Short Communication: Low False Recent Rate of Limiting Antigen-Avidity Assay Combined with HIV-1 RNA Data in Botswana

HIV incidence estimates are critical for monitoring HIV transmission trends and evaluating the impact of interventions. ¹ Assays for cross-sectional surveillance of HIV incidence are greatly needed because of the high costs and extended time needed to maintain prospective cohorts to directly determine incidence. Cross-sectional assays for incidence are also increasingly accepted due to improved performance of new assays and their associated algorithms. ² However, these assays can misclassify some long-term infected individuals as recent cases. ³ The frequency of such misclassifications on a population level is known as the false recent rate (FRR). The FRR can vary by geographical area, HIV-1 subtype, or presence of “elite” or viremic controllers (long-term nonprogressors), and might be affected by host genetic factors, and the extent of ARV use in the area. ^1,4 The FRR is a part of the HIV recency algorithm and it, therefore, affects the estimated HIV incidence. The existing uncertainty in estimation of HIV incidence can be partially explained by a lack of local FRR estimates. Applying multiassay algorithms that combine multiple serological assays with available clinical and epidemiological data ⁵ could reduce FRR, particularly those algorithms that utilize viral load data. ^3,6

In this study, we estimated the FRR in 1,036 HIV-infected treatment-naive individuals from longitudinal observational studies in Botswana sampled between 2004 and 2009. The HIV-positive status of enrolled individuals at baseline was determined by positive HIV antibody tests and detectable HIV-1 RNA (>400 cps/ml). Specimens were collected from ART-naive subjects enrolled in two cohorts, Dikotlana, ⁷ n = 725, and Botsogo, ⁸ n = 311, after 1.5–2 years of follow-up. The Dikotlana cohort ⁷ was from a prospective, randomized double-blind placebo-controlled longitudinal clinical trial that tested the effectiveness and safety of multivitamins and selenium supplementation in comparison with placebo in 878 HIV-infected ART-naive adults. The Botsogo cohort ⁸ was from an HIV-1 disease progression observational cohort of 442 HIV-infected, ART-naive adults who did not qualify for ART according to Botswana national guidelines at the time of enrollment. Written informed consent was obtained from all participants, and the study was approved by Harvard School of Public Health's Institutional Review Board and the Health Research Development Committee in Botswana.

Most participants were female (75.6%) and the median age was 35 (IQR 30–42) years at enrollment (Table 1). The median CD4 cell count was 394 cells/mm³ (IQR 303–524). The median HIV-1 RNA was 4.25 cps/ml (IQR 3.51–4.87). In the limiting antigen (LAg) assay, 10 specimens had optical density units below 1.5, resulting in an FRR of 0.97% (10/1,036; 95% CI 0.46–1.77). Four samples had HIV-1 RNA >1,000 cps/ml, resulting in an adjusted FRR of 0.39% (4/1,036; 95% CI 0.11–0.99).

The HIV recency algorithm that includes the LAg assay and HIV-1 RNA data produced a low FRR in the Botswana population sampled in the mid-2000s. To our knowledge, this is the first report of n LAg-avidity-based FRR for the Botswana population, and it is lower than both the 2% recommended by the WHO Incidence Assays Working Group ⁹ and previous LAg-avidity-based estimates of the FRR in other settings. ⁶ Our results support the importance of HIV-1 RNA load being included in the algorithm for estimation of HIV incidence, especially in settings with a large number of individuals on ARV like Botswana. ¹⁰