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Determining HIV Incidence in Ontario: A Laboratory Study

This study focuses on utilizing a detuned assay to accurately estimate HIV incidence density in Ontario from October 1999 to July 2000. The research aims to identify newly diagnosed HIV-positive individuals, assess exposure categories, and estimate incidence density among those undergoing HIV testing. Laboratory methods and data analysis are detailed along with summary findings, interpretations, and conclusions. The detuned assay proves valuable for HIV surveillance, elucidating epidemic trends and behavioral influences on HIV testing data. Adequate data enhancement is proposed for unbiased incidence estimation.

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Determining HIV Incidence in Ontario: A Laboratory Study

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  1. Laboratory Enhancement Study: Using the detuned assay to determine HIV incidence in Ontario October 1999 – July 2000 Robert S. Remis, Carol Major, Carol Swantee Margaret Fearon, Evelyn Wallace, Elaine Whittingham Department of Public Health Sciences, University of Toronto HIV Laboratory, Laboratory Services, Ontario Ministry of Health and Long-Term Care Public Health Branch, Ontario Ministry of Health and Long-Term Care Ontario HIV Treatment Network3rd Annual Research DayToronto, Ontario, November 9-10, 2001

  2. Acknowledgements • At the HIV Laboratory • Lisa Santangelo and Cindi Farina, data collection • Lynda Healey, detuned assay • Elaine McFarlane, data entry screens • Len Neglia, mailout of questionnaires • Regional PHLs, mailout of questionnaires • Physicians who prescribe HIV testing, supplementary data • Frank McGee, AIDS Bureau for base funding • Ontario HIV Treatment Network for initial project funding • CIDPC, Health Canada for continued project funding

  3. Introduction • Serodiagnostic data may useful for surveillance • However, • persons who test may not be representative • data quality inconsistent • True HIV incidence and HIV prevalence cannot be derived directly from data

  4. Introduction • Testing of HIV-positive specimens using less sensitive (“detuned”) assay permits the identification of persons who recently seroconverted (< 4 months) • Allows calculation of HIV incidence density, an important indicator usually difficult to measure

  5. Study objectives • To accurately determine the number of persons newly testing positive for HIV • To determine the distribution of exposure category among newly diagnosed HIV-infected persons • To estimate HIV incidence density among persons undergoing HIV testing

  6. Data collection and management • Questionnaire sent with HIV-positive results • and 1:200 sample of HIV-negative results • Data on risk factors for HIV infection and HIV test history • Questionnaire may be returned • by mail or fax • by telephone interview • Data entered in Microsoft Access

  7. Laboratory methods • Modified Abbott 3A11 EIA kit (Oct 1999-Oct 2000) • Serum diluted to 1:20,000 • Incubation period reduced to 30 minutes • Cut-off value increased • Organon-Teknika (Oct 2000-Jul 2001) • Similar principle to Abbott EIA • Allows use of variable cut-off value reflecting varying “window period”

  8. Data analysis • Numerator • Non-reactive (discordant specimens) without risk factors imputed to NIR specimens based on reclassification from LES • Initially, imputed as proportion of those with risk factor information • Denominators (testers) handled similarly • Incidence density = • NR * 100 Testers * (t / 365)

  9. Incidence (per 100 py) by exposure categoryOntario, Oct 1999 - Jul 2001

  10. Incidence (per 100 py) amomg MSM, MSM-IDU and IDU by health region,Ontario, Oct 1999 – Jul 2001

  11. Incidence (per 100 py) among LR and HR heterosexual by health regionOntario, Oct 1999 - Jul 2001

  12. Incidence (per 100 py) among MSM by health region and study period, Ontario, Oct 1999 - Jul 2001

  13. Incidence (per 100 py) among MSM-IDUby healthregion and study period, Ontario, Oct 1999 - Jul 2001

  14. Incidence (per 100 py) among IDU by health region and study period, Ontario, Oct 1999 - Jul 2001

  15. Incidence calculated for selected exposure categoriesusing different "window" periods with the OT assay, Jan-Jul 2001

  16. Summary of findings • Exposure category distribution among those with risk factor data not representative • Trends in HIV incidence • MSM Toronto: Highest but decreasing; • MSM Ottawa: Initially low but increasing; • MSM elsewhere: Intermediate and increasing • IDU: high in Ottawa; lower elsewhere

  17. Interpretation • Number of discordant samples and HIV tests by exposure category were modeled • Interpretation of HIV incidence must incorporate knowledge of patterns in HIV test seeking behaviours • Observed HIV incidence likely higher than for population

  18. Conclusions • HIV serodiagnostic program extremely useful for HIV surveillance • Detuned assay provides insights about a critical indicator of the HIV epidemic at low cost

  19. Conclusions • Due to missing and unrepresentative data on risk factors and HIV test history, available data must be enhanced through supplementary means on an ongoing basis • Estimates of HIV incidence are almost certainly biased in upward direction • Techniques to adjust or standardize will require detailed knowledge of HIV testing behaviours

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