FIG 3.

Heat map of readout signal intensity of all false-positive specimens identified using three commercial serological assays for the detection of SARS-CoV-2. The cutoffs used to determine cPass positivity were as follows: negative was <20% inhibition; indeterminate was 20 to <30% inhibition; and positive was ≥30% inhibition. The criteria used to determine Abbott Architect signal strength were as follows: negative was a signal-to-cutoff ratio of <1.0; weak positive was a signal-to-cutoff ratio of 1.0 to 1.2; and strong positive was a signal-to-cutoff ratio of >1.2. In this case, the cutoff refers to the sample-to-stored calibrator index (S/C) cutoff value of 1.4, and a signal-to-cutoff ratio of 1.2 corresponds to an actual readout of 1.4 × 1.2 = 1.68. The categorization for SD RDT band intensity was as follows: a score of 0 indicates no signal; 1 indicates barely visible but present; 2 indicates low intensity (i.e., faint but definitively positive); and 3 indicates medium to high intensity. PCR, polymerase chain reaction; NRCP, National Reference Centre for Parasitology.