using the detuned assay to determine hiv incidence in ontario results and methodologic perspectives l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Using the detuned assay to determine HIV incidence in Ontario: Results and methodologic perspectives PowerPoint Presentation
Download Presentation
Using the detuned assay to determine HIV incidence in Ontario: Results and methodologic perspectives

Loading in 2 Seconds...

play fullscreen
1 / 22

Using the detuned assay to determine HIV incidence in Ontario: Results and methodologic perspectives - PowerPoint PPT Presentation


  • 423 Views
  • Uploaded on

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

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Using the detuned assay to determine HIV incidence in Ontario: Results and methodologic perspectives' - Audrey


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
using the detuned assay to determine hiv incidence in ontario results and methodologic perspectives

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 WorkshopCenters for Disease Control

Albany, New York, USA, November 14-16, 2001

acknowledgements
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
introduction
Introduction
  • Serodiagnostic data useful for surveillance
  • However,
    • persons who test may not be representative
    • data quality often poor
  • Unbiased estimates of HIV incidence and prevalence cannot be derived directly
introduction4
Introduction
  • 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 measure
study objectives
Study objectives
  • Determine the number of persons newly testing positive for HIV
  • Determine the distribution of exposure category among newly diagnosed HIV-infected persons
  • Estimate HIV incidence density among persons undergoing HIV testing
data collection and management
Data collection and management
  • Questionnaire sent with HIV-positive results

and 1:200 sample of HIV-negative results

  • Coolect data on risk factors for HIV infection and HIV test history
  • Questionnaire returned by mail, fax or telephone interview
  • Data entered in Microsoft Access
laboratory methods
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”
data analysis
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)
slide10
Exposure category classified according to HIV test requisition, returned questionnaires and modeled distribution, HIV-positives
incidence per 100 py by exposure category ontario oct 1999 jul 2001

Exposure category

Incidence per 100 p-y

MSM

MSM-IDU

IDU

2.34

1.82

0.44

HR hetero

LR hetero

0.22

0.04

Incidence (per 100 py) by exposure categoryOntario, Oct 1999 - Jul 2001
incidence per 100 py amomg msm msm idu and idu by health region ontario oct 1999 jul 2001

MSM

MSM-IDU

IDU

Toronto

Ottawa

Other

3.38

0.82

1.38

6.32

18.1

0.24

0.51

1.36

0.24

Ontario

2.34

1.82

0.44

Incidence (per 100 py) amomg MSM, MSM-IDU and IDU by health region,Ontario, Oct 1999 – Jul 2001
incidence per 100 py among lr and hr heterosexual by health region ontario oct 1999 jul 2001

HR hetero

LR hetero

Toronto

Ottawa

Other

0.26

0.17

0.21

0.04

0.07

0.02

Ontario

0.22

0.04

Incidence (per 100 py) among LR and HR heterosexual by health regionOntario, Oct 1999 - Jul 2001
slide17
Incidence calculated for selected exposure categoriesusing different "window" periods with the OT assay, Jan-Jul 2001
interpretation
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 actual population
methodologic issues 1
Methodologic issues 1
  • Risk 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 factors
methodologic issues 2
Methodologic issues 2
  • Testers may include persons with risk behaviours in distant past
  • This would tend to underestimate HIV incidence
methodologic issues 3
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 groups
  • Likely due to increased probability of HIV testing related to isolated high risk exposures and seroconversion illness
conclusions
Conclusions
  • Detuned 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 behaviours