Technical Notes: iPHIS vs. PHO data
For positive HIV tests, OHESI uses laboratory data on HIV-positive diagnostic tests from the Public Health Ontario (PHO) Laboratory along with information documented by ordering providers on test requisition forms and from the LEP.
OHESI does not use information from the integrated Public Health Information System (iPHIS). iPHIS is an electronic, web-based system used by PHUs for case-management and reporting to the Ontario Ministry of Health on diseases of public health significance, including HIV. It is the main source of data used by PHO to produce reportable disease surveillance reports. iPHIS includes information elicited during public health follow up of HIV cases.
The number of HIV diagnoses in iPHIS does not correspond to the number of positive HIV tests in PHO HIV surveillance. Potential sources of discrepancy include:
- Additional exclusion within iPHIS of repeated HIV-positive tests based on information elicited during PHU follow-up, whereas this may not be possible in PHO data due to lack of identifying information to link tests (e.g. when an HIV-positive individual initially tests anonymously and then nominally).
- Collection of risk factor and demographics differ between iPHIS and PHO data and may result in different characterization of the diagnosed population.
- iPHIS does not include HIV diagnoses that arise from testing non-Ontario residents (e.g., Quebec residents testing in Ontario are included in provincial totals in PHO HIV surveillance).
- iPHIS includes diagnoses who have moved to Ontario, been reported to the local PHU as an HIV case, but who have not received a HIV diagnostic lab test in Ontario.
- iPHIS may include more complete information on an individual’s address (obtained during public health follow up) than lab data (which is solely based on what is documented on the test requisition form), and this may influence the PHU (and hence health regions) to which an HIV case is assigned.
- Data entry errors within iPHIS that result in cases being misclassified and not captured in final counts.
- Cases may be assigned to different dates in PHO and iPHIS data (e.g., date of confirmed diagnosis vs. date of report to PHU). Therefore, case counts based on calendar year may differ.