Using the detuned assay to determine HIV incidence in Ontario: Results and methodologic perspectives 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 STAHRS Workshop Centers for Disease Control Albany, New York, USA, November 14-16, 2001

MOHLTC, Laboratories Branch, IMC – 2001 Acknowledgements At the HIV LaboratoryAt the HIV Laboratory Lisa Santangelo and Cindi Farina, data collectionLisa Santangelo and Cindi Farina, data collection Lynda Healey, detuned assayLynda Healey, detuned assay Elaine McFarlane, data entry screensElaine McFarlane, data entry screens Len Neglia, mailout of questionnairesLen Neglia, mailout of questionnaires Regional PHLs, mailout of questionnairesRegional PHLs, mailout of questionnaires Physicians who prescribe HIV testing, supplementary dataPhysicians who prescribe HIV testing, supplementary data Frank McGee, AIDS Bureau for base fundingFrank McGee, AIDS Bureau for base funding Ontario HIV Treatment Network for initial project fundingOntario HIV Treatment Network for initial project funding CIDPC, Health Canada for continued project fundingCIDPC, Health Canada for continued project funding

MOHLTC, Laboratories Branch, IMC – 2001 Introduction Serodiagnostic data useful for surveillanceSerodiagnostic data useful for surveillance However,However, persons who test may not be representativepersons who test may not be representative data quality often poordata quality often poor Unbiased estimates of HIV incidence and prevalence cannot be derived directlyUnbiased estimates of HIV incidence and prevalence cannot be derived directly

MOHLTC, Laboratories Branch, IMC – 2001 Introduction Testing of HIV-positive specimens using less sensitive (“detuned”) assay permits the identification of persons who recently seroconverted;Testing of HIV-positive specimens using less sensitive (“detuned”) assay permits the identification of persons who recently seroconverted; Can calculate HIV incidence density, a critical indicator otherwise difficult to measureCan calculate HIV incidence density, a critical indicator otherwise difficult to measure

MOHLTC, Laboratories Branch, IMC – 2001 Study objectives Determine the number of persons newly testing positive for HIVDetermine the number of persons newly testing positive for HIV Determine the distribution of exposure category among newly diagnosed HIV-infected personsDetermine the distribution of exposure category among newly diagnosed HIV-infected persons Estimate HIV incidence density among persons undergoing HIV testingEstimate HIV incidence density among persons undergoing HIV testing

MOHLTC, Laboratories Branch, IMC – 2001 Data collection and management Questionnaire sent with HIV-positive resultsQuestionnaire sent with HIV-positive results and 1:200 sample of HIV-negative results Coolect data on risk factors for HIV infection and HIV test historyCoolect data on risk factors for HIV infection and HIV test history Questionnaire returned by mail, fax or telephone interviewQuestionnaire returned by mail, fax or telephone interview Data entered in Microsoft AccessData entered in Microsoft Access

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

MOHLTC, Laboratories Branch, IMC – 2001 Data analysis NumeratorNumerator Non-reactive (discordant specimens) without risk factors imputed to NIR specimens based on reclassification from LESNon-reactive (discordant specimens) without risk factors imputed to NIR specimens based on reclassification from LES Initially, imputed as proportion of those with risk factor informationInitially, imputed as proportion of those with risk factor information Denominators (testers) handled similarlyDenominators (testers) handled similarly Incidence density =Incidence density = NR * 100 Testers * (t / 365) NR * 100 Testers * (t / 365)

MOHLTC, Laboratories Branch, IMC – 2001 Study questionnaires mailed and returned, Oct Dec 2000 Questionnaires Kaplan - Meier returned by MailedReturnedProportion 4 mon. 8 mon. HIV-positiveHIV-negativeTotal1,0711,3922, ,0011,73468%72%70%72%73%79%80%

MOHLTC, Laboratories Branch, IMC – 2001 Exposure category classified according to HIV test requisition, returned questionnaires and modeled distribution, HIV-positives HIV test requisition Returned questionnaires of NIR Projected final distribution MSMMSM-IDUIDUEndemic HR hetero LR hetero OtherNIR %3%13%6%6%15%2% %2%10%21%7%21%1% %2%11%14%6%18%2% Total1, %1,071100% %NIR49%42%

MOHLTC, Laboratories Branch, IMC – 2001 Incidence (per 100 py) by exposure category Ontario, Oct Jul MSMMSM-IDUIDU HR hetero LR hetero Incidence per 100 p-y Exposure category

MOHLTC, Laboratories Branch, IMC – 2001 Incidence (per 100 py) amomg MSM, MSM-IDU and IDU by health region, Ontario, Oct 1999 – Jul Ontario TorontoOttawaOtherIDUMSMMSM-IDU

MOHLTC, Laboratories Branch, IMC – 2001 Incidence (per 100 py) among LR and HR heterosexual by health region Ontario, Oct Jul Ontario TorontoOttawaOther HR hetero LR hetero

MOHLTC, Laboratories Branch, IMC – 2001 Incidence (per 100 py) among MSM by health region and study period, Ontario, Oct Jul 2001

MOHLTC, Laboratories Branch, IMC – 2001 Incidence (per 100 py) among IDU by health region and study period, Ontario, Oct Jul 2001

MOHLTC, Laboratories Branch, IMC – 2001 HIV incidence by age group, selected exposure categories

MOHLTC, Laboratories Branch, IMC – 2001 Incidence calculated for selected exposure categories using different "window" periods with the OT assay, Jan-Jul 2001

MOHLTC, Laboratories Branch, IMC – 2001 Interpretation Number of discordant samples and HIV tests by exposure category were modeledNumber of discordant samples and HIV tests by exposure category were modeled Interpretation of HIV incidence must incorporate knowledge of patterns in HIV test seeking behavioursInterpretation of HIV incidence must incorporate knowledge of patterns in HIV test seeking behaviours Observed HIV incidence likely higher than for actual populationObserved HIV incidence likely higher than for actual population

MOHLTC, Laboratories Branch, IMC – 2001 Methodologic issues 1 Risk factors unknown for significant proportion of both HIV-positive and HIV-negative testersRisk factors unknown for significant proportion of both HIV-positive and HIV-negative testers Distribution of those with unknown risk factors different than that among those with known risk factorsDistribution of those with unknown risk factors different than that among those with known risk factors

MOHLTC, Laboratories Branch, IMC – 2001 Methodologic issues 2 Testers may include persons with risk behaviours in distant pastTesters may include persons with risk behaviours in distant past This would tend to underestimate HIV incidenceThis would tend to underestimate HIV incidence

MOHLTC, Laboratories Branch, IMC – 2001 Methodologic issues 3 For MSM, analysis with varying “window period” in later samples showed substantial decrease in estimated HIV incidence with longer interval but not for other groupsFor MSM, analysis with varying “window period” in later samples showed substantial decrease in estimated HIV incidence with longer interval but not for other groups Likely due to increased probability of HIV testing related to isolated high risk exposures and seroconversion illnessLikely due to increased probability of HIV testing related to isolated high risk exposures and seroconversion illness

MOHLTC, Laboratories Branch, IMC – 2001 Conclusions Detuned assay a powerful tool to estimate HIV incidence at low costDetuned assay a powerful tool to estimate HIV incidence at low cost However, further work is required to develop methodolgic approaches to account for missing data, unrepresentative samples and sources of bias related to HIV testing behavioursHowever, further work is required to develop methodolgic approaches to account for missing data, unrepresentative samples and sources of bias related to HIV testing behaviours