Why look at patterns in new HIV diagnoses?
HIV diagnosis is an early step in the HIV prevention, engagement and care cascade (Figure i) and is critical in order for people living with HIV to be linked to care.
Figure i. The HIV prevention, engagement, and care cascade
Ontario needs timely, accurate data on new HIV diagnoses to understand:
- the total number of people living with HIV who will need care to guide the planning and delivery of appropriate services
- trends in new diagnoses (i.e. people likely infected in the province) to help target prevention initiatives to those most at risk and evaluate their impact.
It is important to note that a new HIV diagnosis is not the same as a new HIV infection. Many people living with HIV are not diagnosed in the same year they became infected. Trends in new diagnoses can be influenced by factors other than infections, such as frequency of HIV testing and migration patterns, and it is difficult to disentangle these different effects.
What’s new with new HIV diagnoses reporting in Ontario?
This represents the first time OHESI has used data from the Laboratory Enhancement Program (LEP) as well as information collected during diagnostic testing to more accurately reflect trends in new HIV diagnoses in Ontario.
LEP data has been used to:
- update new HIV diagnoses counts and reduce double counting by removing HIV diagnoses with a documented history of a previous HIV-positive diagnosis within Ontario. For example, in the past an individual who initially tested HIV-positive through anonymous or non-nominal testing, and then later received a nominal HIV-positive test, would be counted twice. Using testing history information collected on the LEP can identify that an individual was previously known to be positive and reduce double-counting.
- identify HIV diagnoses with a documented history of a previous HIV-positive diagnosis outside Ontario (i.e. ‘out-of-province’ diagnoses). These individuals were initially diagnosed (and likely infected) outside of the province, and then moved to Ontario and were tested again. It is important to report on all new HIV diagnoses so the health system can plan services to meet the needs of all people living with HIV in Ontario. However, in some analyses, it is also important to exclude these individuals in order to understand where new HIV infections are occurring in the province and target prevention programs more effectively. (For information on the use of the LEP to remove duplicates and ‘out-of-province diagnoses’, please see the Technical Notes.)
 For this reason, historic counts and rates will differ from previous.
 Note: New HIV diagnoses includes individuals who have been previously diagnosed outside of Ontario (“out-of-province”) as well as those who are diagnosed for the first time in Ontario. See Glossary.
Where do these data come from?
- Data on new HIV diagnoses come from the Public Health Ontario Laboratory (PHOL), which conducts all HIV diagnostic testing requested by health care providers in Ontario.
- When someone gets an HIV test in Ontario, the health care provider ordering the test (e.g. a physician or HIV counselor) fills out a form that is sent to PHOL. This form, known as an HIV test requisition, collects information on the individual being tested, including their sex, age and HIV risk factors.
- If the person tests positive, the Laboratory Enhancement Program (LEP) sends a second form to the provider who ordered the test to collect information that may have been missed on the first form. Since 2009, the LEP form has collected information on race/ethnicity, country of birth, and test history (data not historically collected on the HIV test requisition).
- Data from both the requisition and LEP forms were combined to describe trends in new HIV diagnoses in Ontario.
- More information on this data can be found here.
 Race/ethnicity, country of birth, transgender identity and more options within the HIV testing history section were added to the HIV test requisition in 2018. Therefore, this information is not available currently.
What are some of the strengths of these data and our approach to presenting it?
- New HIV diagnoses are broken down by priority populations, groups of people identified as high risk of HIV transmission or experiencing a greater need for HIV related services in Ontario. Information on HIV risk factors, race/ethnicity and country of birth are used to assign an individual with a new HIV diagnosis to one (or more) priority populations. Unlike the categories traditionally used to describe new HIV diagnoses (known as exposure categories), these priority populations are not mutually exclusive. This means that an individual with a new HIV diagnosis can be assigned to more than one priority population (if applicable) – an approach which better represents Ontario’s HIV epidemic. Please see the Glossary and Technical Notes sections for more details on priority populations.
- Trends in new HIV diagnoses are presented as numbers as well as rates per 100,000 people, where possible. While numbers of diagnoses are influenced by the size of the underlying population, rates take this into account and remove population size as a possible explanation for any observed differences.
- Diagnoses are combined over two-year periods (2012/13, 2014/15 and 2016/17) to describe trends by priority population, race/ethnicity and health regions. This is done to reduce the effects of year-to-year variation (which can be particularly influential for populations with a small number of diagnoses) and more clearly present trends over time.
What are some of the limitations of these data?
- Information on race/ethnicity and priority population is missing for about a third of new HIV diagnoses so the number of HIV diagnoses attributed to a specific race/ethnicity or priority population is likely an underestimate of the actual number. If a specific priority population is more likely to be missing information on HIV risk factors or race/ethnicity, that population may be underrepresented in the data.
- Only about 50% of LEP forms provide information on previous testing history so the data may overstate the number of new diagnoses within Ontario and understate the number of out-of-province diagnoses.
- Documentation of information on the requisition/LEP forms may vary from provider to provider. For example, some providers may ask the person getting tested about their HIV risk factors and race/ethnicity, while other providers may gather this information from a previous medical chart or use clinical intuition.