Table 1. Sample sizes used in calculating HIV incidence estimates for three clinical cohorts in the United States with two 4-assay MAAs.

		HPTN 064	HIVNET 001	HPTN 061
Length of follow-up (months)a		6 or 12b	18	12
# HIV negative		1,947	4,175	872
# HIV positivec		33	79d	246
Assays/Test results
1. BioRad-Avidity assay	# evaluated	33	79	246
	# <85%	3	24	30
2. LAg-Avidity assay	# evaluated	3	24	30
	# <2.9 OD-n	3	20	24
3. Viral load	# evaluated	3	20	24
	# >400 copies/mL	2	16	13
4. HRM diversity assay	# evaluated	2	16	13
	# <4.5 (# MAA positive)	2	16 e	9 f
4. Sequence ambiguity	# evaluated	2	16	12g
	# <0.5 (# MAA positive)	2	15 e	9 f

Abbreviations: HPTN: HIV Prevention Trials Network; HIVNET: HIV Network for Prevention Trials; MAA: multi-assay algorithm; LAg-Avidity: limited antigen avidity assay; BioRad-Avidity: avidity assay based on the BioRad 1/2+O EIA; HRM: high resolution melting.

^aCross-sectional HIV incidence estimates were obtained by testing samples collected at the end of follow-up in three clinical cohorts: HPTN 064, HIVNET 001, and HPTN 061. The number of HIV-infected vs. HIV-uninfected individuals included in the cross-sectional survey is shown.

^bParticipants in HPTN 064 were followed for either 6 or 12 months.

^cFor HPTN 064, 33 study participants had samples available for analysis; 28 were seropositive at enrollment, one had acute HIV infection at enrollment, and four acquired HIV infection during the study. For HIVNET 001, 79 of 90 HIV-infected study participants had samples available for analysis; all 79 participants were HIV-uninfected at study enrollment. For HPTN 061, 246 participants had samples available for analysis; 218 were seropositive at study enrollment, three had acute HIV infection at enrollment, and 25 acquired HIV infection during the study.

^d73 of these 79 samples were among the 808 samples from HIVNET 001 that were used to determine the window periods and shadows for the MAAs (see Figures 1 and 2).

^eOne specimen classed as MAA positive by the HRM-based MAA was classified as MAA negative by the ambiguity-based MAA.

^fOne specimen that was classified as MAA negative by the HRM-based MAA was classified as MAA positive by the ambiguity-based MAA.

^gOne specimen failed analysis with sequence ambiguity. Because the MAA could not be completed, this specimen was excluded from incidence calculations.