and then – instead of continuing to increase – the number of new diagnoses in Ontario decreases to 797 in 2017.

Taken together, these data suggest that the increase in new diagnoses between 2016 and 2017 (as observed in the top and middle lines) was the result of an increase in ‘out-of-province’ diagnoses, rather than an increase in new HIV transmissions in the province. Further, these data suggest that the number of new HIV infections occurring in Ontario in recent years may be closer to 800 than 900, and possibly lower (information on HIV testing history is missing for about half of diagnoses each year).[4]


Moving forward, OHESI will use information collected on HIV testing history to refine Ontario diagnosis data.

Future OHESI knowledge exchange products will exclude diagnoses with history of a previous positive within Ontario to reduce double-counting. Importantly, OHESI will continue to include ‘out-of-province’ diagnoses to provide an accurate picture of how many people and who require HIV care in the province. However, in separate tables and figures, OHESI will also exclude ‘out-of-province’ diagnoses in order to better understand trends in new HIV infections and guide HIV prevention priorities.

We hope these refinements will enhance the usefulness of surveillance data for people working in HIV.


  1. Race/ethnicity, country of birth and HIV testing history were added to the HIV test requisition in 2018.
  2. In Ontario, an average of 115 people are diagnosed with HIV through anonymous testing each year. However, it is unclear how many of these individuals also receive an additional anonymous and/or nominal HIV-positive diagnostic test and are double-counted.
  3. Information on HIV testing history has been collected on the LEP since the questionnaire was introduced in 1999, but is not available for every diagnosis. Approximately 50% of new HIV diagnoses have both 1) an LEP questionnaire returned, and 2) the HIV testing history section of the questionnaire completed.
  4. Additional caution is needed when using new HIV diagnoses as an indirect measure for new HIV infections. This is because many people are not diagnosed in the year they become infected with HIV. OHESI is currently working with mathematical modelers to better estimate the number of new HIV infections.

OHESI releases new report on HIV testing trends in Ontario

OHESI is pleased to announce the release of a new report titled “HIV testing in Ontario, 2016”.

Download report

HIV testing is an early step in the HIV prevention, engagement and care cascade and an important gateway to a continuum of services. A person who receives an HIV-negative test result can be linked to supports to remain HIV-uninfected, while those receiving an HIV-positive result can be promptly linked to care and treatment. As we have learned more about HIV prevention strategies for HIV-negative individuals (for example, pre-exposure prophylaxis and services to address syndemic health issues), and the role of earlier treatment of people living with HIV in improving health and reducing HIV transmission, the importance of HIV testing has only increased.

The Ontario HIV/AIDS Strategy prioritizes the reduction of barriers to HIV testing in order to achieve its goals of preventing new HIV infections and promoting early HIV diagnosis. Over the past decade, several initiatives have been implemented in Ontario to achieve these goals, such as the expansion of anonymous testing sites in 2006, an HIV testing blitz program aimed at gay and other men who have sex with men in Toronto and Ottawa in 2011-2012 and the release of HIV testing frequency guidelines in 2012. In this time, new testing technologies have also been developed and made available in Ontario, including point-of-care tests that can provide results within minutes and HIV tests with shorter window periods.

The newly released OHESI report being announced today supports the strategy in monitoring trends in HIV testing. This new report contains data on the number of HIV tests from 2007 to 2016 and breaks this information down by age, sex, test type (i.e. nominal, anonymous, coded), exposure category and geography. This report also contains information on the percent of HIV tests that were HIV-positive (i.e. positivity rates). Testing trends are not only important for evaluating the success of testing initiatives and identifying populations for prioritization, but also provide insight into trends in new HIV diagnoses (published in a separate OHESI report).

We hope this report is useful for evaluating and guiding HIV policy and programming work across the province.

OHESI releases new report on cascade trends by sex, age and health region

OHESI is pleased to announce the release of a new report titled “HIV care cascade in Ontario by sex, age and health region: Linkage to care, in care, on antiretroviral treatment and virally suppressed”.

Download report

In recent years, the HIV care cascade has become a core framework for those working in HIV. In its simplest form, the cascade refers to the continuum of steps that people living with HIV progress through in order to achieve viral suppression, including testing and diagnosis, linkage to and retention in care, and initiation of and adherence to antiretroviral treatment. As more research has shown the importance of viral suppression for both improving health and eliminating the risk of HIV transmission to a sex partner, the cascade has become an essential framework for evaluating and identifying gaps in HIV care.

With the release of the Ontario HIV/AIDS Strategy in 2016, Ontario joined other jurisdictions around the world in re-orienting HIV policies and programming to focus on the HIV cascade. In support of the priorities set out in the strategy, OHESI published a report summarizing trends in HIV cascade engagement among the approximately 16,000 people with diagnosed HIV living in Ontario. Importantly, this report was the first to draw upon a new data source that was created using centralized diagnostic and viral load testing databases housed at Public Health Ontario. The analyses in the report demonstrated improvement in the proportion of people with diagnosed HIV who were in care, on antiretroviral treatment and virally suppressed over time. Missing from the report, however, were cascade estimates by demographics and other breakdowns important for informing policy and front-line programming.

The newly released OHESI product being announced today builds upon this previous report by presenting cascade estimates by sex, age and health region in Ontario. The good news is that estimates have generally improved over time for both sexes, as well as across age categories and health regions. However, the report also demonstrates lower cascade estimates for people of younger ages and those living in the Northern health region, and slightly lower estimates for females and those living in Ottawa. These results support the need to understand reasons for variations in cascade engagement, which could lead to prioritizing interventions for specific populations.

Stayed tuned for an OHESI factsheet based on the findings from this report, as well as another knowledge exchange product presenting cascade estimates by priority populations, where possible. These populations are outlined in Ontario HIV/AIDS strategy and include gay, bisexual and other men who have sex with men, including trans men; African, Caribbean and Black people; Indigenous people; people who use drugs; and women at-risk, including trans women.

OHESI Launches New Website for World AIDS Day 2017

World AIDS Day provides an opportunity to remember those who lost their lives to HIV/AIDS, to educate people about the impacts and prevention of HIV infection, to celebrate our accomplishments, and to support those in the continued fight against the pandemic. Today we announce the release of a new OHESI website to commemorate World AIDS Day.

In Canada alone, more than 18,000 people have died as a result of HIV infection since 1987. Our most recent estimates for Ontario suggest that over 16,000 people diagnosed with HIV are living in the province. Recent data show that there have been vast improvements in the health and life expectancy of people living with HIV. Data for Ontario’s HIV care cascade show that an increasing percentage of people are taking antiretroviral medications and living with a suppressed viral load.

However, ongoing new HIV infections and the need to support the health of individuals living with the virus require continued dedication to the monitoring and surveillance of the epidemic in Ontario. The best possible data is needed to support strategies, programs, and partnerships to improve HIV treatment and prevention.  The launch of the new OHESI website and provision of the most current available data about Ontario’s HIV epidemic will further our collective efforts to develop evidence-based policy and programming. As a collaboration of several lead HIV organizations (the AIDS Bureau at the Ministry of Health and Long Term Care, Public Health Ontario, and the Public Health Agency of Canada, and the Ontario HIV Treatment Network), OHESI strives to support the vision of the HIV/AIDS Strategy to 2026 where new infections will be rare in Ontario and people with HIV will lead long, healthy lives free from stigma and discrimination.

World AIDS Day brings us together to remember those who have passed on, to share knowledge, and to support the response to HIV/AIDS. We support this event with reinvigorated optimism and a strategy for the future.

Please join the OHESI mailing list to have access to the most up to date information on HIV/AIDS in Ontario.

Preliminary update on new HIV diagnoses in Ontario

The Ontario HIV Epidemiology and Surveillance Initiative (OHESI) is pleased to announce the release of a preliminary update on new HIV diagnoses in Ontario.

View report

In this update you will find the number, rates, and breakdowns of new HIV diagnoses for 2016 and trends over time. This update is intended to provide information to support public health professionals, clinicians, health system planners, policy makers and the leadership of AIDS service organizations, as well as other engaged stakeholders. The update is based on HIV diagnostic test results from public health laboratory systems.

A full report on HIV diagnosis and testing is currently being developed. If you have any questions contact [email protected].