title: HIV incidence in rural South Africa: comparison of estimates from longitudinal surveillance and cross-sectional cBED assay testing.
abstract: BACKGROUND
  The BED IgG-Capture Enzyme Immunoassay (cBED assay), a test of recent HIV infection, has been used to estimate HIV incidence in cross-sectional HIV surveys. However, there has been concern that the assay overestimates HIV incidence to an unknown extent because it falsely classifies some individuals with non-recent HIV infections as recently infected. We used data from a longitudinal HIV surveillance in rural South Africa to measure the fraction of people with non-recent HIV infection who are falsely classified as recently HIV-infected by the cBED assay (the long-term false-positive ratio (FPR)) and compared cBED assay-based HIV incidence estimates to longitudinally measured HIV incidence.
  
  
  RESULTS
  We measured the long-term FPR in individuals with two positive HIV tests (in the HIV surveillance, 2003-2006) more than 306 days apart (sample size n = 1,065). We implemented four different formulae to calculate HIV incidence using cBED assay testing (n = 11,755) and obtained confidence intervals (CIs) by directly calculating the central 95(th) percentile of incidence values. We observed 4,869 individuals over 7,685 person-years for longitudinal HIV incidence estimation. The long-term FPR was 0.0169 (95% CI 0.0100-0.0266). Using this FPR, the cross-sectional cBED-based HIV incidence estimates (per 100 people per year) varied between 3.03 (95% CI 2.44-3.63) and 3.19 (95% CI 2.57-3.82), depending on the incidence formula. Using a long-term FPR of 0.0560 based on previous studies, HIV incidence estimates varied between 0.65 (95% CI 0.00-1.32) and 0.71 (95% CI 0.00-1.43). The longitudinally measured HIV incidence was 3.09 per 100 people per year (95% CI 2.69-3.52), after adjustment to the sex-age distribution of the sample used in cBED assay-based estimation.
  
  
  CONCLUSIONS
  In a rural community in South Africa with high HIV prevalence, the long-term FPR of the cBED assay is substantially lower than previous estimates. The cBED assay performs well in HIV incidence estimation if the locally measured long-term FPR is used, but significantly underestimates incidence when a FPR estimate based on previous studies in other settings is used.
authors.affiliation: Africa Centre for Health & Population Studies, University of KwaZulu-Natal, Durban, South Africa. tbarnighausen@africacentre.ac.za
authors.forename: Till
authors.initials: T
authors.lastname: Bärnighausen
authors.forename: Claudia
authors.initials: C
authors.lastname: Wallrauch
authors.forename: Alex
authors.initials: A
authors.lastname: Welte
authors.forename: Thomas A
authors.initials: TA
authors.lastname: McWalter
authors.forename: Nhlanhla
authors.initials: N
authors.lastname: Mbizana
authors.forename: Johannes
authors.initials: J
authors.lastname: Viljoen
authors.forename: Natalie
authors.initials: N
authors.lastname: Graham
authors.forename: Frank
authors.initials: F
authors.lastname: Tanser
authors.forename: Adrian
authors.initials: A
authors.lastname: Puren
authors.forename: Marie-Louise
authors.initials: ML
authors.lastname: Newell
mesh_terms: D015492:AIDS Serodiagnosis / Q000379:methods*; D000293:Adolescent; D000328:Adult; D005189:False Positive Reactions; D005260:Female; D015658:HIV Infections / Q000175:diagnosis / Q000453:epidemiology*; D015528:HIV Seroprevalence; D006801:Humans; D007124:Immunoenzyme Techniques / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance; D012424:Rural Population; D013019:South Africa / Q000453:epidemiology; D055815:Young Adult