ABSTRACT
Incidence estimation and calibration from cross-sectional data of acute infection
HIV-1 seroconvertors.
May 2007
Eustasius Musenge
Masters in Medicine in the Field of Biostatistics and Epidemiology
Supervised by: Mr E Marinda and Dr A Welte
Background: The HIV-1 incidence (a very important measure used as a proxy for
disease burden) can be estimated from a cross-sectional study. This incidence estimate
has the advantage of reducing on costs and time, thus enabling more timely
intervention; it is also ideal for developing nations. A common procedure used in
making this estimate utilizes two antibody tests (Sensitive/Less sensitive tests). Due to
the long window period of such tests (at least three months), persons classified as
recently infected would have been infected more than three months prior to the test
date. Detecting acute HIV-1 infection is very important since this is the most infectious
stage of the disease. This research report explores a method of estimating incidence
using an antibody test and a virological test, Polymerase Chain Reaction Ribonucleic
Acid (PCR-RNA).The cross-sectional data used are from the Centre for the AIDS
Programme of Research in South Africa (CAPRISA).
Methods: Actual follow-up cohort data from CAPRISA acute infection cohort (AIC),
comprised of 245 sex workers, were used to estimate the incidence of HIV-1 using a
PCR-RNA ,virology test based, incidence formula. The result obtained was compared to
the incidence estimate obtained by the classical method of estimating incidence
the AIDS
Programme of Research in South Africa (CAPRISA).
Methods: Actual follow-up cohort data from CAPRISA acute infection cohort (AIC),
comprised of 245 sex workers, were used to estimate the incidence of HIV-1 using a
PCR-RNA ,virology test based, incidence formula. The result obtained was compared to
the incidence estimate obtained by the classical method of estimating incidence
(prospective cohort follow-up). As a measure to reduce costs inherent in virological
tests (PCR-RNA), multistage pooling was discussed and several pooling strategies
simulations were proposed with their uncertainties. Point estimates and interval
estimates of the window period, window period prevalence and incidence from crosssectional
study of the AIC cohort were computed.
Findings: The mean window period was 6.6 days 95% CI: (2.7 – 13.0). The monthly
window period prevalence was 0.09423 percent 95 % CI: (0.0193 – 0.1865)%. The
incidence from the prospective cohort follow-up was 5.43 percent 95% CI: (3.9 – 9.2)
%. The incidence estimate from cross-sectional formulae was 5.21 percent 95% CI:
(4.1– 4.6). It was also shown by use of simulations that an optimum pool sample size is
obtained when at least half the samples are removed on every run.
Interpretation and recommendations: The PCR-RNA test is very sensitive at
detecting acute HIV-1 infected persons. The incidence estimate from the crosssectional
study formulae was very similar to that obtained from a follow-up study. The
number of tests needed can be reduced and a good estimate of the incidence can still be
obtained. The calibration was not accurate since the samples used were small and the
window period duration was too short, hence, it was difficult to extrapolate to the whole
population. Further work still needs to be done on the calibration of the proposed
incidence formulae as it could be a very useful public health tool.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/6745 |
| Date | 16 March 2009 |
| Creators | Musenge, Eustasius |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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