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Significantly diminished long-term specificity of the BED capture enzyme immunoassay among patients with HIV-1 with very low CD4 counts and those on antiretroviral therapy
Global Health Sciences Literature Digest
Published September 09, 2010
Journal Article

Marinda ET, Hargrove J, Preiser W, et al. Significantly diminished long-term specificity of the BED capture enzyme immunoassay among patients with HIV-1 with very low CD4 counts and those on antiretroviral therapy. J Acquir Immune Defic Syndr. 2010 Apr 1;53(4):496-9.

In Context

HIV incidence is a key measure for public health programs. The BED capture enzyme immunoassay (BED) is a promising laboratory assay that has been used to estimate HIV incidence using serum samples collected from cross-sectional surveys and among persons testing for HIV infection. The BED assay classifies individuals as having recent (usually within six months, on average) or long-term infection. Estimating the incidence in the population from BED test results requires assumptions and application of specific analytic tools. Studies in the United States, Africa, and Asia have found that the BED estimate can be two to three times higher than the incidence estimated using follow-up of HIV-uninfected cohorts. This is because a proportion of persons with long-term infection are classified as recently infected using the BED assay.(1, 2, 3, 4, 5)


Tygerberg Hospital HIV clinic, Western Cape, South Africa

Study Design



Frozen serum specimens from HIV-infected patients who had received antiretroviral therapy (ART) for at least one month


Proportion of long-term infections misclassified as recently acquired infections


Frozen serum samples from baseline (before starting ART) and at a single follow-up (ranged from six to 24 months) were tested using the BED assay. Testing of the first 81 samples followed routine guidelines, including retesting specimens with optical densities less than 1.2. The differences in test results upon retesting were minimal and not all additional testing included this step.


There were 1061 samples collected from 505 patients. There were 430 specimens tested with BED at baseline, 433 tested at six months, 127 tested at 12 months, 31 tested at 18 months, and nine tested at 24 months of follow-up. The mean age of patients was 33 years, and 31% were men.

The proportion of specimens that tested as recent was 11.2 % (95% confidence interval (CI): 8.3-14.5) which was independent of age and gender. Among patients with a CD4 cell count <50 cells/mm3, 20.2% tested as recent infections (95% CI: 12.4-30.1) compared with 8.8% of patients with CD4 counts of 50 cells/mm3 or above (P=0.002). Patients with CD4 counts <50 cells/mm3 and viral load levels below 4 log10 were 2.9 times more likely to falsely test recent (95% CI: 1.39-11.11) compared with patients with high CD4 and viral load levels.

The proportion of patients falsely testing as recently infected increased with follow-up time on ART. The percentage testing recent was 17% at six months, 25% at 12 months, 38% at 18 months, and 56% at 24 months. After adjusting for CD4 count, the odds of testing recent compared to baseline were 2.1 ((95% CI: 1.6-2.9), at six months, 3.5 (95% CI: 2.2-5.7) at 12 months, 6.8 (95% CI: 3.0-15.7) at 18 months, and 12.2 (95% CI: 3.2-46.1) at 24 months of follow-up.


ART and low CD4 cell counts contribute to persons being falsely classified as recently infected and point to the need to adjust for such factors in the estimation of incidence using the BED assay.

Quality Rating

This study was of very good quality. It had a large sample size, was likely to be representative of sub-Saharan African HIV-infected populations, and used a standard case definition. Important limitations to consider are that the study did not mention quality control efforts or blinding of the laboratory testing. In addition, although it is true that most persons with AIDS-related opportunistic illnesses and low CD4 cell counts have long-standing infections, this is not always the case. Estimates of the prevalence of these conditions among recently infected persons are not known, and they may substantially affect the conclusions from this study.

Programmatic Implications

The most important implication of this study is that it provides additional information regarding the limitations of the BED assay to estimate HIV incidence and, more importantly, identifies some of the factors associated with falsely testing as recently infected. Use of the BED to estimate incidence from cross-sectional surveys should ascertain the dates of prior HIV-negative and -positive tests and the use of ART and measure CD4 and viral load levels. Statistical methods used to estimate incidence with the BED should be adjusted to include these other factors. Ongoing studies will help to better determine the factors needed for use in incidence estimation with the BED.


  1. Parekh BS, Kennedy MS, Dobbs T, et al. Quantitative detection of increasing HIV type 1 antibodies after seroconversion: a simple assay for detecting recent HIV infection and estimating incidence. AIDS Res Hum Retroviruses 2002;18:295-307.
  2. Sakarovitch C, Rouet F, Murphy G, et al. Do tests devised to detect recent HIV-1 infection provide reliable estimates of incidence in Africa? J Acquir Immune Defic Syndr 2007;45:115-22.
  3. McDougal JS, Parekh BS, Peterson ML, et al. Comparison of HIV type 1 incidence observed during longitudinal follow-up with incidence estimated by cross-sectional analysis using the BED capture enzyme immunoassay. AIDS Res Hum Retroviruses 2006;22:945-52.
  4. Saphonn V, Parekh BS, Dobbs T, et al. Trends of HIV-1 seroincidence among HIV-1 sentinel surveillance groups in Cambodia, 1999-2002. J Acquir Immune Defic Syndr 2005;39:587-92.
  5. Hargrove JW, Humphrey JH, Mutasa K, et al. Improved HIV-1 incidence estimates using the BED capture enzyme immunoassay. AIDS 2008;22:511-8.